New heteroleptic [Ni(ii) 1,1-dithiolate-phosphine] complexes: synthesis, characterization and electrocatalytic oxygen evolution studies

Abstract

Four new heteroleptic Ni(II) complexes with general formula [Ni(II)(LL′)] (L = 2-(methylene-1,1′-dithiolato)-5-phenylcyclohexane-1,3-dione (L1) and 2-(methylene-1,1′-dithiolato)-5,5′-dimethylcyclohexane-1,3-dione (L2); L′ = 1,2-bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)monosulphide methane (dppms) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR). All complexes 1–4 have also been characterized by PXRD and single crystal X-ray crystallography. The solid state molecular structures revealed distorted square planar geometry about the four-coordinate Ni(II) metal centre together with rare Ni⋯H–C intra/intermolecular anagostic interactions in axial positions. In these complexes supramolecular structures have been sustained by non-covalent C–H⋯O, C–O⋯H–O, C–H⋯π, C–H⋯π (NiCS₂, chelate), π⋯π and H⋯H interactions. Their electrocatalytic properties have been investigated for oxygen evolution reaction (OER) in which complex 2 showed the highest activity with 10 mA cm⁻² at the potential of 1.58 V vs. RHE. In addition, complex 2 also exhibits an OER onset potential at 1.52 V vs. RHE.