Ab initio calculation of the structures, Raman frequencies and Zn NMR spectra of tetrahedral complexes of Zn 2+

Abstract

Zn is an important trace element in the natural aqueous environment whose speciation can be studied by Raman and/or 67Zn NMR spectroscopy. We present ab initio Hartree—Fock calculations using polarized split-valence bases of the equilibrium structures, ZnL Raman stretching frequencies and intensities and 67Zn NMR shielding for the tetrahedral (or S 4) complexes ZnCl 4 2−, Zn(CN) 4 2−, Zn(OH) 4 2− and Zn(SH) 4 2−. The NMR shielding is found to be sensitive to the ZnX bond distance and to the confirmation (e.g. T d versus S 4 for Zn(OH) 4 2−) as well as to the identity of the ligand. We predict Zn(SH) 4 2− to be more deshielded than any solution species yet studied (Δσ Zn=−317 ppm with respect to Zn(OH 2) 6 2+) and to have a low energy (≈220 cm −1) but intense ZnS Raman active symmetric stretching vibration.