Nickel and copper complexes of a new multidentate ligand: synthesis, characterization and magneto-structural investigations.

The ligand LH8Cl2 (LH6·2HCl) [(3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene)]pyridine-2,6-dicarbohydrazide dichloride] was prepared from the Schiff base condensation of pyridine-2,6-dicarbohydrazide with pyridoxal hydrochloride in methanol. Reaction of LH6·2HCl with CuCl2·4H2O or Cu(ClO4)2·6H2O in a MeOH/water mixture produced two 1-D copper coordination polymers with formulae {[Cu3(LH4)Cl3(H2O)]Cl·H2O}n (1) and {[Cu3(LH4)Cl(H2O)2(ClO4)][ClO4]2·2H2O}n (2) respectively. Similarly, reaction of LH6·2HCl with NiCl2·6H2O, Ni(ClO4)2·4H2O or Ni(NO3)2·6H2O afforded the trimetallic complex [Ni3(LH4)(H2O)9]Cl4·4H2O (3), the 1-D polymer {[Ni3(LH4)(NO3)(H2O)6](NO3)2·H2O}n (4) and [Ni2(LH6)(H2O)6](ClO4)4·3H2O (5). The crystal structures of 1-5 were determined by X-ray diffraction. All complexes 1-4 exhibit the same geometric arrangement of the ligand with the central metal linked to the terminal metal ions by a trans-diazine linker with the diazine and pyridoxal arms coordinating in a tridentate NO2 donor fashion, while the central metal atom is coordinated by the ligand in a tridentate fashion by the pyridine and two diazine-N atoms. Water and coordinating anions complete the coordination environment around the Cu2+ and Ni2+ ions. The ligand adopts the same geometry in 5 but is not deprotonated and does not possess a central metal atom. Magnetic measurements (5-300 K) reflect strong antiferromagnetic exchange across the 1,2-diazine bridge.