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  • 51. Ott, S.
    et al.
    Borgstrom, M.
    Kritikos, M.
    Lomoth, R.
    Bergquist, J.
    Akermark, B.
    Hammarstrom, L.
    Sun, Licheng C.
    Model of the iron hydrogenase active site covalently linked to a ruthenium photosensitizer: Synthesis and photophysical properties2004In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 43, no 15, p. 4683-4692Article in journal (Refereed)
    Abstract [en]

    A model of the iron hydrogenase active site with the structure [(mu-ADT)Fe-2(CO)(6)] (ADT = azadithiolate (S-CH2-NR-CH2-S), (2: R = 4-bromophenyl, 3: R = 4-iodophenyl)) has been assembled and covalently linked to a [Ru(terpy)(2)](2+) photosensitizer. This trinuclear complex 1 represents one synthetic step toward the realization of our concept of light-driven proton reduction. A rigid phenylacetylene tether has been incorporated as the linking unit in 1 in order to prolong the lifetime of the otherwise short-lived [Ru(terpy)(2)](2+) excited state. The success of this strategy is demonstrated by comparison of the photophysical properties of 1 and of two related ruthenium complexes bearing acetylenic terpyridine ligands, with those of [Ru(terpy)(2)](2+). IR and electrochemical studies reveal that the nitrogen heteroatom of the ADT bridge has a marked influence on the electronic properties of the [Fe-2(CO)(6)] core. Using the Rehm-Weller equation, the driving force for an electron transfer from the photoexcited *[Ru(terpy)(2)](2+) to the diiron site in 1 was calculated to be uphill by 0.59 eV. During the construction of the trinuclear complex 1, n-propylamine has been identified as a decarbonylation agent on the [(mu-ADT)Fe-2(CO)(6)] portion of the supermolecule. Following this procedure, the first azadithiolate-bridged dinuclear iron complex coordinated by a phosphine ligand [(mu-ADT)Fe-2(CO)(5)PPh3] (4, R = 4-bromophenyl) was synthesized.

  • 52.
    Privalov, Timofei
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Akermark, Bjorn
    Liu, Jianhui
    Gao, Yan
    Wang, Mei
    A computational study of O-O bond formation catalyzed by monoand Bis-Mn-IV-Corrole complexes2007In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 46, no 17, p. 7075-7086Article in journal (Refereed)
    Abstract [en]

    A detailed computational study of O-O bond formation, catalyzed by monomeric and dimeric Mn-corrole complexes, is reported. The model explicitly takes into account the solvent, with respect to the first and second coordination spheres, while the bulk solvent is described by the polarizable continuum model. Two reaction mechanisms are proposed and computationally characterized: the concerted and the two-step mechanisms. The concerted mechanism is based on a OH--(MnO)-O-IV interaction via the outer-sphere pathway involving the bridging solvent molecules in the first coordinating sphere. The two-step mechanism is proposed to operate via the coordination of a hydroxide to the Mn-Iv ion, forming a MnO(OH)(-)-corrole complex with a strongly nonplanar corrole ligand. Comparison of the proposed mechanisms with available experimental data. is performed.

  • 53. Purgel, Mihaly
    et al.
    Maliarik, Mikhail
    Glaser, Julius
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Platas-Iglesias, Carlos
    Persson, Ingmar
    Toth, Imre
    Binuclear Pt-TI Bonded Complex with Square Pyramidal Coordination around Pt: A Combined Multinuclear NMR, EXAFS, UV-Vis, and DFT/TDDFT Study in Dimethylsulfoxide Solution2011In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 50, no 13, p. 6163-6173Article in journal (Refereed)
    Abstract [en]

    The structure and bonding of a new Pt-Tl bonded complex formed in dimethylsulfoxide (dmso), (CN)(4)Pt-Tl(dmso)(5)(+), have been studied by multinuclear NMR and UV vis spectroscopies, and EXAFS measurements in combination with density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. This complex is formed following the equilibrium reaction Pt(CN)(4)(2-) + Tl(dmso)(6)(3+) reversible arrow (CN)(4)Pt-Tl(dmso)(5)(+) + dmso. The stability constant of the Pt-Tl bonded species, as determined using C-13 NMR spectroscopy, amounts to log K = 2.9 +/- 0.2. The (NC)(4)Pt-TI(dmso)(5)(+) species constitutes the first example of a Pt-Tl bonded cyanide complex in which the sixth coordination position around Pt (in trans with respect to the Tl atom) is not occupied. The spectral parameters confirm the formation of the metal metal bond, but differ substantially from those measured earlier in aqueous solution for complexes (CN)(5)Pt-Tl(CN)(n)(H2O)(x)(n-)(n = 0-3). The Tl-205 NMR chemical shift, delta = 75 ppm, is at extraordinary high field, while spin spin coupling constant, J(Pt-Tl) = 93 kHz, is the largest measured to date for a Pt-Tl bond in the absence of supporting bridging ligands. The absorption spectrum is dominated by two strong absorption bands in the UV region that are assigned to MMCT (Pt -> Tl) and LMCT (dmso -> Tl) bands, respectively, on the basis of MO and TDDFT calculations. The solution of the complex has a bright yellow color a's a result of a shoulder present on the low energy side of the band at 355 nm. The geometry of the (CN)(4)Pt-Tl core can be elucidated from NMR data, but the particular stoichiometry and structure involving the dmso ligands are established by using Tl and Pt L-III-edge EXAFS measurements. The Pt-Tl bond distance is 2.67(1) angstrom, the Tl-O bond distance is 2.282(6) angstrom, and the Pt-C-N entity is linear with Pt C and Pt center dot center dot center dot N distances amounting to 1.969(6) and 3.096(6) angstrom, respectively. Geometry optimizations on the (CN)(4)Pt-Tl(dmso)(5)(+) system by using DFT calculations (B3LYP model) provide bond distances in excellent agreement with the EXAFS data. The four cyanide ligands are located in a square around the Pt atom, while the Tl atom is coordinated in a distorted octahedral fashion with the metal being located 0.40 angstrom above the equatorial plane described by four oxygen atoms of dmso ligands. The four equatorial Tl-O bonds and the four cyano ligands around the Pt atom are arranged in an alternate geometry. The coordination environment around Pt may be considered as being square pyramidal, where the apical position is occupied by the Tl atom. The optimized geometry of (CN)(4)Pt-Tl(dmso)(5)(+) is asymmetrical (C-1 point group). This low symmetry might be responsible for the unusually large NMR linewidths observed due to intramolecular chemical exchange processes. The nature of the Pt-Tl bond has been studied by MO analysis. The metal metal bond formation in (CN)(4)Pt-Tl(dmso)(5)(+) can be simply interpreted as the result of a Pt(5d(z2))(2)-> Tl(6s)(0) donation. This bonding scheme may rationalize the smaller thermodynamic stability of this adduct compared to the related complexes with (CN)(5)Pt-Tl entity, wher the linear C-Pt-Tl unit constitutes a very stable bonding system.

