Biomimetic zinc(II) and cobalt(II) complexes with tri-tert-butoxysilanethiolate and imidazole ligands – Structural and spectroscopic studies

New, heteroleptic zinc and cobalt complexes with tri-tert-butoxysilanethiolate and imidazole co-ligands are characterized by crystal structure studies. The ligands exhibit different coordination modes to Co(II) ions: NOS2 (with methanol as O-donor ligand) in 2′, NO2S2 in 2′′, N2S2 in 1, and to Zn(II) ions: N2S2 in 3 and N3S in 4. Complex 2′ is a structural analog of cobalt-substituted active site of alcohol dehydrogenase. All four-coordinate Co(II) and Zn(II) complexes have tetrahedral geometry. Solution and solid state electronic spectra of cobalt(II) complexes are discussed and compared to literature data available for the cobalt-substituted liver alcohol dehydrogenase and sorbitol dehydrogenase. The EPR spectra of all cobalt complexes exhibit at 77 K a characteristic broad signal with g ∼3.6 and 5.6, strongly indicating a high-spin state, S = 3/2, of Co(II) complexes.

Graphical abstractNew, heteroleptic zinc and cobalt complexes with tri-tert-butoxysilanethiolate and imidazole co-ligands are characterized in solid state by crystal structure studies. Cobalt(II) complexes are further studied by solid UV–Vis and EPR spectroscopy. The ligand exchange processes for the cobalt(II) complexes dissolved in methanol are evidenced by electronic spectroscopy. Cobalt(II) complex with tri-tert-butoxysilanethiolate, 2-methylimidazole and methanol ligands is a structural analog of cobalt-substituted active site of alcohol dehydrogenase. A cationic zinc complex with three 2-ethylimidazole ligands and one thiolate ligand can serve as a model for the zinc-binding site in zymogen form of matrixins.Figure optionsDownload full-size imageDownload as PowerPoint slide