Structural diversity of benzil bis(benzoylhydrazone): Mononuclear, binuclear and trinuclear complexes

Abstract

The coordination behaviour of the Schiff-base, benzil bis(benzoylhydrazone), LH₂ towards divalent nickel, lead, cadmium, zinc and copper ions has been investigated. The complexes have been fully characterized by techniques including ¹¹³Cd and ²⁰⁷Pb NMR, as well as ¹³C and ¹¹³Cd CP/MAS NMR and by single crystal X-ray diffraction. All the complexes have the general formula [ML]_n (n = 1–3 depending on the metal ion), with the ligand doubly deprotonated. The nickel complex [NiL] 1 is a monomeric compound, the lead complex [PbL]₂2 shows a binuclear structure, whereas zinc [ZnL]₃4 and copper [CuL]₃5 complexes are trinuclear helicates. The cadmium 3 complex seems to be a dimer with a structure similar to that of 2. In the nickel 1 and lead 2 derivatives, the ligand behaves as a tetradentate N₂O₂ chelate and in complex 2 also as a bridge through one of the O atoms. In the crystal structures of Zn 4 and Cu 5 complexes [ML]₃ each metal is in a pentadentate N₃O₂ environment formed by two different ligands, one tridentate chelate and the other bidentate chelate, giving rise to trinuclear helicates. These results point out the versatility of benzil bis(benzoylhydrazone) on its coordination.