  • 54.
    Riihimäki, Eva-Stina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Computational Comparison of Cation Coordination to Human Prion Peptide Models2006In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 45, no 21, p. 8509-8516Article in journal (Refereed)
    Abstract [en]

    The coordination of the cations Cu(II), Co(II), Rh(III), Ir(III), Ni(II), Pd(II), Pt(II), and Zn(II) to the copper-binding octapeptide region in the human prion protein has been compared through structural optimization. The initial coordination mode used in the calculations is a five-coordinated mode obtained from previously published crystallographic data for Cu(II). The computational results show that, among these cations, the coordinations of Co(II) and Rh(III) are the most similar to that of Cu(II). The cations Ni(II), Pd(II), and Pt(II) prefer a four-coordinate square-planar coordination by the peptide ligand. The paramagnetic Co(II) ion with its large quadrupole moment is not a good substitute for Cu(II) to be used in NMR spectroscopic studies of the coordinated peptide region. Rh(III) has more attractive NMR spectroscopic characteristics than Cu(II) and Co(II) and may represent a suitable substitute for Cu(II) in these types of studies. Some preliminary experimental studies using NMR spectroscopic methods indicate that Rh(III) coordinates the copper-binding octapeptide region of the human prion protein, although further studies are required to determine the mode of interaction in detail.

  • 55. Ryabov, A. D.
    et al.
    Le Lagadec, R.
    Estevez, H.
    Toscano, R. A.
    Hernandez, S.
    Alexandrova, L.
    Kurova, V. S.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Sirlin, C.
    Pfeffer, M.
    Synthesis, characterization, and electrochemistry of biorelevant photosensitive low-potential orthometalated ruthenium complexes2005In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 44, no 5, p. 1626-1634Article in journal (Refereed)
    Abstract [en]

    Redox potentials of photosensitive cyclometalated Ru derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)(2)]PF6 (2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2'-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The sigma-bound sp(2) carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(o-X-2-py)(MeCN)(4)]PF6 (1) and I-L. This trivial ligand substitution is unusual because la reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)(2)]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)(2)]PF6 (2e) has been prepared in CH2Cl2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal Ru-II/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCl), respectively. A minute irradiation 2c and 2e converts them into now species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, H-1 NMR, and UV-vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = 112) Ru-III species, presumably cis-[Ru-II(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[Ru-II(O-C6H4-2-py)(bpy)(MeCN)(MeOH)](+), and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)(ClRuORuCl)-O-III-Cl-IV(o-C6H4-2-py)(phen)]PF6, a first mu-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography.

  • 56.
    Saleemi, Mohsin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Stockholm University, Sweden.
    Tafti, Mohsen Yakhshi
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Jacquot, Alexandre
    Jaegle, Martin
    Johnson, Mats
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Chemical Synthesis of Iron Antimonide (FeSb2) and Its Thermoelectric Properties2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 4, p. 1831-1836Article in journal (Refereed)
    Abstract [en]

    Low temperature thermoelectric (TE) materials are in demand for more efficient cooling and power generation applications. Iron antimonide (FeSb2) draws great attention over the past few years because of its enhanced power factor values. Polycrystalline bulk FeSb2 nanopowder was prepared via a low-temperature molten salts approach followed by subsequent thermal treatment in synthetic air and hydrogen gas for calcination and reduction reactions, respectively. Structural analysis confirms the desired final phase with submicrometer grain size and high compaction density after consolidation using spark plasma sintering (SPS). TE transport properties revealed that the material is n-type below 150 K and p-type above this temperature; this suggests antimony vacancies in FeSb2. The electrical conductivity increased significantly, and the highest conductivity achieved was 6000 S/cm at 100 K. The maximum figure-of-merit, ZT, of 0.04 is achieved at 500 K, which is about 6 times higher than the earlier reported state-of-the art ZT value for the same material.

  • 57. Samoc, Marek
    et al.
    Dalton, Gulliver T.
    Gladysz, John A.
    Zheng, Qinglin
    Velkov, Yasen
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Norman, Patrick
    Humphrey, Mark G.
    Cubic Nonlinear Optical Properties of Platinum-Terminated Polyynediyl Chains2008In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 21, p. 9946-9957Article in journal (Refereed)
    Abstract [en]

    The wavelength dependence of the cubic nonlinearity of ligated platinum-terminated polyynes trans, trans-{(P-MeC6H4)(3)P}(2)(p-MeC6H4)Pt(C C)(n)Pt(p-C6H4Me){P(p-C6H4Me)(3)}(2) (n = 3-6, 8, 10, 12) has been examined by femtosecond Z-scan studies in the wavelength range 520-1500 nm and the results rationalized by density functional theory calculations on the model complexes trans, trans-(H3P)(2)(C6H5)Pt(C C)(n)Pt(C6H5)(PH3)(2) (n = 2-8, 10, 12). Although the final states for one- and two-photon transitions are not the same in these centrosymmetric molecules, the Z-scan studies reveal coincidences in one-photon absorption with features in the frequency dependencies of both real and imaginary parts of the cubic hyperpolarizability, as well as inflections in the frequency dependencies of the real part of gamma that correspond to resonances in the imaginary part of gamma. The theoretical studies suggest that the linear absorption spectra are dominated by (XAg)-Ag-1 -> n(1)B(3u) transitions, with the first state of B-3u symmetry playing a steadily diminishing role upon oligoyne chain lengthening. The theoretical studies also predict a red-shift of two-photon absorption (TPA) profile with increasing conjugation length, and a significant enhancement on proceeding from the shortest to the longest chromophore, trends that are observed experimentally. The experimental low-energy TPA maxima for these complexes can be approximated by a simple Gaussian profile. The sp-carbon chain-length dependence of linear and nonlinear absorption maxima enable an estimate (neglecting saturation) of 660 and 1000 nm for the infinite carbon chain, carbyne.

