Pentakis(carbamide)dioxoneptunium(V) Nitrate [NpO2{OC(NH2)2}5](NO3): Synthesis, Crystal Structure, and Some Properties

X-ray diffraction and spectroscopic data for a new Np(V) compound, namely, [NpO2{OC(NH2)2}5](NO3) (I) are presented. Crystals are monoclinic, space group P21, a = 11.142(2) Å, b = 7.6379(9) Å, c = 11.143(2) Å, β = 108.9(1)°, Z = 2, V = 897.1(2) Å3. The neptunium atom has a typical pentagonal-bipyramidal environment with five oxygen atoms of the carbamide molecules in the equatorial plane. The nitrate ion is in the outer sphere. Carbamide is a strong molecular ligand with respect to Np(V) and hence, cation–cation bonds of the NpO2+ ions are not realized in structure I. The wave length of the f–f transition in the electronic absorption spectra of crystalline complex I and Np(V) in a saturated carbamide solution is virtually the same and is equal to 991 nm.