Preparation of Chromium(III) and Cobalt(III) Complexes with d,l-α-Phenylalanine-N,N-diacetic Acid

Abstract

Abstract The following chromium(III) and cobalt(III) complexes with PADA (d,l-α-phenylalanine-N,N-diacetic acid) were prepared: K[Cr(OH)pada(H2O)]·5H2O (violet) (I), K[Cr(OH)pada(H2O)2]·3H2O (green)(II), (enH2)1⁄2[Cr(OH)pada(H2O)2] (green) (III), [Cr pada(o-phen)]·H2O (brown) (IV), K2[Cr(ox)pada]·2H2O (violet) (V), K[Co(OH)pada(H2O)]·5H2O (blue-violet) (VI), and K2[Co2(OH)2(pada)2] (brown-pink) (VII). On the basis of electronic spectra in both aqueous solution and solid state, it was found that PADA behaves toward central metal as a quadridentate ligand in complexes I, IV, V, VI, and VII; in other words, unlike the case of nitrilotriacetic acid (NTA), nitriloisopropionicdiacetic acid (NIPDA) and l-leucine-N,N-diacetic acid (LDA), PADA did not give different coordinating structures to the respective complexes in solid state and aqueous solution. From thermal analysis with derivatograph in the reaction processes of complex VI, it was found that the complex liberates one mole of coordinating water at about 170–180°C, resulting in the formation of the diol complex VII.