  • 58. Seisenbaeva, G. A.
    et al.
    Kloo, Lars A.
    KTH, Superseded Departments, Chemistry.
    Werndrup, P.
    Kessler, V. G.
    Electrochemical synthesis, X-ray single crystal, IR spectroscopic, and quantum chemical investigation of molybdenum and tungsten hexamethoxides2001In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 40, no 15, p. 3815-3818Article in journal (Refereed)
    Abstract [en]

    The anodic oxidation of molybdenum metal in MeOH at both low anodic and cathodic current density (0.025 A/cm(2)) and electrolyte temperatures kept below 20 degreesC provides sn efficient approach to Mo(OMe)(6) (I). W(OMe)(6) (II) can be obtained from the electrolytes, prepared via anodic dissolution of tungsten, by fractional crystallization. The symmetrically independent units in the structures of I and II, being isomorphous, follow the C-1 (slightly distorted D-2d) symmetry. Theoretical calculations performed for a free molecule of I indicate that this low symmetry may be the result of the packing of the molecules in the crystal, structure and also an inherent property imposed by the bonding in this compound. Crystal data for I: Mo(OMe)(6) at 22 degrees C, a = 7.0976(13), b = 6.6103(12), and c = 12.286(2) Angstrom, beta = 90.068(3)degrees, V= 576.41(18) Angstrom (3), monoclinic P2/n, Z = 2. Crystal data for II: W(OMe)(6) at 22 degreesC, a = 7.1164(19), b = 6.6414(18), and c = 12.304(3) Angstrom, beta = 90.047(5)degrees, V = 581.5(3) Angstrom (3), monoclinic P2/n, Z = 2.

  • 59. Spijksma, G. I.
    et al.
    Bouwmeester, H. J. M.
    Blank, D. H. A.
    Fischer, Andreas I.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Henry, M.
    Kessler, V. G.
    Chemistry of 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) modification of zirconium and hafnium propoxide precursors2006In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 45, no 13, p. 4938-4950Article in journal (Refereed)
    Abstract [en]

    The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr(O nPr)3(thd)]2, [Zr(OnPr)(O jPr)2(thd)]2, Zr(OjPr)(thd) 3, [Hf(OnPr)3(thd)]2, and Hf(O jPr)(thd)3 were isolated and characterized. The structure of the n-propoxide analogue of Zr(OjPr)(thd)3 could not be refined, but its existence was clearly demonstrated by XRD and 1H NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be "Zr(O jPr)2(thd)2" and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)(OjPr)(thd)2]2, which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)4 or Hf(thd)4. The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of MIV(thd) 4 has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds.

  • 60.
    Staehle, Robert
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Tong, Lianpeng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Rau, Sven
    Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2′-bipyridine-6,6′-dicarboxylate (bda) ligand: How ligand environment influences the catalytic behavior2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 3, p. 1307-1319Article in journal (Refereed)
    Abstract [en]

    A new water oxidation catalyst [RuIII(bda)(mmi)(OH 2)](CF3SO3) (2, H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid; mmi = 1,3- dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.

  • 61. Svensson, Per H.
    et al.
    Gorlov, Mikhail
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Kloo, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Dimensional Caging of Polyiodides2008In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 24, p. 11464-11466Article in journal (Refereed)
    Abstract [en]

    Two series of iodide and polyiodide chain structures have been synthesized through the employment of secondary interactions between polycation, long-chain, hydrocarbon cations. These compounds represent examples of crystal engineering, employing a simple strategy of synthesis. The two series are related, and the capacity to incorporate polyiodide ions dependent on the length of the hydrocarbon chains is indicated.

  • 62.
    Szabo, Zoltan
    et al.
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Potentiometric and multinuclear NMR study of the binary and ternary uranium(VI)-L-fluoride systems, where L is alpha-hydroxycarboxylate or glycine2000In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 39, no 22, p. 5036-5043Article in journal (Refereed)
    Abstract [en]

    Equilibria, structures, and ligand-exchange dynamics in binary and ternary U(VI)-L-F- systems, where L is glycolate, alpha -hydroxyisobutyrate, or glycine, have been investigated in 1.0 M NaClO4 by potentiometry and H-1, O-17, and F-19 NMR spectroscopy. L may be bonded in two ways: either through the carboxylate end or by the formation of a chelate. In the glycolate system, the chelate is formed by proton dissociation from the -alpha hydroxy group at around pH 3, indicating a dramatic increase, a factor of at least 10(13), of its dissociation constant on coordination to uranium(VI). The L exchange in carboxylate-coordinated UO2LF32- follows an Eigen-Wilkins mechanism, as previously found for acetate. The water exchange rate, k(aq) = 4.2 x 10(5) s(-1), is in excellent agreement with the value determined earlier for UO22+(aq). The ligand-exchange dynamics of UO2(O-CH2-COO)(2)F-3 and the activation parameters for the fluoride exchange in D2O (k(obs) = 12 s(-1), DeltaH(double dagger) = 45.8 +/- 2.2 kJ mol(-1), and DeltaS(double dagger) = -55.8 +/- 3.6 J K-1 mol(-1)) are very similar to those in the corresponding oxalate complex, with two parallel pathways, one for fluoride and one for the alpha -oxocarboxylate. The same is true for the L exchange in UO2(O-CH2-COO)(2)(2-) and UO2(oxalate)(2)(2-), The exchange of alpha -oxocarboxylate takes place by a proton-assisted chelate ring opening followed by dissociation. Because we cannot decide if there is also a parallel H+-independent pathway, only an upper limit for the rate constant, k(1) < 1,2 s(-1), can be given. This value is smaller than those in previously studied ternary systems. Equilibria and dynamics in the ternary uranium(VI)-glycine-fluoride system, investigated by F-19 NMR spectroscopy, indicate the formation of one major ternary complex, UO2LF32- and one binary complex, UO2L2 (L = H2N-CH2COO-), with chelate-bonded glycine; log beta>(*) over bar * (9) = 13.80 +/- 0.05 for the equilibrium UO22+ + H2N-CH2COO- + 3F(-) = UO2(H2N-CH2COO)F-3(2-) and log beta>(*) over bar * (11) = 13.0 +/- 0.05 for the reaction UO22+ + 2H(2)N-CH2COO- = UO2(H2N-CH2COO)(2). The glycinate exchange consists of a ring opening followed by proton-assisted steps. The rate of ring opening, 139 +/- 9 s(-1), is independent of both the concentration of H+ and the solvent, H2O or D2O.

  • 63.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    On the Mechanism of Oxygen Exchange Between Uranyl(VI) Oxygen and Water in Strongly Alkaline Solution as Studied by O-17 NMR Magnetization Transfer2010In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 11, p. 4928-4933Article in journal (Refereed)
    Abstract [en]

    The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI)) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using O-17 NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO2(OH)(4)(2-). The experimental rate equation, rate = k(ex)[TMA-OH](free)[U(VI)](2)(total) indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO2(OH)(4)(2-))(UO2(OH)(5)(3-)]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, Delta G(double dagger) = 60.8 +/- 2.4 kJ/mol is in good agreement with the value, Delta A(double dagger) approximate to Delta G(double dagger) = 52.3 +/- 5.4 kJ/mol, found by Buhl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state.

