Preparation and study of amino acid (DL-leucine, L-isoleucine, L-histidine) Schiff bases with ethyl-α-ketocyclopentylcarboxylate and the corresponding copper(II) complexes

Abstract Amino acid Schiff bases with ester function K(Rleu)·2H 2 O ( 1 ), K(Rile)·2H 2 O ( 2 ), K(Rhis)·H 2 O ( 3 ) (Rleu, Rile and Rhis represent the Schiff base of DL -leucine, L -isoleucine and L -histidine, and ethyl-α-ketocyclopentylcarboxylate) were synthesized. Compounds 1 , 2 and 3 were characterized by 1 H NMR spectroscopy. The copper(II) complexes, Cu(Rleu′)·H 2 O ( 4 ), Cu[Rile′]·H 2 O ( 5 ) andCu(Rhis′)·2H 2 O ( 6 ), were obtained with the N-deprotonated Schiff bases (Rleu′, Rile′ and Rhis′). The COO stretching bands in their IR spectra suggest that the carboxylate acts as a monodentate group when binding with copper. The temperature dependence of the susceptibility for 6 may be fit to the Curie-Weiss expression χ=O.32/(T-26.2) emu mol −1 K −1 The dehydration process of 6 leads to the anhydrous compound, enthalpy (53±2kJ mol −1 ) and activation energy (82±5 kJ mol −1 ).