The crystal structure of deuterated trans-Tetraamminedinitronickel(II) at 4.2 K by neutron diffraction

Abstract

The crystal structure of deuterated trans-tetraamminedinitronickel(II), Ni(ND₃)₄(NO₂)₂, has been determined by single-crystal neutron diffraction methods at 4·2 K. Crystals are monoclinic, C2/m, a 1058(l), b 672(1), c 586.3(3) pm, β 114.82(5)º, Z = 2. Diffractometry has provided Bragg intensities for 219 independent reflections; and the structure has been refined by full-matrix least-squares methods to R(F²) 0·070 and χ² 3·8. There are slight differences in the molecular geometries determined by neutron diffraction and earlier X-ray determinations of Ni(NH₃)₄(NO₂)₂ at 295 and 130 K. Small, but significant, decreases are evident in all non-hydrogen bond lengths on decrease in temperature from 295 to 4·2 K, up to a maximum of 2·0(4) pm for the Ni-NH₃/ND₃ bond. The magnitudes of these decreases are correlated with the force constants of the bonds. The intermolecular geometry and thermal parameters show that in the ab plane there is a network of relatively strong, linear N-D···O hydrogen bonds. In the c* direction there is a slightly bent, longer, N-D(1)···O bond which is weaker. This causes a large amplitude of rigid-body translational motion in the c* direction, together with high thermal motion of D(1) in the b axial direction.