  • 64.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Grenthe, Ingmar
    Reactivity of the yl-bond in Uranyl(VI) complexes. 1. Rates and mechanisms for the exchange between the trans-dioxo oxygen atoms in (UO2)(2)(OH)(2)(2+) and mononuclear UO2(OH)(n)(2-n) complexes with solvent water2007In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 46, no 22, p. 9372-9378Article in journal (Refereed)
    Abstract [en]

    The stoichiometric mechanism, rate constant, and activation parameters for the exchange of the yl-oxygen atoms in the dioxo uranium(VI) ion with solvent water have been studied using O-17 NMR spectroscopy. The experimental rate equation, -v = k(2obs)[ UO22+](tot)(2)/[H+](2), is consistent with a mechanism where the first step is a rapid equilibrium 2U(17) O-2(2+) + 2H(2)O reversible arrow ((UO2)-O-17)(2)(OH)(2)(2+) + 2H(+), followed by the rate-determining step ((UO2)-O-17)(2)(OH)(2)(2+) + H2O reversible arrow (UO2)(2)(OH)(2) (2+) + H-2 170, where the back reaction can be neglected because the 170 enrichment in the water is much lower than in the uranyl ion. This mechanism results in the following rate equation V = d[(UO2)(2)(OH)(2)(2+) ]/dt= k(2,2)[(UO2)(2)(OH)(2)(2+)] = k2,2*beta 2.2[ UO22+](2)/[H+]2; with k(2.2) = (1.88 +/- 0.22) x 10(4) h(-1), corresponding to a half-life of 0.13 s, and the activation parameters triangle h4 = 119 +/- 13 kJ mol(-1) and triangle S* = 81 +/- 44 J mol(-1) K-1. *beta 2.2 is the equilibrium constant for the reaction 2UO(2)(2+) + 2H(2)O reversible arrow (UO2)(2)(OH)(2)(2+) + 2H(+). The experimental data show that there is no measurable exchange of the yl-oxygen in UO22+, UO2(OH)(+), and UO2(OH)(4)(2-)/ UO2(OH)(5)(3-), indicating that yl-exchange only takes place in polynuclear hydroxide complexes. There is no yl-exchange in the ternary complex (UO2)(2)(mu-OH)2(()F)(2)(oxalate)(2)(4-), indicating that it is also necessary to have coordinated water in the first coordination sphere of the binuclear complex, for exchange to take place. The very large increase in lability of the yl-bonds in (UO2)(2)(OH)(2)(2+) as compared to those of the other species is presumably a result of proton transfer from coordinated water to the yl-oxygen, followed by a rapid exchange of the resulting OH group with the water solvent. Yl-exchange through photochemical mediation is well-known for the uranyl(VI) aquo ion. We noted that 4there was no photochemical exchange in UO2(CO3)(3)(4) whereas there was a slow exchange or photo reduction in the UO2(OH)(4)(2-) / UO2(OH)(5)(3)- system that eventually led to the appearance of a black precipitate, presumably UO2.

  • 65.
    Tong, Lianpeng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Inge, A. Ken
    Stockholm University.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zou, Xiaodong
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Catalytic Water Oxidation by Mononuclear Ru Complexes with an Anionic Ancillary Ligand2013In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 5, p. 2505-2518Article in journal (Refereed)
    Abstract [en]

    Mononuclear Ru-based water oxidation catalysts containing anionic ancillary ligands have shown promising catalytic efficiency and intriguing properties. However, their insolubility in water restricts a detailed mechanism investigation. In order to overcome this disadvantage, complexes [Ru-II(bpc)(bpy)OH2](+) (1(+), bpc = 2,2'-bipyridine-6-carboxylate, bpy = 2,2'-bipyridine) and [Ru-II(bpc)(pic)(3)](+) (2(+), pic = 4-picoline) were prepared and fully characterized, which features an anionic tridentate ligand and has enough solubility for spectroscopic study in water. Using Ce-IV as an electron acceptor, both complexes are able to catalyze O-2-evolving reaction with an impressive rate constant. On the basis of the electrochemical and kinetic studies, a water nucleophilic attack pathway was proposed as the dominant catalytic cycle of the catalytic water oxidation by 1(+), within which several intermediates were detected by MS. Meanwhile, an auxiliary pathway that is related to the concentration of Ce-IV was also revealed. The effect of anionic ligand regarding catalytic water oxidation was discussed explicitly in comparison with previously reported mononuclear Ru catalysts carrying neutral tridentate ligands, for example, 2,2':6',2 ''-terpyridine (tpy). When 2(+) was oxidized to the trivalent state, one of its picoline ligands dissociated from the Ru center. The rate constant of picoline dissociation was evaluated from time-resolved UV-vis spectra.

  • 66. Tong, Lianpeng
    et al.
    Kopecky, Andrew
    Zong, Ruifa
    Gagnon, Kevin J.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Thummel, Randolph P.
    Light-Driven Proton Reduction in Aqueous Medium Catalyzed by a Family of Cobalt Complexes with Tetradentate Polypyridine-Type Ligands2015In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 16, p. 7873-7884Article in journal (Refereed)
    Abstract [en]

    A series of tetradentate 2,2':6',2":6",2"-quaterpyridine-type ligands related to ppq (ppq = 8-(1",10"phenanthrol-2"-y1)-2-(pyrid-2'-yOquinoline) have been synthesized. One ligand replaces the 1,10-phenanthroline (phen) moiety of ppq with 2,2'-bipyridine and the other two ligands have a 3,3'-polymethylene subunit bridging the quinoline and pyridine. The structural result is that both the planarity and flexibility of the ligand are modified. Co (II) complexes are prepared and characterized by ultraviolet-visible light (UVvis) and mass spectroscopy, cyclic voltammetry, and X-ray analysis. The light-driven H-2-evolving activity of these Co complexes was evaluated under homogeneous aqueous conditions using [Ru(bpy)(3)](2) as the photosensitizer, ascorbic acid as a sacrificial electron donor, and a blue light-emitting diode (LED) as the light source. At pH 4.5, all three complexes plus [Co(ppq)Cl-2] showed the fastest rate, with the dimethylene-bridged system giving the highest turnover frequency (2125 h(-1)). Cyclic voltammograms showed a significant catalytic current for H2 production in both aqueous buffer and H2O/DMF medium. Combined experimental and theoretical study suggest a formal Co(L)-hydride species as a key intermediate that triggers H-2 generation. Spin density analysis shows involvement of the tetradentate ligand in the redox sequence from the initial Co(II) state to the Co(II)-hydride intermediate. How the ligand scaffold influences the catalytic activity and stability of catalysts is discussed, in terms of the rigidity and differences in conjugation for this series of ligands.

