Study of an S = 1 Ni(II) 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 H2 production at low overpotentials, is studied by using temperature-dependent paramagnetic (1)H NMR. The NMR T1 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.