Synthesis of new Cu(II), Ni(II) and Co(II) complexes with a bis-amide ligand functionalized with pyridine moieties: Spectral, magnetic and electrochemical studies

Three new copper(II), nickel(II) and cobalt (II) dinuclear complexes with a bis-amide ligand derived from tartaric acid have been prepared and characterized. For this purpose, the ligand (R,R)-(+)-di-N,N′-methylpyridino-tartramide (dmpt) was synthesized via the classical aminolysis of (R,R)-(+)-dimethyltartrate with pyridylmethylamine. The molecular structures of the complexes Na[Cu₂(dmptH₋₃)(CO₃)] · 8H₂O (1) and [Ni₂(dmptH₋₂)₂] · 9.75H₂O (2) were elucidated by X-ray diffraction, and the complex [Co₂(dmptH₋₃)(μ-OH)] · NaClO₄ · 5H₂O (3) by XAS. The crystal structure of (1) shows that the two metallic centres are in a square planar environment. Each copper(II) is bound to pyridyl and deprotonated amidic nitrogen atoms and to the oxygen atoms of hydroxyl and carbonato groups. In complex (2), both nickel atoms are in a distorted octahedral environment with an identical set of donors atoms, N₄O₂, coming from four nitrogen atoms of two pyridylmethylamido moieties and two oxygen donor atoms of alcohol groups. XAS analysis of complex (3) allows us to propose a CoN₂O₄ chromophore, with two nitrogen atoms coming from pyridyl and amidic groups and two bridged oxygen atoms from a deprotonated alcohol group and an hydroxyl group; the hexacoordination is achieved by two water molecules. The spectroscopic, electrochemical and magnetic properties of these complexes were investigated.