Heterobimetallic Chromium Manganese Carbonyl Nitrosyls: Comparison with Isoelectronic Homometallic Binuclear Chromium Carbonyl Nitrosyls and Manganese Carbonyls

The heterometallic chromium-manganese carbonyl nitrosyls CrMn(NO)(CO)n (n = 9, 8) have been investigated by density functional theory. The lowest energy CrMn(NO)(CO)9 structures have unbridged staggered conformations with a ~2.99 Å Cr–Mn single bond similar to the experimental and lowest energy structures of the isoelectronic Mn2(CO)10 and Cr2(NO)2(CO)8. A significantly higher energy CrMn(NO)(CO)9 isomer has a nearly symmetrical bridging nitrosyl group and a very weakly semibridging carbonyl group. The two lowest energy structures of the unsaturated CrMn(NO)(CO)8 have a five-electron donor bridging η2-µ-NO nitrosyl group or a four-electron donor bridging η2-µ-CO group, as well as a Cr–Mn single bond of length ~2.94 Å. The next higher energy CrMn(NO)(CO)8 structure has exclusively terminal CO and NO ligands and a shorter Cr–Mn single bond of ~2.85 Å, suggesting an 18-electron configuration for the manganese atom and a 16-electron configuration for the chromium atom indicated by a vacant coordination site nearly perpendicular to the Cr–Mn bond.

A complex with nitrogen single, double, and triple bonds to the same chromium atom: synthesis, structure, and reactivity

A complex with single, double and triple bonds between nitrogen and the same metal center has been synthesized, [NCr(NPh)(NPri2)2]−. The complex shows differential activity, with some electrophiles attacking the imido and others the nitrido.

Modulation functions of incommensurately modulated Cr2P2O7 studied by the maximum entropy method (MEM)

The maximum entropy method (MEM) has been used to determine electron density in superspace of incommensurately modulated chromium pyrophosphate from X-ray diffraction data measured by Palatinus et al. [(2006), Acta Cryst. B62, 556–566]. Chromium pyrophosphate, Cr2P2O7, contains ordered regions (83% of the volume) and regions with disorder. Analysis of the MEM density has allowed the determination of the displacive modulation functions within ordered regions. The disordered regions can be described as the alternate occupation of two conformations of the pyrophosphate group and two positions of the chromium atom, with occupational probabilities that depend continuously on the phase of modulation t. A structure model based on the interpretation of the MEM density provides a fit to the diffraction data of the same quality as the model given by Palatinus et al. (2006). The failure to find a model that better fits the data is attributed to the intrinsic inaccuracy of ∼ 0.01 Å for positions derived from the MEM and to the difficulties in constructing an appropriate model for the anharmonic ADPs and their modulation functions from electron densities.

Kristallstruktur und Eigenschaften von Chrom(II)-Tetrachloroaluminat/Crystal Structure and Properties of Chromium(II)-Tetrachloroaluminate

Chromium(II)tetrachloroaluminate can be prepared by reaction of chromium, chromium trichloride and aluminum trichloride in the molar ratio 1 : 1.94 : 5.79 or by reaction of stoichiometric amounts of chromium dichloride and aluminum trichloride. Sublimation of the compound yields phase-pure samples of colourless crystals. Cr(AlCl4)2 crystallizes in the non-centrosymmetric orthorhombic space group Pca21 (No. 29), a = 1511.38(3), b = 604.71(1), c = 1301.76(3) pm. The aggregation of Cr(AlCl4)2 molecules leads to a square-bipyramidal coordination of the chromium atom typical of high-spin d4 ions due to the Jahn-Teller effect. The relationship to centrosymmetric Pd(AlCl4)2 (P21/c) which is built up of similar molecules was established by means of a group-subgroup symmetry tree. The temperature dependence of the magnetic susceptibility agrees with Curie-Weiss behaviour (μeff = 4.70 μB,Θ = −1.3 K).