  • 67.
    Tong, Lianpeng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Xu, Yunhua
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Cheng, Xiao
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 6, p. 3388-3398Article in journal (Refereed)
    Abstract [en]

    Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.

  • 68. Vallet, V.
    et al.
    Moll, H.
    Wahlgren, U.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Structure and bonding in solution of dioxouranium(VI) oxalate complexes: Isomers and intramolecular ligand exchange2003In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 42, no 6, p. 1982-1993Article in journal (Refereed)
    Abstract [en]

    Structural isomers of [UO2(oxalate)(3)](4-), [UO2(oxalate)F-3](3-), [UO2(oxalate)(2)F](3-), and [UO2(oxalate)(2)(H2O)](2-) have been studied by using EXAFS and quantum chemical ab initio methods. Theoretical structures and their relative energies were determined in the gas phase and in water using the CPCM model. The most stable isomers according to the quantum chemical calculations have geometries consistent with the EXAFS data, and the difference between measured and calculated bond distances is generally less than 0.05 Angstrom. The complex [UO2(oxalate)(3)](4-) contains two oxalate ligands forming five-membered chelate rings, while the third is bonded end-on to a single carboxylate oxygen. The most stable isomer of the other two complexes also contains the same type of chelate-bonded oxalate ligands. The activation energy for ring opening in [UO2(oxalate)F-3](3-), DeltaU(double dagger) = 63 kJ/mol, is in fair agreement with the experimental activation enthalpy, DeltaH(double dagger) = 45 +/- 5 kJ/mol, for different [UO2(PiCOlinate)F-3](2-) complexes, indicating similar ring-opening mechanisms. No direct experimental information is available on intramolecular exchange in [UO3(oxalate)(3)](4-). The theoretical results indicate that it takes place via the tris-chelated intermediate with an activation energy of AV = 38 kJ/mol; the other pathways involve multiple steps and have much higher activation energies. The geometries and energies of dioxouranium(VI) complexes in the gas phase and solvent models differ slightly, with differences in bond distance and energy of typically less than 0.06 Angstrom and 10 kJ/mol, respectively. However, there might be a significant difference in the distance between uranium and the leaving/entering group in the transition state, resulting in a systematic error when the gas-phase geometry is used to estimate the activation energy in solution. This systematic error is about 10 kJ/mol and tends to cancel when comparing different pathways.

  • 69. Vallet, V.
    et al.
    Wahlgren, U.
    Schimmelpfennig, B.
    Moll, H.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Solvent effects on uranium(VI) fluoride and hydroxide complexes studied by EXAFS and quantum chemistry2001In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 40, no 14, p. 3516-3525Article in journal (Refereed)
    Abstract [en]

    The structures of the complexes UO2Fn(H2O)(5-n)(2-n), n = 3-5, have been studied by EXAFS. All have pentagonal bipyramid geometry with U-F of and U-H2O distances equal to 2.26 and 2.48 Angstrom, respectively. On the other hand the complex UO2(OH)(4)(2-) has a square bipyramid geometry both in the solid state and in solution. The structures of hydroxide and fluoride complexes have also been investigated with wave function based and DFT methods in order to explore the possible reasons for the observed structural differences. These studies include models that describe the solvent by using a discrete second coordination sphere, a model with a spherical, or shape-adapted cavity in a conductor-like polarizable continuum medium (CPCM), or a combination of the two. Solvent effects were shown to give the main contribution to the observed structure variations between the uranium(VI) tetrahydroxide and the tetrafluoride complexes. Without a solvent model both UO2(OH)(4)(H2O)(2-) and UO2F4(H2O)(2-) have the same square bipyramid geometry, with the water molecule located at a distance of more than 4 Angstrom from uranium and with a charge distribution that is very near identical in the two complexes. Of the models tested, only the CPCM ones are able to describe the experimentally observed square and pentagonal bipyramid geometry in the tetrahydroxide and tetrafluoride complexes. The geometry and the relative energy of different isomers of UO2F3(H2O)(2)(-) are very similar, indicating that they are present in comparable amounts in solution. All calculated bond distances are in good agreement with the experimental observations, provided that a proper model of the solvent is used.

  • 70. Vallet, V.
    et al.
    Wahlgren, U.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    Rates and mechanism of fluoride and water exchange in UO2F53- and UO2F4(H2O) (2-) studied by NMR spectroscopy and wave function based methods2002In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 41, no 21, p. 5626-5633Article in journal (Refereed)
    Abstract [en]

    The reaction mechanism for the exchange of fluoride in UO2F53- and UO2F4(H2O)(2-) has been investigated experimentally using F-19 NMR spectroscopy at -5 degreesC, by studying the line broadening of the free fluoride, UO2F42-(aq) UO2F53-, and theoretically using quantum chemical methods to calculate the activation energy for different pathways. The new experimental data allowed us to make a more detailed study of chemical equilibria and exchange mechanisms than in previous studies. From the integrals of the different individual peaks in the new NMR spectra, we obtained the stepwise stability constant K-5 = 0.60 +/- 0.05 M-1 for UO2F53-. The theoretical results indicate that the fluoride exchange pathway of lowest activation energy, 71 kJ/mol, in UO2F53- is water assisted. The pure dissociative pathway has an activation energy of 75 kJ/mol, while the associative mechanism can be excluded as there is no stable UO2F64- intermediate. The quantum chemical calculations have been made at the SCF/MP2 levels, using a conductor-like polarizable continuum model (CPCM) to describe the solvent. The effects of different model assumptions on the activation energy have been studied. The activation energy is not strongly dependent on the cavity size or on interactions between the complex and Na+ counterions. However, the solvation of the complex and the leaving fluoride results in substantial changes in the activation energy. The mechanism for water exchange in UO2F4(H2O)(2-) has also been studied. We could eliminate the associative mechanism, the dissociative mechanism had the lowest activation energy, 39 kJ/mol, while the interchange mechanism has an activation energy that is approximately 50 kJ/mol higher.

