Configurational, LFDFT and NBO analysis of chromium(III) complexes of edta-type ligands

Abstract

A new hexadentate chromium(III) complex, Na[Cr(1,3-pd3ap)]center dot 3H(2)O, containing an unsymmetrical edta-type ligand, the 1,3-propanediamine-N,N,N'-triacetate-N'-3-propionate ion (1,3-pd3ap), has been prepared, chromatographically separated and characterized. Only one [trans(O-5)] of the two possible geometrical isomers was isolated. In this isomer the two five-membered glycinate rings (R rings) occupy trans-axial sites, while the one glycinate ring and one beta-alaninate ring lie in the equatorial plane with the two diamine nitrogens (G rings). This result confirms the assignment made on the basis of Density Functional Theory (OFT), IR and UV-Vis spectral data analyses. The spectral data and electronic transition assignment, DFT-NBO, Ligand Field DFT and extensive strain analysis are discussed by a comparison with those of other [Cr(edta-type)](-) complexes of known configurations. The stoichiometry and stability of the complexes formed between the chromium(III) ion and 1,3-propanediamine-N,N,N'-triacetic-N'-propionic acid (H(4)1,3-pd3ap) were determined in aqueous solution by potentiometry at 25 degrees C and 0.1 M NaCl ionic strength. The existence of Cr(HnL), n = 0,1, 2 and 3 type complexes were verified. The formation of the Cr(OH)L complex was observed at higher pH values. The concentration distribution diagrams of the complexes were evaluated.