Comparison of the coordination geometries of Zn(II) and Cd(II) ions in complexes with water, methanol and bulky aryloxysilanethiolate ligands

Zinc and cadmium complexes containing silanethiolate anions and methanol or water were synthesized and characterized by X-ray diffraction, FT-IR and NMR spectroscopy, and DFT calculations. The Zn/Cd complexes 1 and 2 exhibit the same composition but different coordination spheres of the metal ions, [Cd{SSi(OAr)3}2(CH3OH)]·CH3OH (1) versus [Zn{SSi(OAr)3}2(CH3OH)2] (2) where Ar = 2,6-diisopropylphenyl. Contrary to zinc, the cadmium ion utilizes very weak donors to complete its coordination sphere; it forms contacts to phenyl rings of the silanethiolate ligand. Two zinc analogs of the general formula [Zn{SSi(OAr)3}2(L)2] where L = CH3OH (2) or H2O (3) are compared. In 3, methanol is replaced by water even at low concentration of water in the reaction mixture. The exchange is accompanied by the reorganization of the hydrophobic environment of the water/methanol ligand in the complex. A tetranuclear zinc complex [Zn4(CH3OH)4{SSi(OAr)3}4(CH3COO)4] 4 featuring an unusual unsupported [Zn4(CH3COO)4]4+ core was also obtained and characterized.

Zinc and cadmium silanethiolates with methanol/water co-ligands were prepared and characterized by means of infrared spectroscopy, 1H, 13C and 113Cd NMR spectroscopy, and single-crystal X-ray diffraction. Facile exchange of methanol to water within zinc complex was observed similar to the process undergoing in the active site of alcohol dehydrogenase.Figure optionsDownload as PowerPoint slide