Hard Acid and Soft Base Stabilisation of Di- and Trimercury Cations in Benzene Solution - A Spectroscopic, X-ray Scattering, and Quantum Chemical Study
1999 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-0682, no 4, 633-642 p.Article in journal (Refereed) Published
Hg2Cl2 dissolves in GaCl3/benzene solution to yield Hg-2(2+) and chlorogallate(III) ions, GanCl3n+1-. In such solutions, Hg-2(2+) can be reduced to Hg-3(2+) by metallic mercury. Solubility measurements show that one mol of Hg is oxidised per mol of Hg-2(2+). The Hg-3(2+) ion gives a strong band at 110 cm(-1) in the Raman spectrum and Hg-Hg correlations at about 2.60 and 5.15 Angstrom in the radial distribution function obtained by Liquid X-ray scattering. - Hg-3(2+) can also be synthesised in high yield by direct oxidation of metallic mercury by Ga-III in GaCl3/benzene solution. In contrast, mercury is insoluble in neat Liquid GaCl3 and only sparingly soluble in GaCl3/KCl melts. It therefore seems likely that the thermodynamic stabilisation of subvalent mercury species in benzene solution not only relies on the traditional acid stabilisation provided by the hard Lewis acid GaCl3, but also on a "soft-base stabilisation" provided by interactions between the aromatic molecules and the cations. Evidence for such specific interactions between Hg-m(2+) cations and C6H6 are observed in the Raman spectra: The totally symmetric C6H6 band at 991 cm(-1) is found to split in the presence of Hg-m(2+) ions and to give new peaks at 978 (m = 2) and 982 (m = 3) cm(-1). - In order to further elucidate the cluster-arene interactions, ab initio and density functional calculations were performed for the model compounds Hg-m(C6H6)(2)(2+) and HgmCl2(C6H6)(2), m = 2 and 3. The calculations show that both models represent coordinations modes which are feasible for Hg-m(2+) ions. However, the calculated vibrational frequencies for the Hg-m(C6H6)(2)(2+) models with eta(1)/quasi-eta(3) coordination of the benzene molecules along the Hg-Hg vector are most consistent with the body of experimental and literature data. The counterions are thus suggested to occupy secondary coordination sites.
Place, publisher, year, edition, pages
1999. no 4, 633-642 p.
mercury cations, subvalent compounds, ab initio calculations, liquid X-ray scattering
IdentifiersURN: urn:nbn:se:kth:diva-5104ISI: 000079454900009OAI: oai:DiVA.org:kth-5104DiVA: diva2:7869
QC 201010112005-05-152005-05-152010-10-11Bibliographically approved