Study of the NpO

A new neptunium(VI) complex (NpO₂)(CrO₄)(H₂O)] ⋅ 4H₂O (I) was synthesized, its crystal structure was determined, and the IR and near-IR absorption spectra were measured. The unit cell parameters are: a = 8.634(4) Å, b = 11.119(4) Å, c = 9.410(3) Å, β = 92.40(3)°, space group P2₁/c, Z = 4, V = 902.6(6) ų, R = 0.048, wR(F ²) = 0.054. The crystal structure of the compound is composed of the (NpO₂)(CrO₄)(H₂O)] _n layers and the crystal water molecules located between the layers. The coordination polyhedron of neptunium is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two bridging water molecules and three chromate ions. The Np(VI) complexation with the chromate ions in an aqueous solution at μ = 1 was studied by spectrophotometry. The stability constants for 1 : 1 and 1 : 2 complexes were calculated, logβ₁ = 3.19(2), logβ₂ = 3.93(2), respectively. __________ Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 11, 2005, pp. 848–852. Original Russian Text Copyright ? 2005 by Budantseva, Andreev, Fedoseev, Astafurova, Antipin.