Synthesis, characterization, molecular structure and self-assembly of some cobalt(III) complexes derived from diacetyl- and benzil bisaroylhydrazones

Abstract

Cobalt(III) complexes of the general formula [Co(HL1–R)(L1–R)], [Co(HL2–R)(L2–R)] and [Co(HL1–R)2]Cl, where H2L1–R and H2L2–R referred respectively to diacetyl and benzil bis(aroylhydrazone), have been prepared and characterized by IR, electronic, ESI and 1H NMR spectral measurements. The bisaroylhydrazone ligand in these complexes acts either as mononegative N2O tridentate, [HL1,2–R]−, or dinegative N2O tridentate, [L1,2–R]2−. Coordination occurs via the two diimine nitrogens and the deprotonated enolimine oxygen of one aroylhydrazone moiety, leaving the other one uncoordinated. The X-ray crystal structures of [Co(HL2–CH3)(L2–CH3)] and [Co(HL1–R)2]Cl (R=H, CH3) show that the molecular units are assembled into dimers through π–π stacking and hydrogen-bonded interactions respectively in the neutral and cationic complexes. Both types of dimers are linked together giving linear chains which in turn are interconnected to produce layers. These layers are further assembled with each other in [Co(HL2–CH3)(L2–CH3)] and [Co(HL1–H)2]Cl to generate three-dimensional frameworks, while in the cationic complex [Co(HL1–CH3)2]Cl, the molecular units form chains of dimers with a one-dimensional tubular structure.