Synthesis, structural, spectroscopic, thermal and voltammetric properties of 5,5-diethylbarbiturato complexes of zinc with 2-(2-aminoethyl)pyridine and 2-(2-hydroxyethyl)pyridine

Abstract

Two new bis(5,5-diethylbarbiturato) (barb) complexes of zinc, [Zn(barb)2(aepy)j (1), [Zn(barb)2(hepy)] (2) [aepy = 2-(2-aminoethyl)pyridine and hepy = 2-(2-hydroxyethyl)pyridine], have been prepared and characterized by elemental analysis, FT-IR spectroscopy, thermal analysis and single crystal X-ray diffraction. Complex I crystallizes in the triclinic Pi space group; crystals of complex 2 could not be obtained. The zinc(II) in complex I is tetrahedrally coordinated by two barb and an aepy ligand. The barb ligands are N-coordinated while the en ligand acts as a bidentate N,N ' chelate. One of the carbonyl oxygen atoms of each barb ligand makes a remarkably long bond to zinc and in this case, coordination geometry can be considered as a highly distorted octahedron. The molecules of complex I are connected via N-H center dot center dot center dot O hydrogen bonds, involving hydrogen atoms of both barb and aepy ligands. The voltammetric behavior of complexes I and 2 was investigated in aqueous solution by cyclic voltammetry using a NH3/NH4C] buffer. The cyclic voltammograms of both complexes are similar, showing well-defined cathodic and anodic peaks at -1.29 and -1.10V, respectively, due to a quasi-reversible two-electron transfer of the complexed zinc(II) ions.