IR spectroscopic investigation of the structure of polymeric uranyl di(2-ethylhexyl)phosphate molecules in C6H6 and CCl4 solutions

Abstract

Using IR spectroscopy, we studied the types of coordination of POO groups in di(2-ethylthexyl)phosphate anionx X− with UO 2 2+ cations in the C6H6 and CCl4 solutions of the polymer molecules (UO2X2)p. The polymers exhibit tridentate-bridge coordination (I), which is not typical of (MXn)p salts Open image in new window where the phosphoryl oxygen atom forms two bonds with U(VI) atoms. When a few U(VI) atoms (≳7%) interact with donar additives, all POO group I change their coordination to the usual bidentate-bridge type, Open image in new window , resulting in a structural transformation of the polymer. The bridging POO group are responsible for the difference in the dimerization and trimerization constants and the constants of the subsequent addition of the monomer molecules UO2X2 to the polymer chain (UO2X2)p. It is suggested that type I coordination of X− to U(VI) is due to an extended bond between the 2p2-electrons of the phosphoryl oxygen atom of the X− anion and a vacant f-orbital of the U(VI) atom (pπ−fπ interaction). This unusual type of bond between uranium (VI) and tributyl phosphate (TBP) phosphoryl oxygen was found earlier for the UO2Cl2·2TBP complex.