The quadruply bonded dimolybdenum complexes with alkyl-substituted pyridines of the formula Mo2Cl4(R-py)(4) (R-py = 4-pic (4-methylpyridine) (1), 3,5-lut (3,5-dimethylpyridine) (2), and 4-Bu-t-py (4-tert-butylpyridine) (3)) have been prepared. Nine different compounds, in which there are 11 independent molecules, have been obtained in crystalline form, and their crystal structures have been investigated by X-ray diffraction, Three types of geometric isomers which differ by the angle of internal rotation about the Mo-Mo axis have been recognized in these structures. The eclipsed structures 1-3a display pyridine ligands opposite to each other across the metal-metal bond and have a virtual symmetry D-2h The noncentrosymmetric D-2d structures 1-3b have each pyridine ligand opposite to a Cl atom. The molecules 3c-f have a partially staggered D-2 geometry with N-Mo-Mo-N torsion angles ranging from 10.4 degrees to 25.2 degrees. As a result of this work it is now clear that Mo2Cl4(R-py)(4) compounds do not show a preference for D-2h conformation rather than D-2d conformation. In fact, they seem unusually unrestricted in their rotational conformation, and packing forces appear to have a major influence on the conformation adopted. Further clarification of this question will require spectroscopic study of solutions.