The crystal structure and molecular configuration of the complex dicarbonyl-2,–bipyridinepyridine-π-allylmolybdenum tetrafluoroborate (CO) 2(C 10H 8N 2)(C 5H 5N)(π-C 3H 5)MoBF 4 have been determined from three-dimensional data collected photographically at 22 oC. The unit cell is monoclinic, spacegroup P2 1/ c with four formula units in a cell of dimensions a = 9.702±0.004 Å, b = 13.632±0.001 Å, c = 19.421±0.008 Å, β = 117 o8'±5'. The structure has been refined to R = 0.0815 by the application of an isotropic/anisotropic block-diagonal-approximation least-squares refinement using 2488 independent observed reflections. The ligands form the apices of an approximate octahedron with the molybdenum at its centre. When viewed with the dicarbonyl ligands horizontal, the π-allyl and pyridine ligands lie axially, above and below (respectively) the dicarbonyl plane. The bipyridine plane lies 14.3 o below the horizontal, dipping away from the π-allyl. The other inter-planar angles are π-allyl/dicarbonyl 13.8 o, 2,2–bipyridine/π-allyl 27.7 o. The three allyl carbon atoms are equidistant from the molybdenum atom. The MoC values all lie within ±1.5 σ of the mean value of 2.292±0.009 Å. The inter-carbon angle is 111.4±0.8 o and the CC bond lengths are 1.369±0.013Å and 1.471±0.013 Å. The mean MoC and CO bond lengths are 1.986±0.008 Å and 1.187±0.011 Å respectively and the MoCO angles are near-linear. The bipyridine and pyridine ligands have each been shown to be planar with MoN contacts of 2.250±0.011 Å (Bipy mean) and 2.320±0.007 Å (Py). Some disorder is evident associated with the BF 4 anion. This disorder appeared as distortion of the tetrahedral BF 4 configuration and as high thermal motion of the four fluorine atoms.