Supramolecular Co(II) complexes based on dithiolate and dicarboxylate ligands: Crystal structures, theoretical studies, magnetic properties, and catalytic activity studies in photocatalytic hydrogen evolution

Abstract

Two supramolecular Co(II)-based coordination compounds have been harvested from dithiolate and dicarboxylate ligands. They have been structurally characterized by FT-IR, elemental analysis, and single crystal X-ray diffraction. Salt 1 consists of two ([tris (2-aminoethyl) amine Co] 1,1-dicyano-2,2-ethylenedithiolate)+ per thiosulphate ion linked through intermolecular hydrogen bonds. Compound 2, (pyridine-2,6-dicarboxylate)2Co-5H2OCo).2H2O, is stabilized by intramolecular O−H···O hydrogen bonds, building ribbons that propagate along the [100] direction in the crystals. From HS analysis, it is observed that the major non-covalent interactions present in 1 are C−H···O, N−H···N, N−H···S, and N−H···O hydrogen bonds, which play an important role in stabilizing the crystal structure. In 2, out of all the non-covalent interactions, O···H/H···O interactions have major contributions to stabilize the crystal structure. Theoretical investigation on the molecular structures of the crystals also revealed that the major stabilizing factor for 1 is H-bonding along with π-π stacking while that for 2 is co-ordinate bond between water and cobalt(II) ion. Direct current variable-temperature magnetic susceptibility measurements carried out on polycrystalline samples of 1 and 2 in the temperature range of 1.8–300 K shows the presence of magnetic anisotropy of the cobalt(II) ion in 1 and weak intermolecular exchange in 2. Further, both the compounds 1 and 2 are found to be highly efficient water reduction catalysts in terms of per Co turn-over-numbers at lower concentrations.