CRYSTAL-STRUCTURE AND ABSORPTION-SPECTRA OF SOME NEPTUNIUM(V) DECATUNGSTATES

Crystal structure of K4Na3H[NP(W5O18)(2)].16H2O (I) was determined usi ng a CAD-4 autodiffractometer (MoKalpha radiation, graphite monochroma tor, omega/2 theta scanning, 2 theta(max)60 degrees). Crystal data: a = 18.862(4), c = 28.233(5) Angstrom, V = 10045(3) Angstrom(3), space g roup P4/ncc, Z = 8; R = 6.27% and R-W = 6.61% from 2997 independent re flections with I > 4 sigma(I). The principal structural units are hete ropoly anions (HPA) [Np(W5O18)(2)](8-) linked by alkali metal cations and water molecules into a three-dimensional skeleton. The packing is additionally stabilized with hydrogen bonds. The coordination polyhedr on (CP) of Np atom is a nearly ideal square antiprism. The structure o f Na-8[Np(W5O18)(2)]. 3OH(2)O (II) is discussed in comparison with iso structural Na-8[UW10O36]. 3OH(2)O (III) studied previously. The struct ures of HPAs and CPs of central atoms in both compounds are noted to b e very similar. Insignificant distortions of CP are caused by effects of outerspheric cations and hydrogen bonds. Electronic absorption spec tra (EASs) of crystalline I and II were studied. It was found that the spectra are identical. Distortions of oxygen surrounding of the Np4ion are not manifested in EASs. In passing from EASs of solids to EASs of aqueous solutions, the peak positions and relative intensities do not vary. This suggests that the oxygen surrounding of central atoms i n the form of a square antiprism is preserved in aqueous solutions.