  • 71. Vallet, Valerie
    et al.
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Structure and Bonding in Uranyl(VI) Peroxide and Crown Ether Complexes; Comparison of Quantum Chemical and Experimental Data2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 24, p. 15231-15240Article in journal (Refereed)
    Abstract [en]

    The structure, chemical bonding, and thermodynamics of alkali ions in M[12-crown-4](+), M[15-crown-5](+), and M[18-crown-6](+), M[UO2(O-2)(OH2)(2)](4,5)(+), and M[UO2(O-2)(OH)(OH2)]n(1)n (n = 4, 5) complexes have been explored by using quantum chemical (QC) calculations at the ab initio level. The chemical bonding has been studied in the gas phase in order to eliminate solvent effects. QTAIM analysis demonstrates features that are very similar in all complexes and typical for electrostatic M-O bonds, but with the M-O bonds in the uranyl peroxide systems about 20 kJ mol(-1) stronger than in the corresponding crown ether complexes. The regular decrease in bond strength with increasing M-O bond distance is consistent with predominantly electrostatic contributions. Energy decomposition of the reaction energies in the gas phase and solvent demonstrates that the predominant component of the total attractive (Delta E-elec + Delta E-orb) energy contribution is the electrostatic component. There are no steric constraints for coordination of large cations to small rings, because the M+ ions are located outside the ring plane, [O-n], formed by the oxygen donors in the ligands; coordination of ions smaller than the ligand cavity results in longer than normal MO distances or in a change in the number of bonds, both resulting in weaker complexes. The Gibbs energies, enthalpies, and entropies of reaction calculated using the conductor-like screening model, COSMO, to account for solvent effects deviate significantly from experimental values in water, while those in acetonitrile are in much better agreement. Factors that might affect the selectivity are discussed, but our conclusion is that present QC methods are not accurate enough to describe the rather small differences in selectivity, which only amount to 510 kJ mol(-1). We can, however, conclude on the basis of QC and experimental data that M[crown ether](+) complexes in the strongly coordinating water solvent are of outer-sphere type, [M(OH2)n(+)][crown ether], while those in weakly coordinating acetonitrile are of inner-sphere type, [M-crown ether](+). The observation that the M[UO2(O-2)(OH)(OH2)]n(+)n complexes are more stable in solution than those of M[crown ether](+) is an effect of the different charges of the rings.

  • 72. Wahlin, Pernilla
    et al.
    Vallet, Valerie
    Wahlgren, Ulf
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Water Exchange Mechanism in the First Excited State of Hydrated Uranyl(VI)2009In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 23, p. 11310-11313Article in journal (Refereed)
    Abstract [en]

    The water exchange mechanism of the uranyl(VI) aquo ion in the luminescent state, (3)Delta(g) in the spin-orbit free nomenclature, has been investigated using quantum chemical methods and compared to the corresponding reaction in the electronic ground state. The reaction mechanism was studied by calculation of the enthalpy of reaction of the A- and D-intermediates relative to the reactant, using a penta-aquo ion model with one additional water molecule in the second hydration sphere. The reaction barriers around the intermediates are low, and they are therefore a good approximation for the activation enthalpy. The energy of the D-intermediate is significantly larger than that of the A-intermediate both in the luminescent and in the ground states, suggesting that the water exchange is the same in both states. This suggestion is supported by the experimental rate constants for luminescence decay and water exchange in the electronic ground state that are 0.5 x 10(6) s(-1) and 1.3 x 10(6) s(-1), respectively.

  • 73. Wang, Lei
    et al.
    Mirmohades, Mohammad
    Brown, Allison
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Li, Fusheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Quentin, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Lomoth, Reiner
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Dalian Univ Technol, DUT KTH Joint Educ & Res Ctr Mol Devices, State Key Lab Fine Chem, Dalian 116024, Peoples R China.
    Hammarstrom, Leif
    Sensitizer-Catalyst Assemblies for Water Oxidation2015In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 6, p. 2742-2751Article in journal (Refereed)
    Abstract [en]

    Two molecular assemblies with one Ru(II)-polypyridine photosensitizer covalently linked to one Ru(II)(bda)L2 catalyst (1) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) and two photosensitizers covalently linked to one catalyst (2) have been prepared using a simple C-C bond as the linkage. In the presence of sodium persulfate as a sacrificial electron acceptor, both of them show high activity for catalytic water oxidation driven by visible light, with a turnover number up to 200 for 2. The linked photocatalysts show a lower initial yield for light driven oxygen evolution but a much better photostability compared to the three component system with separate sensitizer, catalyst and acceptor, leading to a much greater turnover number. Photocatalytic experiments and time-resolved spectroscopy were carried out to probe the mechanism of this catalysis. The linked catalyst in its Ru(II) state rapidly quenches the sensitizer, predominantly by energy transfer. However, a higher stability under photocatalytic condition is shown for the linked sensitizer compared to the three component system, which is attributed to kinetic stabilization by rapid photosensitizer regeneration. Strategies for employment of the sensitizer-catalyst molecules in more efficient photocatalytic systems are discussed.

  • 74. Wang, Ning
    et al.
    Wang, Mei
    Liu, Jihong
    Jin, Kun
    Chen, Lin
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Preparation, Facile Deprotonation, and Rapid H/D Exchange of the mu-Hydride Diiron Model Complexes of the FeFe -Hydrogenase Containing a Pendant Amine in a Chelating Diphosphine Ligand2009In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 24, p. 11551-11558Article in journal (Refereed)
    Abstract [en]

    The CO-displacement of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-Ph2PCH2N(n-Pr)CH2PPh2}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(μ-pdt){μ-Ph2PCH2N(n-Pr)CH2PPh2}{Fe(CO)2}2] (2) and the intermolecular bridging complex [{μ,κ11-Ph2PCH2N(n-Pr)CH2PPh2}{(μ-pdt)Fe2(CO)5}2] (3). In contrast, the reaction of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2NR (R = n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me3NO·2H2O in CH3CN at room temperature. The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(HNHμ)](OTf)2] were determined by X-ray analyses. The protonation processes of 1 with HBF4·Et2O and HOTf were studied in different solvents. The presence of the Hμ···HN interaction in [1(HNHμ)]2+ was studied by relaxation time T1 and spin saturation transfer measurements. The μ-hydride of [1(Hμ)]+ and [1(HNHμ)]2+ undergo facile deprotonation with aniline and rapid H/D exchange with deuterons in solution. In contrast, neither deprotonation nor H/D exchange was detected for [(μ-H)(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-dppp)}]+ ([5(Hμ)]+, dppp = Ph2PCH2CH2CH2PPh2) without internal base.

