Synthesis of trans,trans-[MoX2py4][MoX4py2], trans-[MoX2py4]Br3, and structural identification of trans,trans-[MoX2py4][MoX4py2] (X = Cl,Br; py = pyridine)

Trans,trans-MoX₂py₄]MoX₄py₂] (X = Cl, A; Br, B; py = pyridine, C₅H₅N) are the side products of reaction of between (NH₄)₂MoX₅ · H₂O] (X = Cl,Br) with pyridine diluted with methanol. Both trans,trans-MoX₂py₄]MoX₄py₂] are monoclinic, P2₁/n space group, with z = 2 and: a = 12.568(1), b = 9.430(1), c = 14.952(1) Å and β = 100.81(1)° (A); a = 12.551(2), b = 9.533(2), c = 15.366(2) (Å) and β = 99.35(1) (B). Cations and anions are located on the symmetry centers and have eclipsed conformation of the trans located pyridine ligands. Average Mo? X and Mo? N (pyridine) bonds are; (cation) 2.41, 2.21 Å (A); 2.54, 2.21 Å (B); (anion) 2.44, 2.20 Å (A); 2.58, 2.20 Å (B). Anionic part of the compounds can be oxidised by bromine to trans-MoX₄py₂, which precipitates from the solution. Cation can be isolated from the solution in the form of trans-MoX₂py₄]Br₃ (X = Cl, Br). The compounds were also characterised by chemical analysis, infrared spectroscopy and conductivity measurements.