Use of acid–base and redox chemistry to synthesize cobalt(III) and iron(III) complexes of a partially deprotonated triprotic imidazole-containing Schiff base ligand: Hydrogen bound 1D linear homochiral and zig-zag heterochiral supramolecular complexes

Aerial reaction of cobalt(II) perchlorate with H3(1) [H3(1) is the tripodal ligand derived from the condensation of tris(2-aminoethyl)amine with three equivalents of imidazole-2-carboxaldehyde] in methanol and [FeH3(1)(ClO4)2] with Fe(1) in acetonitrile results in the formation of [CoH2L](ClO4)2·H2O and [FeHL]ClO4·CH3CN, respectively. Mössbauer spectroscopy and variable temperature magnetic susceptibility indicate that [FeHL]ClO4·CH3CN is a low spin iron(III) species. Both complexes were characterized by EA, IR, and single crystal structure determinations. Both complexes crystallize in the centrosymmetric monoclinic space group, P21/c, so both enantiomers of the chiral complex are present. The supramolecular features of these complexes, caused by the partial deprotonation of the ligand and the resultant formation of imidazole–H···imidazolate hydrogen bonds, are different. [FeHL]+ forms hydrogen bonds with molecules from adjacent cells of like chirality. This results in a linear homochiral array of iron complexes. In contrast, [CoH2L]2+ forms hydrogen bonds with a molecule from the same cell and one from another cell resulting in an 1D alternating heterochiral zig-zag chain.

The syntheses of M(III) (M = Fe or Co) partially deprotonated complexes of the triprotic Schiff base ligand, H3L, formed from the condensation of tris(2-aminoethyl)amine with imidazole-2-carboxaldehyde is achieved through acid–base and redox chemistry. [FeHL]+ and [CoH2L]2+ exhibit imidazole–H···imidazolate hydrogen bound 1D linear and zig-zag supramolecular complexes, respectively.Figure optionsDownload as PowerPoint slide