Actinide structural studies. Part 7. The crystal and molecular structures of (2,2′-bipyridyl)dinitratodioxo-uranium(VI) and -neptunium(VI), and diacetato-(2,2′-bipyridyl)dioxo-uranium(VI) and -neptunium(VI)

Abstract

The crystal structures of the title compounds, [MO₂(bipy)(NO₃)₂][M = U (1) or Np (2)] and [MO₂(bipy)(CH₃COO)₂][M = U (3) or Np (4)](bipy = 2,2′-bipyridyl) have been determined using X-ray diffraction techniques. Complexes (1) and (2) are isomorphous and isostructural crystallising in the monoclinic system, space group C2/c; (3) and (4) are also isomorphous and isostructural, crystallising in the monoclinic system, space group P2₁/n. All four complexes exhibit hexagonal-bipyramidal co-ordination about the central metal atom. The M–O bond lengths in the MO₂²⁺ cations are 1.763(13)(1), 1.728(7)(2), 1.770(8)(mean)(3), and 1.729(10)Å(mean)(4). The bidentate oxy-anions have M–O distances of 2.472(8)–2.494(13)Å in (1) and (2), and 2.429(9)–2.476(9)Å in (3) and (4). For the bidentate 2,2′-bipyridyl group the M–N distances are 2.578(13)(1), 2.564(9)(2), 2.631 (10) and 2.642(9)(3), and 2.835(13) and 2.842(13)Å(4). This anomalous increase in the M–N distance between complexes (3) and (4) is attributed to overcrowding around the NpO₂²⁺ ion.