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

Abstract

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.