Trends in the Electronic Structure and Chemical Bonding of a Series of Porphyrinoid-Uranyl Complexes.

In this paper, we have explored the relativistic density functional theory study on a series of deprotonated porphyrinoid (L n ) complexes of uranyl to investigate the geometrical structures and chemical bonding. The ligands bound with uranyl in the 1:1 complexes [UO 2 (L n )] x ( n = 4, 5, 6; x = 0, -1, -2), showing more thermodynamic stability for "in-cavity" structures of L 5 and L 6 than that of the "side-on" structure of L 4 and an increase in stability with the increase of negative charges, L 2- < L 3- < L 4- . Among the six ligands, the cyclo[6]pyrrole presents the best selectivity toward uranyl. Based on chemical bonding analyses, the U-N L bond in the in-cavity complexes adopts a typical dative N L → U bond with mainly ionic bonding and significant covalency, which comes from the significant orbital interaction of U 5f ϕ 6d δ 7s hybrid AOs and N L 2p-based MOs. This work provides a systematic understanding of the coordination chemistry in uranyl pyrrole-containing macrocycle complexes and the nature of chemical bonding in such systems, which may provide inspirations for the future design of synthetic targets that could be relevant to actinide separations or in the remediation of spent nuclear fuel.