Oxoselenide triangular molybdenum clusters: Synthesis and characterization of [Mo3SeO3(acac)3(py)3]PF6

► We obtained new cluster complex [Mo3SeO3(acac)3(py)3]PF6. ► The Mo-Mo distance is 2.60 Å. ► The molecular peak from [Mo3SeO3(acac)3(py)3]+ was observed in ESI-MS. ► DFT calculations confirm Mo-Mo bonding in the cluster core. ► Two-electron reduction was detected in cyclic voltammetry.