Role of Electronegative Atom Present on Ligand Backbone and Substrate Binding Mode on Catecholase- and Phosphatase-Like Activities of Dinuclear Ni^II Complexes: A Theoretical Support

The reaction of two pentadentate compartmental ligands HL¹ and HL² [HL¹=2,6-bis((E)-(2-morpholinoethylimino)methyl)-4-tert-butylphenol; HL²=2,6-bis((E)-(2-(piperidin-1-yl)ethylimino)methyl)-4-tert-butylphenol] with nickel acetate followed by addition of NaSCN afforded two discrete dinuclear complexes, [Ni₂L¹(CH₃COO)₂(SCN)]^.(H₂O)₂ ^.(0.5CH₃OH) (1) and [Ni₂L²(CH₃COO)(SCN)₂(CH₃OH)]^.(CH₃OH) (2). Single crystal structure reveals that the complexes are Ni^II dimer with triple-mixed phenoxo and acetate/isothiocyanate bridges. Variable-temperature (3-300 K) magnetic studies have been performed and data analyses reveal that the dinuclear nickel(II) units show a weak ferromagnetic coupling in complex 1 (J=+ 3.70) and a weak antiferromagnetic coupling in complex 2 (J=- 0.87 cm^{– 1}). The catalytic promiscuity of the complexes in terms of two different bio-relevant catalytic activities like oxidation (catecholase) and hydroxylation (phosphatase) has been thoroughly explored. Role of an auxiliary electronegative atom present on the ligand backbone and binding approach of the substrate to the metal centres during the catalytic activities have been scrutinized by DFT calculation. Several experimental techniques have been utilised to evaluate the mechanistic interpretation of catecholase like activity. And finally, mechanistic pathway of both the bio activities are demonstrated.