Study of the NpO

Russian Journal of Coordination Chemistry (Impact Factor: 0.63). 01/2005; 31(11):804-808.

ABSTRACT 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) Å3, R = 0.048, wR(F
2) = 0.054. The crystal structure of the compound is composed of the [(NpO2)(CrO4)(H2O)]
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.

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