  • 75. Wang, Ning
    et al.
    Wang, Mei
    Liu, Tianbiao
    Li, Ping
    Zhang, Tingting
    Darensbourg, Marcetta Y.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    CO-migration in the ligand substitution process of the chelating diphosphite diiron complex (mu-pdt) Fe(CO)(3) Fe(CO){(EtO)(2)PN(Me)P(OEt}(2)2008In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 47, no 15, p. 6948-6955Article in journal (Refereed)
    Abstract [en]

    Selective synthetic routes to isomeric diiron dithiolate complexes containing the (EtO)(2)PN(Me)P(OEt)(2) (PNP) ligand in an unsymmetrical chelating role, for example, (mu-pdt)[Fe(CO)(3)][Fe(CO)(kappa(2)-PNP)] (3) and as a symmetrically bridging ligand in (mu-pdt)(mu-PNP)[Fe(CO)(2)](2) (4), have been developed. 3 was converted to 4 in 75% yield after extensive reflux in toluene. The reactions of 3 with PMe3 and P(OEt)(3) afforded bis-monodentate P-donor complexes (mu-pdt)[Fe(CO)(2)PR3][Fe(CO)(2)(PNP)] (PR3 = PMe3 5; P(OEt)(3), 7), respectively, which are formed via an associative PMe3 coordination reaction followed by an intramolecular CO-migration process from the Fe(CO)3 to the Fe(CO)(PNP) unit with concomitant opening of the Fe-PNP chelate ring. The PNP-monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex (mu-pdt)(mu-PNP)[Fe(CO)PR3][Fe(CO)(2)] (PR3 = PMe3, 6; P(OEt)(3), 8) on release of 1 equiv CO when refluxing in toluene. Variable-temperature P-31 NMR spectra show that trisubstituted diiron complexes each exist as two configuration isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.

  • 76. Wang, Xiaolin
    et al.
    Yang, Huiqing
    Wen, Yaping
    Wang, Li
    Li, Junfeng
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, Jinglai
    Comprehension of the Effect of a Hydroxyl Group in Ancillary Ligand on Phosphorescent Property for Heteroleptic Ir(III) Complexes: A Computational Study Using Quantitative Prediction2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 15, p. 8986-8995Article in journal (Refereed)
    Abstract [en]

    A new Ir(III) complex (dfpypya)(2)Ir(pic-OH) (2) is theoretically designed by introduction of a simple hydroxyl group into the ancillary ligand on the basis of (dfpypya)(2)Ir(pic) (1) with the aim to get the high efficiency and stable blue-emitting phosphors, where dfpypya is 3-methyl-6-(2',4'-difluoro-pyridinato)pyridazine, pic is picolinate, and pic OH is 3-hydroxypicolinic acid. The other configuration (dfpypya)(2)Ir(pic OH)' (3) is also investigated to compare with 2. The difference between 2 and 3 is whether the intramolecular hydrogen bond is formed in the (dfpypya)(2)Ir(pic OH). The quantum yield is determined by three different methods including the semiquantitative and quantitative methods. To quantitatively determine the quantum yield is still not an easy task to be completed. This work would provide some useful advices to select the suitable method to reliably evaluate the quantum yield. Complex 2 has larger quantum yield and more stability as compared with 1 and 3. The formation of intramolecular hydrogen bond would become a new method to design new phosphor with the desired properties.

  • 77. Wolpher, Henriette
    et al.
    Sinha, Subrata
    Pan, Jingxi
    Johansson, Anh
    Lundqvist, Maria J.
    Persson, Petter
    Lomoth, Reiner
    Bergquist, Jonas
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sundstrom, Villy
    Akermark, Bjorn
    Polivka, Tomas
    Synthesis and electron transfer studies of ruthenium-terpyridine-based dyads attached to nanostructured TiO22007In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 46, no 3, p. 638-651Article in journal (Refereed)
    Abstract [en]

    A series of bis(terpyridine)Ru-II complexes have been prepared, where one of the terpyridines is functionalized in the 4'-position by a phosphonic or carboxylic acid group for attachment to TiO2. The other is functionalized, also in the 4'-position, by a potential electron donor. In complexes 1a, 3a, and 4a,b, this donor is tyrosine or hydrogen-bonded tyrosine, while in 2a it is carotenoic amide. The synthesis and photophysical properties of the complexes are discussed. On irradiation with visible light, the formation of a long-lived charge-separated state was anticipated, via primary electron ejection into the TiO2, followed by secondary electron transfer from the donor to the photogenerated Ru-III. However, such a charge-separated state could be observed with certainty only with complex 2a. To explain the result, quantum chemical calculations were performed on the different types of complexes.

  • 78.
    Xu, Yunhua
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Åkermark, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Gyollai, Viktor
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zou, Da-Peng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Eriksson, Lars
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Zhang, Rong
    Åkermark, Björn
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    A New Dinuclear Ruthenium Complex as an Efficient Water Oxidation Catalyst2009In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 7, p. 2717-2719Article in journal (Refereed)
    Abstract [en]

    A dinuclear ruthenium complex, which acts as a molecular catalyst for water oxidation, has been synthesized and characterized. The electronic and electrochemical properties were studied by UV-vis spectroscopy and cyclic voltammetry. The oxidation potentials of the complex are significantly lowered by introducing a negatively charged carboxylate ligand, in comparison with those of the reported complexes that have neutral ligands. The catalytic activity of the complex toward water oxidation using Ce(NH4)(2)(NO3)(6) as a chemical oxidant was investigated by means of an oxygen electrode and mass spectrometry. The turnover number of this catalyst with Ce-IV as the chemical oxidant was found to be ca. 1700. The mass spectroscopic analysis of the isotopomer distribution in oxygen evolved from O-18-labeled water indicates that O atoms in the evolved oxygen originate from water.

  • 79.
    Xue, Liqin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A DFT Study: Why Do [Ni((P2N2R')-N-R)(2)](2+) Complexes Facilitate the Electrocatalytic Oxidation of Formate?2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 7, p. 3281-3289Article in journal (Refereed)
    Abstract [en]

    We present a DFT study of the reaction mechanism on electrocatalytic oxidation of formate by a family of [Ni((P2N2R')-N-R)(2)](2+) complexes ((P2N2R')-N-R = 1,5-diR'-3,7-diR derivative of 1,5-diaza-3,7-diphosphacyclooctane, where R and R' are aryl or alkyl groups). [Ni((P2N2Me)-N-Ph)(2)](2+) complex 1 was used as a model complex to mimic a family of [Ni((P2N2R')-N-R)(2)](2+) complexes. Our calculated results show that the decarboxylation step (corresponding to TS3) is the rate-determining step for the electrocatalytic oxidation of formate and that a NiII-H intermediate is involved in the reaction mechanism. The pendant amine plays an important role in the deprotonation of the nickel hydride complex generated in the decarboxylation step. In addition, our study indicates that the choice of external bases is important for removing the proton (H+) from the nitrogen-protonated nickel(0) complexes. For the electrocatalytic oxidation of formate using the catalytically inactive [Ni(depe)(2)](2+) (depe = 1,2-bis(diethylphosphino)ethane) complex, calculations on 1-depe have also been carried out for comparison.

