Analogies and differences between compounds of molybdenum and other early transition metals (Ti, V, Nb, Ta, W)

The existence of several isomers of the ions (MoO2F2(AB)) could be envisaged. The fact that there is only one form can be explained by the influence of π-bonding. One finds this effect in about 15 new ions (MOnFm(AB))− (n = 0, 1, 2, n + m = 4, AB = bidentate ligand; M = Mo, W, Ti, V). The trans position has also been observed in monomeric or dimeric compounds (e.g., (Mo2O4F4(C2O4))2−). Although previous workers have reported the reduction of molybdenum(VI) in HBr medium, by reducing the rate of the oxidation-reduction process, we have been able to observe the co-existence of Br− and Mo(VI) ions when preparing numerous compounds with a view to exchange. The natural preferential selection of structural forms is found through exchanging F, Cl, Br. X-ray crystallographic measurements allow one to observe the resemblance between the ligands O, F, Cl, OO, which makes it possible to broaden the idea of oxo-species as defined by Selbin and Mitchell. These analogies are not apparent from spectroscopic methods.