The electronic spectrum of the confacial bioctahedral complex Cs3Mo2Br9 has been investigated by single-crystal absorption, Zeeman, and MCD spectroscopies. A total of seven distinct band regions were resolved and assigned to transitions essentially within the t(2)(2)t(2)(2) configuration that arises when the pair of t(2z)- orbitals in the t(2)(3)t(2)(3) configuration is decoupled by strong Mo-Mo a bonding. The excited state separations, and in particular the orbital g values, are sensitive to Mo-Mo pi bonding and show clearly that the pi bonding is weaker in the bromide than in the chloride complex.