Mercaptoethanesulfonic acid studies with nickel(II) complexes of tetra- and hexadentate ligands containing pyridyl groups: synthesis, structure, spectra and redox behavior

Abstract

Nickel(II)complexes of N, N, N′ N′-tetrakis(2-pyridylmethyl)ethylenediamine (L 1), N, N, N′ N′-tetrakis(2-pyridylmethyl)-1,2-diaminopropane (L 2), N, N, N′ N′-tetrakis(2-pyridylmethyl)-1,3-diaminopropane (L 3), N, N′-bis(2-pyridylmethyl)ethylenediamine (L 4), N, N′-bis(2-pyridylmethyl)-1,2-diaminopropane (L 5) and N, N′-bis(2-pyridylmethyl)-1,3-diaminopropane (L 6) were prepared and their spectroscopic and redox behaviors studied. The distorted octahedral geometry was determined for [NiL 2](ClO 4) 2 by using X-ray crystallography. The electronic spectral bands ( 3A 2g→ 3T 2g and 3A 2g→ 1E g transitions) of NiN 6 and NiN 4O 2 were analyzed; it shows that the former complexes possess well-resolved bands compared to the latter compounds. In addition, the ligand field parameter Dq found for NiN 4O 2 complexes was much lower than that of NiN 6 compounds; thereby, a more positive redox potential was detected for NiN 4O 2 complexes in electrochemistry over the NiN 6 compounds. Further, the coordination studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN 4 or NiN 6 chromophores were discussed.