| Popis: |
The crystal structure of ammonium oxobisoxalatobisaquoniobate(V) trihydrate NH 4 [NbO(C 2 O 4 ) 2 (H 2 O) 2 ] · 3H 2 O has been determined from three-dimensional X-ray data and re-investigated by neutron diffraction, to obtain information concerning the correct formulation of the compound and the hydrogen-bond system. The crystals are monoclinic, space group P2 1 n , with a = 12.308(3), b = 16.368(3), c = 6.578(2) A , β = 92.63(2)° and Z = 4. All atoms were refined with anisotropic thermal parameters. The structure consists of a three-dimensional packing of ammonium cations and complex anions, described by the formula [NbO(C 2 O 4 ) 2 (H 2 O) 2 ] − and crystalline-water molecules. The niobium atom has a pentagonal bipyramidal environment. The shortest and the longest niobium-oxygen bond distances (Nb = O and Nb-OH 2 at 1.706(6) and 2.299(6) A, respectively) are axial and nearly perpendicular to the pentagonal equatorial plane, which consists of four oxygen atoms from two oxalato groups and one water molecule (with the niobium-oxygen distances in the range 2.105–2.135 A). Bond lengths, especially of hydrogen atoms, together with IR spectra are discussed in terms of the structure refined by neutron data. |
