Conformations of the nonbonded and the coordinated ligand nonamethylimidodiphosphoramide (NIPA) in the solid state and in solution: x-ray structure determinations, NMR study, and theoretical calculations on the NIPA molecule and the complex [UO2(NIPA)2C2H5OH](ClO4)2

The structures of crystalline nonamethylimidodiphosphoramide (NIPA) and its uranyl complex as determined by x-ray diffraction are compared to results from NMR spectroscopy on solutions. It is shown that in solid NIPA the P=O groups are in a trans conformation whereas in polar solvents (CH2Cl2, CH3NO2) and in the complex they are in a cis arrangement. The total energies of the two conformations were calculated theoretically and a stabilization of ca. 10 kJ mol-1 was found for the cis conformation of NIPA when surrounded by a polar solvent. 31P-31P and 31P-15N coupling constants were equally calculated and agree well with the values determined experimentally