Synthesis, characterization and crystal structure of square-pyramidal copper(II) complexes with pyridoxylidene aminoguanidine

The synthesis of pyridoxylidene aminoguanidine hydrogenchloride hydrogennitrate (PLAG·HCl·HNO3), as well as the synthesis, physico-chemical characterization and crystal structure of two Cu(II) complexes with this ligand, of the formulas [Cu(PLAG)py(NO3)]NO3 (1) and [{Cu(PLAG)py}2](NO3)4 (2) are described. The X-ray analysis showed that Cu(II) is situated in a distorted square-pyramidal environment. In 1 PLAG is coordinated as usually, through the oxygen atom of the deprotonated phenolic OH group and nitrogen atoms of the azomethine and imino groups of the aminoguanidine fragment. In particular, in the centrosymmetric dimeric complex 2, besides the mentioned ligators, the oxygen atom of the hydroxymethyl group of the pyridoxal moiety is involved in coordination as the bridging ligator, connecting the subunits. This is the first dimeric complex with this ligand where the tetradentate coordination mode is observed. Voltammetric characteristics of the ligand and complexes 1 and 2 as well as [Cu(PLAG)Cl2] were investigated and reaction pathways including monomer–dimer equilibria established.