Internal rotation around the Mo-Mo bond in Mo2Cl4(PH3)4 is studied by DFT calculations with the B3LYP functional. The lowest singlet (1δ2) and triplet (3δδ*) states are studied, full geometry optimization being performed for each value of the rotational angle (χ). Compared to experimental data and to previous CASSCF calculations, the singlet-triplet energy separation is satisfactorily reproduced provided approximate spin-projected broken-symmetry calculations are used for the singlet state. The geometrical changes due to the internal rotation or the nature of the electronic state are discussed with respect to experimental data. Structural correlations are derived from the geometry optimizations for both singlet and triplet states.
Lledos, A., & Jean, Y. (1998). A density functional study of the internal rotation in the quadruply bonded Mo2Cl4(PH3)4 complex. Chemical Physics Letters, 287(3-4), 243-249. https://doi.org/10.1016/S0009-2614(98)00170-5