Imidazole-based nickel(II) and cobalt(II) coordination complexes for potential use as models for histidine containing metalloproteins

It has been established that small molecule model complexes have been useful in studying more complex biological systems of metalloproteins. Because many metalloproteins have active sites that contain multiple histidine residues bound to a metal center, a series of imidazole-containing scorpionate ligands and the associated Co and Ni complexes have been developed to investigate the bonding parameters of histidine containing active sites. The tris(2-imidazolyl) carbinol (2-TIC, 6) and tris[2-(N-methylimidazolyl)] carbinol (2-MeTIC, 7) complexes of Ni2+ and Co2+, namely [Co(2-MeTIC)2]Cl2 (8), [Co(2-MeTIC)2](NO3)2 (9), [Ni(2-MeTIC)2]Cl2 (10), [Ni(2-MeTIC)2](NO3)2 (11), [Co(2-TIC)2](NO3)2 (12), and [Ni(2-TIC)2](NO3)2 (13), have been prepared from the reaction of the appropriate ligand and appropriate metal salt in polar solvent. These complexes have been characterized by single crystal X-ray diffraction, spectroscopic techniques, and magnetic susceptibility. In each solid-state structure the metal center in the cation coordinates to three N atoms from two ligands and adopts a pseudo-octahedral coordination geometry. The X-ray characterization of tris[2-(N-methylimidazolyl)] carbinol is also reported.