Geometrical and Linkage Isomers of [OsCl2(dmso)4] − The Complete Picture

• Published in: European journal of inorganic chemistry Vol. 2003; no. 17; pp. 3160 - 3166
• Main Authors: Alessio, Enzo, Serli, Barbara, Zangrando, Ennio, Calligaris, Mario, Panina, Natalia S.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-09-2003; WILEY‐VCH Verlag
• Subjects: Density functional calculations; Dimethyl sulfoxide; Isomerizations; Osmium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200300132

The isomerisation between the three known isomers of the [OsCl2(dmso)4] complex — trans‐[OsCl2(dmso‐S)4] (1), cis,fac‐[OsCl2(dmso‐S)3(dmso‐O)] (2), and cis‐[OsCl2(dmso‐S)4] (3) — has been investigated by NMR spectroscopy, X‐ray crystallographic analysis, and DFT calculations. We show that the two dmso‐linkage isomers 2 and 3 equilibrate slowly at room temperature in solutions of both dimethyl sulfoxide (DMSO) and light‐protected chloroform. Although crystals of 2 precipitate from DMSO solutions, crystals of 3 were obtained from chloroform solutions. Compound 2 isomerises to 1 after exposure to sunlight, while 1 transforms into 2 in hot DMSO solution. The molecular energies were calculated by DFT methods, which show that in the gas phase there are small differences in the total energies (Et), with 1 exhibiting the lowest energy, in contrast with its low population in solution. This result indicates that the stability of each isomer in solution is not simply determined by Et, but that the solvent plays an important role. In fact, quantum chemical calculations for the isomerisation process 1 ⇄ 2 show a marked increase in the equilibrium constant with increasing the solvent polarity. The calculation of the metal−dmso binding energies, in combination with the X‐ray data, shows a significantly higher strength of Os−S bonds with respect to Ru−S bonds, which explains the different behaviour of otherwise analogous osmium−dmso and ruthenium−dmso complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)