Synthesis, crystal structure and electrocatalytic hydrogen evolution reaction studies of cobaloximes with diphenylglyoxime and carboxylic acid functionalized neutral bases

Abstract

Eight halocobaloximes of general formula {XCo(dpgH)2B}, containing dipheylglyoxime (dpgH) have been synthesized and characterized with two different halide ligands (X = Cl-, Br-) and four types of carboxylic acid functionalized neutral bases (B = pyridine 3,5-dicarboxylic acid, p-aminobenzoic acid, indole-2-carboxylic acid and isonicotinic acid). The structures of the two complexes BrCo(dpgH)2(p-aminobenzoic acid) and BrCo(dpgH)2(isonicotinic acid) have been characterized by crystallographic technique. The density functional theory (DFT) studies have been carried out for two complexes ClCo(dpgH)2(p-aminobenzoic acid) (2) and BrCo(dpgH)2(p-aminobenzoic acid) (6). The cyclic voltamograms (CV) of all the complexes show an irreversible Co(III)/Co(II) reduction peak and a quasi-reversible Co(II)/Co(I) reduction peaks. All the synthesized complexes show the electrocatalytic behavior towards hydrogen evolution reaction using acetic acid as the proton source. The rate constants determined using FOWA analysis provides the highest rate constant of 1.7 × 106 mol-1s−1 for the complex (2).