Ab initio molecular-orbital study of the binding of ZnII with SH2 and SH−

This paper reports an ab initio molecular-orbital (MO ) study of binding of SH₂ and SH^? with Zn^II. The mechanism of binding of Zn^II with these ligands is investigated using a detailed analysis of the energy decomposition and of the electronic distribution. The dependence of the results on the choice of the basis set for sulfur (in particular the effect of incorporation of diffuses p and d orbitals) on the geometry of ligand binding, the binding energy, and the proton affinity of SH^? are investigated. Comparison made with the corresponding results concerning the binding of OH₂, OH^?, and NH₃ shows that sulfur binding is less favorable although more covalent. Both sulfur ligands show a marked preference for angular conformations for binding with the metal ion. The effect of Zn^II binding on the ease of deprotonation of H₂S is quite similar to the corresponding effect found earlier for H₂O.