Synthesis, crystal structures and electrocatalytic water oxidation by Mn(II), Co(II) and Ni(II) complexes of thiophene-2-carbohydrazide

•Synthesis and Characterization of Thiophene-2-carbohydride based metal complexes.•Crystal structures of Mn(II), Co(II), and Ni(II) complexes.•Metal complexes show significant OER activity at lower onset potentials.•Complexes 2 and 3 have tafel slope of 45.7 and 41.5 mV/decade.•Comparative study with previous and benchmark electrocatalysts. Electrocatalytic water oxidation by molecular electrocatalyst has emerged very rapidly. Here, metal complexes of Mn(II), Co(II), and Ni(II) containing Thiophene-2-carbohydrazide were synthesized and characterized by spectroscopic and single crystal X-ray techniques. The complexes 1, 2, and 3 crystallize in monoclinic, orthorhombic, and monoclinic systems with space groups P21/c, Pca21, and P21/c, respectively. The crystal structure of complexes is stabilized via various intermolecular hydrogen bonding including N-H···Cl, O-H···Cl, O-H···O, N-H···O, C-H···S etc. providing supramolecular architectures. The prepared metal complexes [Mn(tphch)3]2+ (1), [Co(tphch)3]2+(2), and [Ni(tphch)3]2+(3) were coated on glassy carbon electrodes (GCE). Nafion (Nf) solutions were used during the immobilization process to provide an electroactive surface on GCE (GCE/Nf). Electrochemical characterizations of modified electrodes were achieved from the results of cyclic voltammetry and linear sweep voltammetry techniques. GCE modified GCE/Nf/Complex-1, GCE/Nf/Complex-2, and GCE/Nf/Complex-3 show efficient electrocatalytic activity for oxygen evolution reaction (OER). Tafel slope of GCE/Nf/Complex-2 and GCE/Nf/Complex-3 was found lower than commercial benchmark electrocatalyst RuO2 and IrO2. [Display omitted]