ELECTRONIC ABSORPTION-SPECTRA OF SOME NEPTUNIUM(IV) BETA-DIKETONATES

Electronic absorption spectra of eight-coordinate Np(IV) beta-diketona te complexes are discussed. Acetylacetone (Hacac), dibenzoylmethane (H dbm), benzoylacetone (Hbac), benzoyltrifluoroacetone (Hbtfa), and then oyltrifluoroacetone (Htta) were selected as P-diketones. Structural fe atures of the Np(IV) complexes were discussed using data for the U(IV) and Th(IV) analogs. The spectra of crystalline Np(IV) B-diketonates c an be subdivided in two groups depending on the coordination polyhedro n of the central atom, tetragonal antiprism [Np(acac)(4), Np(dbm)(4), and Np(dbm)(4), or bitetrahedron [Np(bac)4, Np(btfa)(4)]. In the case of a nearly ideal square antiprism the maximum of the characteristic l ong-wave absorption band is at about 980 nm; deviation from the ideal structure is accompanied by its shift to 990 nm. On passing to the bit etrahedron, the maximum shifts to 1003 nm. The spectra of the Np(IV) B -diketonates studied in benzene solutions are similar and resemble tho se of the crystalline compounds of the first group. Apparently, on dis solution of Np(lV) beta-diketonates in benzene the bidentate ligands a re oriented around the central atoms to form a tetragonal bipyramid of the oxygen atoms.