X-ray absorption near-edge spectroscopy of antimony complexed with organic molecules: a theoretical interpretation

Abstract

There are great concerns over the process of antimony complexation with organic ligands because it results in biotoxic compounds that are highly mobile in the environment. Structural resolution and pertinently quantitative analysis of those complexes in a diversified matrix is important, because they are crucial aspects to assess the possible environmental risk. X-ray absorption near-edge spectroscopy (XANES) is a promising method for resolving structure in a complicated matrix because of the wide-ranging sample status, strong structural sensitivity, and conspicuous spectral features. The obvious difference in the intensity of the shoulder peak at the white-line region was identified as one spectroscopic feature observed from two Sb(III) complexes with ligands of tartaric acid and EDTA. To decipher the structurally dependent XANES features of antimony complexes, time-dependent density functional theory (TD-DFT) was employed to simulate XANES and interpret the transitional nature of the white line. The theoretical XANES reproduced the shoulder feature. This shoulder feature was ascribed to the metal–ligand charge transfer (MLCT) transition from Sb 1s to the unoccupied states of the carbon chains. This transition was not favored due to the long distance between the ligand and metallic center in Sb(III)–EDTA, leading to a decrease in the shoulder peak. This study increased our understanding of XANES as a structurally dependent form of spectroscopy and highlighted the importance of the shoulder feature of the white line in XANES analysis.