Coenzyme M studies with nickel(II) compounds - Synthesis, structure, spectra and redox behaviors

Nickel(II) complexes of 1,6-bis(pyridyl)-2,5-dithiahexane (L-1), 1,7-bis(2' -pyridyl)-2,6-dithiaheptane (L-2) and 1,9-bis(2'-pyridyl)2,5,8-trithianonan e (L-3) have been prepared and their spectroscopic and redox behaviors were studied. [Ni(II)L-1 (H2O)(2)](ClO4)(2), and [Ni(II)L-3(H2O)](ClO4)(2) were crystallized in single crystal form; their structures were solved by X-ray crystallography. The structures of the complexes are of distorted octahedr al geometry. A red shift in the electronic spectra and a positive potential shift in electrochemical studies were detected during the addition of the sodium salt of 2-mercaptoethanesulfonic acid (CoM) to Ni(ll) complexes cont aining L-1 and L-2. The high redox potential shifting difference (PSD) was observed with the addition of CoM to [NiL1](2+), which accounts for the axi al coordination of CoM with the nickel ion. However, [Ni(II)L-3](2+) does n ot respond well with CoM addition due to the structural limitation around t he Ni(II) ion. A destabilization of [Ni(II)L-1](2+) and [Ni(II)L-2](2+) com plexes and stabilization for [Ni(II)L-3](2+) were noticed in their redox st udies and these trends were inversely changed during anaerobic CoM addition to Ni(II) complexes. A. nephelauxetic effect (beta values) has been shown to establish a good relation with PSD. (C) 1999 Elsevier Science Ltd. Ail r ights reserved.