Neptunium(V) Isothiocyanate Complexes with 4′-Aryl-Substituted 2,2′:6′,2″-Terpyridines and N, N-Dimethylacetamide as Molecular Ligands

New complexes of neptunyl(V) isothiocyanate with 4'-aryl-substituted 2,2':6',2″-terpyridines (Terpy) and N,N-dimethylacetamide (DMA) were obtained: [(NpO2)(4'-Ph-Terpy)(DMA)(NCS)]·DMA, [(NpO2)(4'-(4-(CF3)C6H4)-Terpy)(DMA)(NCS)]·2H2O·DMA, [(NpO2)(4'-(3-BrC6H4)-Terpy)(DMA)(NCS)]·DMA, and [(NpO2)(4'-(2-(COOH)C6H4)-Terpy)(DMA)(NCS)]·DMA. The structures of the compounds were determined with X-ray diffraction analysis. The neptunium coordination polyhedra were found to be pentagonal bipyramids with O atoms of the NpO2 groups in the apical positions and the equatorial planes formed by three N atoms of the terpyridine ligand, a N atom of the isothiocyanate anion, and an O atom of DMA. The influence of the substituents of the Ar group on the crystal structure is discussed. The IR spectra contain well-resolved bands of characteristic vibrations of all groups in the complex. The electronic absorption spectra are typical for neptunium(V) complexes and contain an intense narrow absorption band belonging to an f-f transition with a maximum of 988 nm and several long-wave satellites of lower intensity. The substituted terpyridines were shown to be efficient for the extraction of various valence forms of neptunium from the isothiocyanate solutions.