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Hard Acid and Soft Base Stabilisation of Di‐ and Trimercury Cations in Benzene Solution – A Spectroscopic, X‐ray Scattering, and Quantum Chemical Study
Author(s) -
Ulvenlund Stefan,
Rosdahl Jan,
Fischer Andreas,
Schwerdtfeger Peter,
Kloo Lars
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199904)1999:4<633::aid-ejic633>3.0.co;2-d
Subject(s) - chemistry , benzene , raman spectroscopy , molecule , metal ions in aqueous solution , solubility , metal , density functional theory , ion , mercury (programming language) , lewis acids and bases , raman scattering , crystallography , inorganic chemistry , computational chemistry , organic chemistry , computer science , optics , programming language , catalysis , physics
Hg 2 Cl 2 dissolves in GaCl 3 /benzene solution to yield Hg 2 2+ and chlorogallate(III) ions, Ga n Cl 3 n +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 Å 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 GaCl 3 /benzene solution. In contrast, mercury is insoluble in neat liquid GaCl 3 and only sparingly soluble in GaCl 3 /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 GaCl 3 , 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 C 6 H 6 are observed in the Raman spectra: The totally symmetric C 6 H 6 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 (C 6 H 6 ) 2 2+ and Hg m Cl 2 (C 6 H 6 ) 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 (C 6 H 6 ) 2 2+ models with η 1 / quasi ‐η 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.