A structural study on uranyl (VI) nitrate complexes with cyclic amides: N- n-butyl-2-pyrrolidone, N-cyclohexylmethyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidone

Abstract

Structural analyses of UO 2(NO 3) 2L 2 [L = N- n-butyl-2-pyrrolidone (NBP), N-cyclohexylmethyl-2-pyrrolidone (NCMeP), and 1,3-dimethyl-2-imidazolidone (DMI)] have been carried out using X-ray diffraction method. These uranyl complexes were found to have a hexagonal bipyramidal structure. The bond distances (Å) of U O and U–O(ligand), and bond angles (°) of U–O–C(carbonyl) are determined as follows: 1.774(2), 2.374(2), and 137.6(2) for UO 2(NO 3) 2(NBP) 2; 1.770(1), 2.383(2), and 135.3(1) for UO 2(NO 3) 2(NCMeP) 2; 1.771(2), 2.361(2), and 143.3(2) for UO 2(NO 3) 2(DMI) 2. In uranyl nitrate complexes with cyclic amides such as 2-pyrrolidone, urea, and caprolactam derivatives, a linear correlation was found to hold between U–O(ligand) bond distances and U–O–C(carbonyl) bond angles. Vibrational frequencies of UO 2(NO 3) 2L 2 have also been measured by IR and Raman spectrophotometers. Using relationships between vibrational frequencies of O U O bonds and donor numbers (DNs) of ligands, it was found that donicities of N-substituted-2-pyrrolidones (Me, Et, Bu, cyclohexyl, and cyclohexylmethyl) are in the range of 26–29, and the DN of 1,3-dimethyl-2-imidazolidone was estimated as 27.8.