Designing metal hydride complexes for water splitting reactions: a molecular electrostatic potential approach

Abstract

The hydridic character of octahedral metal hydride complexes of groups VI, VII and VIII has been systematically studied using molecular electrostatic potential (MESP) topography. The absolute minimum of MESP at the hydride ligand (V_min) and the MESP value at the hydride nucleus (V_H) are found to be very good measures of the hydridic character of the hydride ligand. The increasing/decreasing electron donating feature of the ligand environment is clearly reflected in the increasing/decreasing negative character of V_min and V_H. The formation of an outer sphere metal hydride–water complex showing the H⋯H dihydrogen interaction is supported by the location and the value of V_min near the hydride ligand. A higher negative MESP suggested lower activation energy for H₂ elimination. Thus, MESP features provided a way to fine-tune the ligand environment of a metal-hydride complex to achieve high hydridicity for the hydride ligand. The applicability of an MESP based hydridic descriptor in designing water splitting reactions is tested for group VI metal hydride model complexes of tungsten.