Photophysical, electrochemical and TD-DFT studies of Ni(II) and Mn(II) complexes of N′-(2-methylfuran-3-carbonyl)hydrazine carbodithioic acid ethyl ester

Abstract

Two new complexes [Ni(Hmfchce)2(py)2] (1) and [Mn(Hmfchce)2(o-phen)] (2) with [N′-(2-methylfuran-3-carbonyl)hydrazine]-carbodithioic acid ethyl ester (H2mfchce) have been synthesized which contain o-phenanthroline (o-phen)/pyridine (py) as coligand. The ligand and its metal complexes have been characterized by elemental analyses, IR, magnetic susceptibility and single crystal X-ray diffraction data. Complexes 1 and 2 crystallize in orthorhombhic system with space group ‘Pbca’ and ‘Pbcn’, respectively. In complex 1, nickel centre is coordinated through one hydrazine nitrogen atom, one carbonyl oxygen of two units of ligand and two pyridine nitrogen atoms. The manganese center in complex 2 is coordinated in a N4O2 core by two uininegative bidentate ligands using hydrazine nitrogen (after loss of proton) and carbonyl oxygen and two nitrogen atoms of o-phen. In both complexes, the metal ion adopts a distorted octahedral geometry. Complexes 1 and 2 are fluorescent materials which exhibit an emission at 291 and 285 nm, respectively upon excitation at 263 and 251 nm. The course of the thermal degradations of complexes 1 and 2 have been investigated by TGA which indicate that metal oxide is formed as the final residue in both complexes. The metal complexes, [Ni(Hmfchce)2(py)2] (1) and [Mn(Hmfchce)2(o-phen)] (2) were immobilized on glassy carbon electrodes using Nafion® (Nf). The modified electrodes have been characterized by cyclic voltammetry in 0.1 M KOH. Complexes 1 and 2 have efficient activity towards electrochemical water oxidation in the 0.1 M KOH. The simulated spectra of the two complexes 1 and 2 are characterized by excited states with ligand-to-ligand charge-transfer (LLCT) and ligand-to-metal charge-transfer (LMCT) character.