The Phenomenon of Conglomerate Crystallization. XX-Spontaneous Resolution in Coordination Compounds. XVIII. The Crystallization Behavior and the Crystal and Molecular Structure of Racernic [cis-Co(en)(2)(NO2)(2)](NO2)

The title compound, [cis-Co(en)(2)(NO2)(2)](NO2) (1), crystallizes in the polar, nonenantiomorphic, monoclinic space group, Cc, with lattice constants: a = 9.198(2) angstrom, b = 12.444(2), c = 9.963(3), and beta = 96.76(2)degrees V = 1132.39 angstrom(3) and d(calc; Z = 4) = 1.860 g cm(-3). Thus, with NO2- as the counteranion, [cis-Oo(en)(2)(NO2)(2)] crystallizes in a heterochiral lattice containing racemic pairs of cations, A total of 2699 data were collected over the range of 4 degrees <= 20 <= 70 degrees of these, 1859 (independent and with l >= 3 sigma (l)) were used in the structural analysis. Data were corrected for absorption (mu = 15.465 cm(-1)) and the relative transmission coefficients ranged from 0.9934 to 0.7112. Refinement was carried out for both lattice polarities and the final R(F) and R-w(F) residuals were, respectively, 0.0242 and 0.0202 for (-) and 0.0264 and 0.0243 for (+++). Thus, the former was selected as correct for our specimen. Unlike all previous X-ray diffraction studies of the structural properties of the cation [cisCo(en)(2)(NO2)(2)](+), which are found to have a pair of oppositely configured en rings [i.e., Delta(lambda delta) or Lambda(delta lambda)], we find that in 1 the cations are in the lowest energy conformation and configuration; i.e., Delta(lambda lambda) or Lambda(delta delta). We attribute this change in configuration to the formation of strong interionic hydrogen bonds between nitrite anion oxygens and the axial-NH2 hydrogens, which markedly weaken the intermolecular and intramolecular hydrogen bonds between ligand-NO2 oxygens and the hydrogens of those same amine moieties. Thus, the nitrite anions behave exactly as nitrate anions, except that the hydrogen bonds found here are stronger than those formed by the latter. This is as expected since the negative charge