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Influence of hydrogen bonding in the paramagnetic NMR shieldings of nitronylnitroxide derivative molecules
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Biotechnology.ORCID iD: 0000-0003-2729-0290
KTH, Superseded Departments, Biotechnology.ORCID iD: 0000-0002-9123-8174
2004 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 4, 1197-1206 p.Article in journal (Refereed) Published
Abstract [en]

We apply our recently developed methodology for first-principles computations of paramagnetic NMR shieldings and explore the shieldings in a selected set of radicals that form core units in molecular magnets. The influence on these parameters of hydrogen bonding, that corresponds to the crystal environment, is the prime objective of the study. Nitronylnitroxide radicals with the hydroxyphenyl group in the ortho, meta, and para positions, as well as p-methoxyphenyl derivatives, are chosen for this purpose. The strong (NOHO)-H-... hydrogen bonding in the real crystal structure has been simulated by adding water molecules in the twelve molecular complexes investigated. Comparison of calculated and experimental data is made by taking the special features of the solid state and solution environments into account. The observed change in the shielding constant due to hydrogen bonding is explained by the spin delocalization picture; the dominating contribution is the temperature-dependent contact shielding containing the isotropic hyperfine coupling constant.

Place, publisher, year, edition, pages
2004. Vol. 108, no 4, 1197-1206 p.
Keyword [en]
NITRONYL NITROXIDE RADICALS, POLARIZED NEUTRON-DIFFRACTION, SPIN-ORBIT PSEUDOPOTENTIALS, DENSITY-FUNCTIONAL THEORY, AB-INITIO, FERROMAGNETIC INTERACTIONS, ORGANIC FERROMAGNET, MAGNETIC-PROPERTIES, AMINOXYL RADICALS, CRYSTAL PACKING
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-13641DOI: 10.1021/jp030693gISI: 000188535700008Scopus ID: 2-s2.0-0442295459OAI: oai:DiVA.org:kth-13641DiVA: diva2:326860
Note
QC 20100624Available from: 2010-06-24 Created: 2010-06-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Density Functional Theory for EPR and NMR Spin Hamiltonian Parameters
Open this publication in new window or tab >>Density Functional Theory for EPR and NMR Spin Hamiltonian Parameters
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2004. v, 51 p.
Keyword
DFT, EPR, NMR, response theory
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3760 (URN)91-7283-748-9 (ISBN)
Public defence
2004-05-27, 00:00
Note
QC 20100622Available from: 2004-05-26 Created: 2004-05-26 Last updated: 2011-09-16Bibliographically approved
2. Density functional theory for magnetic resonance parameters of radicals
Open this publication in new window or tab >>Density functional theory for magnetic resonance parameters of radicals
2003 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2003. vii, 30 p.
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-1610 (URN)91-7283-498-6 (ISBN)
Note
QC 20100629Available from: 2003-08-26 Created: 2003-08-26 Last updated: 2010-06-29Bibliographically approved
3. Density functional studies of EPR and NMR parameters of paramagnetic systems
Open this publication in new window or tab >>Density functional studies of EPR and NMR parameters of paramagnetic systems
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Experimental methods based on the magnetic resonance phenomenon belong to the most widely used experimental techniques for investigations of molecular and electronic structure. The difficulty with such experiments, usually a proper interpretation of data obtained from high-resolution spectra, opens new challenges for pure theoretical methods. One of these methods is density functional theory (DFT), that now has an advanced position among a whole variety of computational techniques. This thesis constitutes an effort in this respect, as it presents theory and discusses calculations of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) parameters of paramagnetic molecules. It is known that the experimental determination of the magnetic resonance parameters of such molecules, especially in the case of NMR, is quite complicated and requires special techniques of spectral detection. On the other hand, paramagnetics play an important role in many areas, such as molecular magnets, active centers in biological systems, and defects in inorganic conductive materials. Therefore, they have spurred great interest among experimentalists, motivating us to facilitate the interpretation of spectral data through theoretical calculations. This thesis describes new methodologies for the determination of magnetic properties of paramagnetic molecules in the framework of DFT, which have been developed in our laboratory, and their applications in calculations of a wide range of molecular systems.

The first two papers of this thesis deal with the theoretical determination of NMRparameters, such as nuclear shielding tensors and chemical shifts, in paramagnetic nitroxides that form core units in molecular magnets. The developed methodology is aimed to realize a high calculational accuracy for these systems. The effects of hydrogen bonding are also described in that context. Our theory for the evaluation of nuclear shielding tensors in paramagnetic molecules is consistent up to second order in the fine structure constant and considers orbital, fully anisotropic dipolar, and isotropic contact contributions to the shielding tensor.

The next projects concern electron paramagnetic resonance. The well-known EPR parameters, such as the g-tensors and the hyperfine coupling constants are explored. Calculations of electronic g-tensors were carried out in the framework of a spin-restricted open-shell Kohn-Sham method combined with the linear response theory recently developed in our laboratory and allowing us to avoid by definition the spin-contamination problem. The inclusion of solvent effects, described by the polarizable continuum model, extends the possibility to treat molecular systems often investigated in solution. For calculations of the hyperfine coupling constants a so-called restricted-unrestricted approach to account for the spin polarization effect has been developed in the context of DFT. To examine the validity of the approximations implicit in this scheme, the neglect ii of singlet operators, a generalized RU methodology was implemented, which includes a fully unrestricted treatment with both singlet and triplet operators. The small magnitude of the changes in hyperfine coupling constants confirms the validity of the original scheme.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 50 p.
Keyword
spin-restricted DFT, restricted-unrestricted approach, EPR spin Hamiltonian parameters, NMR spin Hamiltonian parameters
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4116 (URN)91-7178-450-0 (ISBN)
Public defence
2006-10-06, FD5, AlbaNova, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2006-09-22 Created: 2006-09-22 Last updated: 2012-03-21Bibliographically approved

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