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

Structural analyses of UO2(NO3)2L2 [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 Udouble bond; length as m-dashO 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 UO2(NO3)2(NBP)2; 1.770(1), 2.383(2), and 135.3(1) for UO2(NO3)2(NCMeP)2; 1.771(2), 2.361(2), and 143.3(2) for UO2(NO3)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 UO2(NO3)2L2 have also been measured by IR and Raman spectrophotometers. Using relationships between vibrational frequencies of Odouble bond; length as m-dashUdouble bond; length as m-dashO 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.