Mercaptoethanesulfonic acid (CoM imitator) interaction studies with nickel(II) complexes of pyridyl groups containing tetradentate ligands: Synthesis, structure, spectra and redox properties

Nickel(II) complexes of N,N′-dimethyl-N,N′-bis(pyridyl-2yl-methyl)ethylene-diamine (L1), N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,2-diaminopropane (L2) and N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,3-diaminopropane (L3) were prepared and their spectroscopic and redox properties studied. The distorted octahedral structure was determined for [NiL3ClCH3OH](ClO4) by using X-ray crystallography. The electronic spectral behavior of the complexes at different pHs was analyzed; it is shown that a new band grew at the expense of the other band intensity in acid media. The redox properties of ligands and their complexes show the peaks of Ni(II) → Ni(III) and Ni(II) → Ni(0) as these were detected at low concentration while Ni(II) → Ni(I) process was detectable clearly at high concentration. Furthermore, the interaction studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN4 chromophores are discussed.

The protonation and the oxidation sites of ligands were identified by NMR and electrochemical methods. For nickel(II) complex of L3, a distorted octahedral structure was determined. The electronic spectra of the nickel complexes at different pHs reveal that a new band grew at the expense of the other band intensity in acid media. In the electrochemistry, the Ni(II) → Ni(III) and Ni(II) → Ni(0) are clearly observed at low concentration while Ni(II) → Ni(I) process was seen clearly at high concentration. Furthermore, the interaction of 2-mercaptoethanesulfonic acid as a CoM simulator with NiN4 chromophores were discussed.Figure optionsDownload as PowerPoint slide