The Phenomenon of Conglomerate Crystallization. V. Clavic Dissymmetry in Coordination Compounds. IV. A Neutron Diffraction Study of K[ trans-Co(NH 3) 2(NO 2) 4

Abstract

The structure of K[ trans-Co(NH 3) 2(NO 2) 4] has been determined by neutron diffraction data collected at room temperature ( ca. 21 °C). The substance crystallizes as a conglomerate of antipodal crystals, many large enough for neutron diffraction work. The space group and cell constants are: P2 12 12 1; a = 11.275(3), b = 12.806(5) and c = 6.696(3) Å. The cell volume is 966.82 Å 3 and given the M r of 316.12 g mol −1, the D(calc; Z = 4) is 2.170 g cm −3. The data (1553 unique reflections) were corrected for absorption (μ = 79.533 cm −1) and there was no decay during data collection, as expected from the X-ray study. All heavy atoms were initially placed at the positions found with X-rays, refined isotropically and, after locating the hydrogens in a difference map, all atoms were refined isotropically. Conversion to anisotropic motion was followed by 12 cycles of least-squares fitting (200 variables), at which point the structural refinement converged to its final R and R w factors of 0.056 and 0.056, respectively. The goodness of fit was 1.133. The positional parameters of the two studies are in close agreement, as expected. For example, the average value of the CoN(NH 3) bonds in the X-ray and neutron studies are, respectively, 1.958(3) Å and 1.949(9) Å. The average value of the CoN(NO 2) distances for the X-ray and neutron studies are 1.956(3) Å and 1.948(9) Å, while the average NO distances are 1.230(4) and 1.222(6) Å for the former and latter, respectively. The most important result derived from this study is the accurate location of the hydrogens of the −NH3 ligands which had caused problems in two previous X-ray studies of salts of this anion. In this analysis, we found that −N1(NH 3) is well behaved thermally while −N2(NH 3) is much less so, the reason being that the three hydrogens of the amines attempt to form hydrogen bonds with the adjacent oxygens of the basal plane −NO 2 ligands — which is impossible while satisfying all of them equally well. One of the two amino ligands manages better than the other one, as we shall demonstrate below.