SYNTHESIS, CRYSTALLIZATION AND MOLECULAR-STRUCTURE OF CRYSTAL HYDRATES OF THE COMPLEX NEPTUNIUM(V) OXALATE [CO(NH3)6][NPO2(C2O4)2]NH2O(N=3,4)

The compounds [Co(NH3)6][NpO2(C2O4)2].nH2O [n = 3 (I), 4 (II)] were pr epared by adding Co(NH3)6Cl3 to an oxalate solution of Np(V). Conditio ns were determined for predominant separation of I or II as single cry stals. The x-ray data were collected on a CAD4 diffractometer. The coo rdination polyhedra of Np (pentagonal bipyramid) in the centrosymmetri c dimeric complex anion of I [NpO2(C2O4)2]2(6-) have a common edge wit h a Np...Np distance 428.4(1) pm. The structure of II contains an infi nite anionic chain [NpO2(C2O4)2]n3n- with isolated Np coordination pol yhedra. The Np-O distances for NpO2+ in I are 184.1(5) and 183.5(5) pm ; in II, 183.2(5) and 183.5(5) pm. Water does not coordinate to Np. Th e similarities and differences in the structures of Np(V) and U(VI) ox alates are discussed.