On the structure, infrared and Raman spectra of the 2:1 cysteine–Zn complex

Abstract

A recent study on the Raman spectrum of the cysteine zwitterion and anion, and the 2:1 (Cys)₂Zn complex was reanalyzed employing B3LYP/6-311++G(3df,2pd) calculations in a simulated water environment. The spectra were rediscussed in light of the apparent incorrect structure determined in the original paper for this complex. The complex turns out to be tetrahedral and tetracoordinated instead of octahedral hexacoordinated, as initially proposed. The calculated Raman spectrum of the complex agrees very well with the experimental data, showing that both the geometrical and electronic structures are well represented. Three metal–ligand bands are found, two of them involving mostly the symmetrical and asymmetrical stretching of the Zn–N and Zn–S bonds. They were measured at 334 and 296 cm⁻¹ and calculated at 319 and 249 cm⁻¹, respectively. The third band involves the stretching of Zn–S bonds but also skeletal vibrations of the ligand. This band, measured at 399 cm⁻¹ and calculated at 444 cm⁻¹, has been previously assigned incorrectly to a Zn–O bond which does not actually exists since the CO ⁻¹₂ fragments are located away from the Zn ion.