The crystal structure of hexamminecobalt(III) hexacyanocobaltate(III): an accurate determination

Abstract

The crystal structure of [Co(NH3)6] [Co(CN)6] has been determined by three-dimensional X-ray data in an attempt to study the charge distribution in complexes. The crystals conform to the space group R3 with one formula unit in a cell of dimensions a, = 7"255(3) A and e, = 97.65(2) ° at 25.5 °C. Intensity data were collected with Mo Ke radiation up to sin 0/2 = 1.3 ,~,-~ on an automated four-circle diffractometer. Positional and anisotropic thermal parameters for all atoms were refined by full-matrix least-squares methods. A correction for anisotropic extinction effects was included in the least-squares refinement. The conventional R index is 0.028 for 2205 independent reflexions. The complex ions are packed in much the same way as the ions in caesium chloride. Both complex ions possess the rigorous crystallographic symmetry 3. The coordination around the metal atoms is remarkably regular octahedral. The Co-N distance is 1.972(1) A and Co-C is 1.894(1) ,~,; the angles NCoN and CCoC are 89.78(5) and 90.25(6) °, respectively. The C-N distance is 1.157(2) A. The direct integration of the electron density around the central cobalt atom within a sphere of radius 1.22/~ showed that each metal atom has largely neutralized resultant charges: [Co(NH3)6] 3+, 26.3 + 0"3 e and [Co(CN)6] 3-, 26-8 + 0"3 e.

Theoretical and experimental (113 K) electron-density study of lithium bis(tetramethylammonium) hexanitrocobaltate(III)

“…4(a). The features of the Laplacian distribution around the Co atom closely resemble those found in the deformation maps for [Co(NH3) (Iwata & Saito, 1973) and KzNa[Co(NOz) 6] (Ohba et al, 1978). In Fig.…”

Theoretical calculations of deformation densities in some transition metal complexes

“…Further investigations are required to test this hypothesis. The peaks in this theoretical study are located at shorter distances from the metal atoms and are higher than those found in analogous experimental investigations (Rees & Coppens, 1973;Iwata & Saito, 1973;Marumo et al, 1974). The main reason for this discrepancy is probably the inadequate description of the thermal motion.…”

“…From the deformation, or residual, density (defined here as the difference between the electron density distribution in a molecular system and the corresponding density obtained from a superposition of the constituent spherically averaged atoms) a-bonds, ~-bonds, bent-bonds, lone-pair electrons and the like may be recognized. Some recent investigations (Rees & Coppens, 1973;Iwata & Saito, 1973;Marumo, Isobe, Saito, Yagi & Akimoto, 1974) have also demonstrated deformation density features in the vicinity of transition metal atoms. These departures from sphericity are probably very common and should be observable from the results of many crystal structure determinations.…”

Electron-density distribution in rutile crystals

“…There is no indication that the charge densities of Ti 4+ (having no d electrons) are deformed in an octahedral crystal field. This result seems to support our conclusion that the aspherical charge densities of Ni 2+ (3d 8) in 7-Ni2SiO4 are due to d electrons placed in an octahedral crystal field.An indication of 3d electrons in the t2g orbitals of Ni 2 ÷ and Co 3÷ was observed in the final difference syntheses of 7-Ni2SiO4 and [Co(NHa)6][Co(CN)6] (Marumo, Isobe, Saito, Yagi & Akimoto, 1974;Iwata & Saito, 1973). In the difference maps eight small peaks were arranged at the corners of a cube around the transition metal atom, the peaks being at 0.45 A from the metal atom.…”