Mixed μ-phosphido or μ-thiolato μ-halo-dimolybdenum(III) compounds [Mo2Cp2(μ-SMe)2(μ-X)(μ-Y)] (X = PPh2, Y = Cl (1); X = SCH3, Y = Br (3), I(4)) have been studied. Syntheses and X-ray structures of the new bromo and iodo analogues of [Mo2Cp2(μ-SMe)3(μ-Cl)] (2) are reported. While preparing 3 a side-product 5 was obtained and structurally characterised as the Mo5 system [{Mo2Cp2Br(μ-O)(μ-SMe)2}2(μ-MoO4)], containing a {MoIV–MoIV–O–(MoVIO2)–O–MoIV–MoIV} unit. The influence of the bridging groups on the structures and electrochemical behaviour of the complexes [Mo2Cp2(μ-SMe)2(μ-X)(μ-Y)] 1–4 has been investigated. In MeCN–[NBu4][PF6] the first oxidation of [Mo2Cp2(μ-SMe)2(μ-PPh2)(μ-Cl)] (1) is quasi-reversible, contrasting with the essentially irreversible first oxidation of the thiolate analogue [Mo2Cp2(μ-SMe)3(μ-Cl)] (2) under similar conditions. The effects of lowering the temperature or increasing the scan rate on the oxidation of 1 were examined: the initial quasi-reversible oxidation at first became irreversible but at still higher scan rates or lower temperatures the oxidation was again quasi-reversible. This suggests that the oxidation of 1 in MeCN is followed by reversible coordination of acetonitrile to afford the species [Mo2Cp2(μ-SMe)2(μ-PPh2)(Cl)(MeCN)]+ (7+). Cyclic voltammetry of [Mo2Cp2(μ-SMe)3(μ-Y)](Y = Br (3) or I (4)) showed two quasi-reversible diffusion-controlled oxidation steps in CH2Cl2–[NBu4][PF6] or thf–[NBu4][PF6]. In acetonitrile, the fast loss of the halide ligands results in the formation of [Mo2Cp2(μ-SMe)3(MeCN)2]+ species.