  • 80. Zhang, Pan
    et al.
    Jacques, Pierre-Andre
    Chavarot-Keridou, Murielle
    Wang, Mei
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fontecave, Marc
    Artero, Vincent
    Phosphine Coordination to a Cobalt Diimine-Dioxime Catalyst Increases Stability during Light-Driven H-2 Production2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 4, p. 2115-2120Article in journal (Refereed)
    Abstract [en]

    The combination of cobalt diimine-dioxime complexes with a cyclometalated iridium photosensitizer gives efficient systems for hydrogen generation under visible-light irradiation using triethylamine as a sacrificial electron donor. Interestingly, the addition of triphenylphosphine (PPh3) to the medium results in a significant improvement of the stability of the system, with up to similar to 700 turnovers achieved within 10 h. UV-visible spectroscopic monitoring of the reaction allows identification of a PPh3-coordinated Co-I intermediate as the active species. Mechanistic issues regarding (i) the photogeneration of the Co-I species, (ii) the nature of the active species, and (iii) the influence of PPh3 on the H-2-evolution mechanism are discussed.

  • 81. Zhang, W.
    et al.
    Zhang, F.
    Wang, Yong-Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Song, B.
    Zhang, R.
    Yuan, J.
    Red-Emitting Ruthenium(II) and Iridium(III) Complexes as Phosphorescent Probes for Methylglyoxal in Vitro and in Vivo2017In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 3, p. 1309-1318Article in journal (Refereed)
    Abstract [en]

    Transition-metal complexes, ruthenium(II) and iridium(III) complexes in particular, with fascinating triplet emissions are rapidly emerging as important phosphorescent dyes for application in the sensing and imaging of biological makers in live cells and organisms. In this contribution, two red-emitting transition-metal complexes, [Ru(bpy)2(DA-phen)](PF6)2 and [Ir(ppy)2(DA-phen)](PF6) (bpy = 2,2′-bipyridine, DA-phen = 4,5-diamino-1,10-phenanthroline, and ppy = 2-phenylpyridine), were designed and synthesized as phosphorescent probes for the highly sensitive and selective detection of methylglyoxal (MGO), an essential biomarker in the etiopathogenesis of several diseases. Both probes showed weak emissions in aqueous media because of the existence of an effective photoinduced-electron-transfer process, while their emissions could be remarkably enhanced upon the addition of MGO. The photophysical and electrochemical properties, as well as phosphorescent responses of the probes toward MGO, were examined. The ground- and excited-state properties of the probes and their reaction products with MGO, [Ru(bpy)2(MP-phen)](PF6)2 and [Ir(ppy)2(MP-phen)](PF6) (MP-phen = 2-methylpyrazino-1,10-phenanthroline), the sensing mechanism, and several important experimental facts were investigated and validated using density functional theory (DFT)/time-dependent DFT computations. The results indicated that the phosphorescence switch-ON is due to the elimination of electron transfer and followed the reestablishment of emissive triplet excited states. To evaluate the feasibility of [Ru(bpy)2(DA-phen)](PF6)2 and [Ir(ppy)2(DA-phen)](PF6) as bioprobes, their cytotoxicity was examined, and their applicability for visualizing intracellular and in vivo MGO was demonstrated.

  • 82. Zheng, D.
    et al.
    Wang, M.
    Chen, L.
    Wang, N.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Redox reactions of [FeFe]-hydrogenase models containing an internal amine and a pendant phosphine2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 3, p. 1555-1561Article in journal (Refereed)
    Abstract [en]

    A diiron dithiolate complex with a pendant phosphine coordinated to one of the iron centers, [(μ-SCH2)2N(CH2C 6H4-o-PPh2){Fe2(CO)5}] (1), was prepared and structurally characterized. The pendant phosphine is dissociated together with a CO ligand in the presence of excess PMe3, to afford [(μ-SCH2)2N(CH2C 6H4-o-PPh2){Fe(CO)2(PMe 3)}2] (2). Redox reactions of 2 and related complexes were studied in detail by in situ IR spectroscopy. A series of new Fe IIFeI ([3]+ and [6]+), Fe IIFeII ([4]2+), and FeIFe I (5) complexes relevant to Hox, Hox CO, and Hred states of the [FeFe]-hydrogenase active site were detected. Among these complexes, the molecular structures of the diferrous complex [4]2+ with the internal amine and the pendant phosphine co-coordinated to the same iron center and the triphosphine diiron complex 5 were determined by X-ray crystallography. To make a comparison, the redox reactions of an analogous complex, [(μ-SCH2)2N(CH 2C6H5){Fe(CO)2(PMe 3)}2] (7), were also investigated by in situ IR spectroscopy in the absence or presence of extrinsic PPh3, which has no influence on the oxidation reaction of 7. The pendant phosphine in the second coordination sphere makes the redox reaction of 2 different from that of its analogue 7.

  • 83. Zheng, Dehua
    et al.
    Wang, Mei
    Wang, Ning
    Cheng, Minglun
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Dalian University of Technology (DUT), China.
    Effect of Bridgehead Steric Bulk on the Intramolecular C-H Heterolysis of [FeFe]-Hydrogenase Active Site Models Containing a P2N2 Pendant Amine Ligand2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 2, p. 411-418Article in journal (Refereed)
    Abstract [en]

    A series of pendant amine-containing [FeFe]-hydrogenase models, [X(CH2S-μ)2{Fe(CO)3}{Fe(CO)(P2 PhN2 Bn)}] (1H, X = CH2; 2Me, C(CH3)2; 3Et, C(CH2CH3)2; and P2 PhN2 Bn = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) with different groups at the bridgehead carbon of the S-to-S linker were synthesized. The oxidations of these complexes as well as the reverse reduction reaction were studied by cyclic voltammetry and in situ IR spectroscopy. Regardless of the bridgehead steric bulk, all three complexes demonstrate intramolecular iron-mediated C(sp3)-H bond heterolytic cleavage with the assistance of the pendant amine base within the chelating diphosphine ligand in the two-electron oxidation process. X-ray crystallographic analysis shows that the doubly oxidized products, [1′H]+, [2′Me]+, and [3′Et]+, all have a rigid FeSC three-membered ring at the open apical site of the rotated iron center. The most noticeable difference in structures of the oxidized complexes is that the single CO ligand of the rotated Fe(P2 PhN2 Bn)(CO) unit in [1′H]+ and [2′Me]+ is found below the Fe⋯Fe vector, while in [3′Et]+ an unusually rotated Fe(P2 PhN2 Bn)(CO) moiety positions one of the P donors within the bidentate ligand under the Fe⋯Fe vector. The starting FeIFeI complexes can be recovered from their corresponding doubly oxidized complexes by reduction in the presence of Brönsted acid.

12 51 - 83 of 83
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