Cadmium-113 Fourier Transform Nuclear Magnetic Resonance and Raman Spectroscopic Studies of Cadmium(II)-Sulfur Complexes, Including [Cd₁₀(SCH₂CH₂OH)₁₆]⁴⁺

The ¹¹³Cd Fourier transform NMR and Raman spectra (1700-100 cm^-1) of a series of Cd(II) chelate complexes (derived from dithiocarbamate, xanthate, dithiophosphinate, and dithiolate ligands), Cd(SCH₂CH₂OH)₂, and [Cd₁₀- (SCH₂CH₂OH)₁₆]⁴⁺ have been determined. Cd-S stretching vibrations have been assigned to bands in the 220-144-cm^-1 interval. ¹¹³Cd chemical shifts of chelate complexes exhibited no trend in terms of the extent of sulfur ligation, but the nuclear deshielding sequence Cd(SR)2 < Cd(SR)3 < Cd(SR)₄ is indicated by measurements on the 1:2 cadmium-(II)-glutathione complex and the decanuclear cation, which contains sites of the latter two types. The solution stability of [Cd₁₀(SCH₂CH₂OH)₁₆]⁴⁺ has been investigated by ¹H and ¹¹³Cd NMR and Raman spectroscopy from -40 to +100°C. It is concluded that small structural differences may exist between the crystalline and solution phases, arising mainly from partial rupture of [formula omitted] chelate rings known to be present in the crystal, and that the solution structure approaches that in the crystal as solution temperatures are lowered below ca. 20-25 °C. From data obtained in this and previous studies a provisional ¹¹³Cd chemical shift scale is presented in terms of the types of ligand atoms in the primary coordination sphere of Cd(II). A conspicuous feature of this scale is the marked deshielding effect of thiolate sulfur vs. oxygen, halide, and nitrogen ligands relative to the reference zero of chemical shift, 0.1 M aqueous Cd(ClO₄)₂ at 25 °C. Possible application of the deshielding sequence to investigation of cadmium-cysteinate binding in metallothionein proteins is suggested.