Cr CO Bond Research Articles

The molecular structures of pyridine-chromiumpentacarbonyl and bis(pyridine)-chromiumtetracarbonyl

The structures of pyridinechromiumpentacarbonyl, (1), and bis(pyridine)chromiumtetracarbonyl,(2) have been determined. (1) crystallizes in the space group Pbam with a = 15.289(3) Å, b = 19.276(5) Å and c = 7.677(6) Å. (2) crystallizes in the space group P 1 with a = 7.365(2) Å, b = 8.136(2) Å, c = 13.491(4) Å, α = 89.49(2)°, β = 88.89(2)°, and γ = 63.09(2)°. The structures refined to R w values of 0.020 and 0.034 for (1) and (2), respectively. In both cases the pyridine rings are planar and stagger the cis CrCO bonds. A comparison of the structural results from these two compounds to piperidinechromiumpentacarbonyl and Cr(CO) 6 seems to indicate that the pyridine ligand is a weaker σ-donor and stronger π-acceptor than the saturated analog, piperidine.

On internal rotation in gaseous benzenechromium tricarbonyl

The vapor phase molecular structure of benzenechromium tricarbonyl, C 6H 6Cr(CO) 3, has been studied by electron diffraction. On the basis of the diffraction data and of auxiliary vibrational calculations, it is concluded that in the vapor phase the molecule is a nearly unhindered internal rotor. Its vapors consist of a mixture of several conformations which differ by the rotational arrangement of the six-ring with respect to the carbonyl groups, whereas solid state studies showed the molecule to be in the pure staggered form. The CC bond distance of the six-ring ( r a ) was found to be 1.417 ± 0.003 Å and slightly longer than in free benzene (1.397 Å). The OCCrCO bond angle was found to be 88.6 ± 1.1° indicating a semi-octahedral arrangement; r a(CrC(CO)) = 1.863 ± 0.005 Å and r a(CrC(C 6H 6)) = 2.208 ± 0.006 Å.

The crystal structure of trimethylenemethanechromium tricarbonyltriphenylphosphine

Abstract The crystal structure of trimethylenemethanechromium tricarbonyltriphenylphosphine has been determined by conventional Patterson and Fourier methods. The structural results of a full matrix least squares refinement (R1 = 0.083, R2 = 0.089) and those of a block-diagonal least squares refinement (R1 = 0.088, R2 = 0.087) are not significantly different by Cruickshank's test. The compound crystallizes in the monoclinic space group C2/c with 16 molecules in a unit cell of dimensions a = 36.955(3), b = 10.789(1), c = 22799(3) », β = 100.80(1)°. The experimental and calculated densities are 1.36 g/cm3 and 1.35 g/cm3, respectively. Carboncarbon bond distances within the trimethylenemethane ligand, as well as metalligand π-bonding distances, are equivalent with a mean value of 1.42(1) » for the former and 2.23(1) » for the latter. The trimethylenemethane moiety is quite non-planar with the central atom displaced 0.28 » from the plane of the other three carbon atoms. The structure is compared to several previously-reported iron complexes which have trimethylenemethane type ligands. The CrCO bond trans to the triphenylphosphine is short [mean = 1.83(1) » ] compared with the other two [mean = 1.86(1), 1.87(1) » ] in the structure. This is discussed in terms of a trans influence. The effects of the σ and π donor or acceptor properties of various ligands upon the metalCO bond lengths and CO stretching frequencies in numerous metal complexes ad discussed.