Synthesis and Characterization of Diaquo Bis( N – Histidyl - 2, 4 - Pentanedionato) Copper (II) Complex

Abstract

N – histidyl – 2, 4 – pentanedione Schiff base was prepared from the reaction of histidine and 2, 4 -pentandione. The reaction of methanolic solution of N – histidyl – 2, 4 – pentanedione Schiff base with ethanolic
solution of copper (II) chloride gave diaquo bis( N – histidyl - 2, 4 - pentanedionato) copper (II) complex. The prepared Schiff base is crystalline orange yellow, has a yield of 51% and melting point of 292oC. The prepared diaquo bis( N – histidyl - 2, 4 - pentanedionato) copper (II) complex is crystalline green, has a yield of 72% and decomposition
temperature of 345oC. The Schiff base is soluble in most solvent including water, but insoluble in ether. The diaquo bis( N – histidyl - 2, 4 - pentanedionato) copper (II) complex is soluble in water, DMSO and DMF, but insoluble in most common organic solvents. The molar conductance of copper (II) Schiff base complex determined is 31 ohm-1 cm2 mol-1. The infra-red spectral data showed bands in the range 1612 – 1634 and 1590 - 1610cm-1, assignable to v(C=N) stretching vibrations of Schiff base and its copper (II) complex, respectively. The broad bands in the range 3345 - 3470 and 3352 - 3431cm-1 are attributable to v(O-H) stretching frequencies in the Schiff base and it complex compound, respectively. The weak bands at 543 and 362 cm-1 are attributable to v(Cu-O) and v(Cu-N) stretching vibrations, respectively in the copper (II) Schiff base complex. The dissociation constant (pKa) of N – histidyl - 2, 4 - pentanedione Schiff base determined is 4.73. The stability constant and Gibb’s free energy of copper (II) Schiff base complex determined are 8.9x109 and -5.68x104 Jmol-1, respectively. The ratio of copper (II) ion to N – histidyl - 2, 4 -
pentanedione determined using potentiometer is 1:1