Actinide structural studies. Part 1. Crystal and molecular structures of dinitratodioxobis(triphenylphosphine oxide)neptunium(VI), dinitratodioxobis(triphenylphosphine oxide)uranium(VI), and dichlorodioxo-(triphenylphosphine oxide)neptunium(VI)

Abstract

The crystal structures of the title complexes, [NpO2(OPPh3)2(NO3)2](1), [UO2(OPPh3)2(NO3)2](2), and [NpO2(OPPh3)2Cl2](3), have been determined using X-ray diffraction methods. Compounds (1) and (2) are isomorphous and isostructural. Their crystals are monoclinic, space group P21/c, with hexagonal-bipyramidal co-ordination about the heavy atoms. The bidentate nitrate groups are trans to each other and bonded to the metal (M–O 2.52–2.54 Å), as are the triphenylphosphine oxide ligands (M–O 2.35–2.36 Å). The M–O bond lengths in the MO22+ cations (M = Np or U) are 1.739(10) and 1.764(9)Å respectively. Compound (3) is monoclinic, space group P21, and exhibits distorted octahedral co-ordination about neptunium, the trans ligands having Np–Cl lengths of 2.622(14) and 2.645(13)Å; for the triphenylphosphine oxide groups, Np–O lengths are 2.261(19) and 2.288(15)Å. The NpO22+ cation has Np–O bond lengths of 1.721(16) and 1.751(18)Å. Lattice parameters are: for (1)a= 11.038(5), b= 18.838(7), c= 10.897(4)Å, β= 128.27(3)°, and z= 2; for (2), a= 11.043(1), b= 18.880(3), c= 10.870(2)Å, β= 128.17(1)°, and Z= 2; for (3), a= 10.757(4), b= 18.716(4), c= 10.734(3)Å, β= 124.05(2)°, and Z= 2. The structures have been refined to R values of 0.049 (1), 0.028 (2), and 0.042 (3) using respectively, 2 821, 2 638, and 2 063 observed diffractometer-measured intensities.