Structure of (η-allyl)dicarbonyl(pentane-2,4-dionato)pyridine-molybdenum(II) in the solid and solution states

Abstract

Crystals of the title complex are monoclinic, space group P2₁/c, with a= 6.945(1), b= 24.946(6), c= 9.389 (2)Å, β= 93.71 (1)°, and Z= 4. The structure, solved by the heavy-atom method and refined to R 0.032 for 2 275 independent reflections, contains an Mo(allyl)(CO)₂ unit of approximate C_s symmetry. The molecule as a whole becomes asymmetric when the pseudo-octahedral co-ordination around molybdenum is completed with dionate oxygens and a nitrogen atom which is trans to one of the cis-dicarbonyl ligands. This configuration makes the allyl nuclei non-equivalent as observed in the ¹H and ¹³C n.m.r. spectra at low temperatures. A symmetrical isomer is also detectable at low temperatures, whereas the molecule is fully fluxional at room temperature. The isomer ratio at a particular temperature is dependent on the nature of the solvent.