CRYSTAL AND MOLECULAR-STRUCTURE OF NEPTUNYL MALONATE TRIHYDRATE (NPO2)2C3H2O4.3H2O

The single-crystal x-ray structure of (NpO2)2C3H2O4.3H2O (I) is solved (Siemens P3/PC, graphite monochromator, Mo Kalpha-radiation). ne unit -cell parameters are a = 6.596(1), b = 8.320(1), c = 10.308(2) angstro m, beta = 90.24 (2)-degrees, Z = 2, space group P2(1), d(calc) = 4.07 g/cm3, 2239 reflections with I > 3sigma(I), R = 0.049, R(w) = 0.073. T he crystal structure of I is constructed of NpO2+, C3H2O42-, coordinat ed water, and water of crystallization. The two crystallographically u nique NpO2 groups (Np coordination number 7, pentagonal bipyramidal co ordination polyhedron) are joined into planar ''square'' cationic netw orks in which both groups act as bidentate ligands. The malonate ion a dditionally joins Np atoms of one network that are bonded to each othe r by cation - cation (CC) interactions. The structure of I is compared to that of the previously described (NpO2)2C3H2O4.4H2O (II). The chan ge from II (crystallized in the cold) to I (crystallized from hot solu tions) is accompanied by the exclusion of water from the Np coordinati on sphere and produces a structure rearrangement with formation of new CC bonds.