Palladium(II) complexes with N-alkyliminodiacetic acid derivatives: Preparation, structural and spectroscopic studies

Abstract

The reactions of N-alkyl derivatives of iminodiacetic acid, RN(CH2COOH)2 (i-PridaH2 and t-BuidaH2; i-Pr=isopropyl, t-Bu=tert-butyl) with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Four new palladium(II) complexes {[Na[PdCl(i-Prida)](H2O)2]·1/2H2O}n (1), [Na[PdCl(t-Buida)](H2O)2]n (2), [Pd(i-PridaH)2]·2H2O (3) and [Pd(t-BuidaH)2] (4) were obtained and characterized by X-ray crystallography, infrared spectroscopy, 1H and 13C NMR spectroscopy, UV–Vis spectroscopy and thermal analysis (TG/DTA). In the solid state, the palladium(II) ion has square-planar coordination in all four complexes, composed of an O,N,O′-tridentate iminodiacetate ligand and a chloride ion in 1 and 2 and of two N,O-bidentate hidrogeniminodiacetate ligands in 3 and 4. Moreover, 1 is 2D coordination polymer composed of sodium ion clusters bridged by [PdCl(i-Prida)]− moieties, 2 is 1D coordination polymer composed of a zig-zag chain of sodium ions bridged by [PdCl(t-Buida)]− moieties and water molecules, while complexes 3 and 4 are monomeric species. Substitution of the chloride ligands in [PdCl(i-Prida)]− and [PdCl(t-Buida)]− by water molecules takes place after dissolution of the complexes 1 and 2, leading to formation of [Pd(i-Prida)(H2O)] (1′) and [Pd(t-Buida)(H2O)] (2′) species. Spectrophotometric potentiometric titration revealed that [PdCl(i-Prida)]− and [PdCl(t-Buida)]− are stable in acidic aqueous solution in the pH range 3–6 in the presence of chloride ions at [Cl−]>0.1M. Complexes 3 and 4 partially decompose upon dissolution in dimethyl sulfoxide, giving mixtures of the original complexes and by-products whose NMR spectra resemble those of 1′ and 2′. Antibacterial and antitumor properties of the water-soluble complexes 1′ and 2′ were also investigated.