An approach to the structure and spectra of copper barbiturate trihydrate

In the neutral title complex [Cu(C4N2H3)(2)(H2O)(3)] or [Cu(BBR)(2)(H2O)(3)] (BBR- = Barbiturate), the Cu-II ion, in the slightly distorted square-pyramidal geometry, is coordinated by two O atoms of the two monodentate barbiturates and three O atoms of three water ligands. The average bond length of Cu-O (BBR-) is 1.981(5) Angstrom and the average bond length of Cu-O (H2O) at the basal sites is 1.94(5) Angstrom, i.e. much shorter than that of Cu-O (H2O) [2.175(11) Angstrom]. The crystal structure is characterized by an extensive network of hydrogen bonds in which each [Cu(BBR)(2)(H2O)(3)] entity links to six adjacent [Cu(BBR)(2)(H2O)(3)] by O(C=O) ... H-O(H2O) bonds. Tautomerism in the coordination process for BBR- was found from the crystal structure and i.r. spectral analysis. The interaction of Cu-II and BBR- in aqueous solution was also investigated by electronic spectra and electrochemical method. It was observed that the copper ion could not only form the [Cu(BBR)(2)(H2O)(3)] complex in aqueous but also catalyze the decomposition of BBR- at pH 1.1.