ABINITIO CALCULATION OF THE STRUCTURES, RAMAN FREQUENCIES AND ZN NMR-SPECTRA OF TETRAHEDRAL COMPLEXES OF ZN-2+

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, ZnL Raman stretching frequencies and intensities and 67Zn NMR shielding for the tetrahedral (or S4) complexes ZnCl42-, Zn(CN)42-, Zn(OH)42- and Zn(SH)42-. The NMR shielding is found to be sensitive to the ZnX bond distance and to the confirmation (e.g. Td versus S4 for Zn(OH)42-) as well as to the identity of the ligand. We predict Zn(SH)42- to be more deshielded than any solution species yet studied (ΔσZn=-317 ppm with respect to Zn(OH2)62+) and to have a low energy (≈220 cm-1) but intense ZnS Raman active symmetric stretching vibration. © 1990.