Study of an S=1 NiII pincer electrocatalyst precursor for aqueous hydrogen production based on paramagnetic 1H NMR

A tridentate NNN Ni-II complex, shown to be an electrocatalyst for aqueous H-2 production at low over-potentials, is studied by using temperature-dependent paramagnetic H-1 NMR. The NMR T-1 relaxation rates, temperature dependence of the chemical shifts, and dc SQUID magnetic susceptibility are correlated to DFT chemical shifts and compared with the properties of a diamagnetic Zn analogue complex. The resulting characterization provides an unambiguous assignment of the six proton environments in the meridionally coordinating tridentate NNN ligand. The demonstrated NMR/DFT methodology should be valuable in the search for appropriate ligands to optimize the reactivity of 3d metal complexes bound to attract increasing attention in catalytic applications.