SYNTHESIS, SPECTRAL AND STRUCTURAL STUDIES ON METAL-COMPLEXES OF SCHIFF-BASES INVOLVING VITAMIN-B6 AND HISTAMINE

Six metal complexes of Schiff bases involving Vitamin B6 and the decarboxylated amino acid histamine have been synthesised and characterized. Crystal structures have been determined for [CuL1(H2O)Br]NO3 1 (L1 = pyridoxylidenehistamine) and [Cu2L2(2)(NO3)2].6H2O 2 (L2 = 5'-phosphopyridoxylidene-histaminate). The crystal structure of complex 1 [space group P1BAR, a = 8.161(2), b = 10.368(2), c = 11.110(2) angstrom, alpha = 105.18(1), beta = 102.12(1), gamma = 72.10(1)-degrees and Z = 2; R = 0.072, R' = 0.083] consists of square-pyramidally co-ordinated copper with the tridentate Schiff base in the zwitterionic form, whereas in 2 [space group P1BAR, a = 8.727(1), b = 10.308(1), c = 12.845(2) angstrom, alpha = 110.00(1), beta = 78.94(1), gamma = 114.35(1)-degrees and Z = 1; R = 0.035, R' = 0.034] the copper has the same co-ordination geometry but the tetradentate Schiff-base ligand exists as a monoanion. The conformational parameters deduced from such structures are important for understanding the stereochemical aspects of Vitamin B6-catalysed model reactions involving histidine.