The reaction of [Mo(S2)(S2CNEt2)3] (1) with 1 equiv of meta-chloroperbenzoic acid (mCPBA) in CH2Cl2 at 0-degrees-C yields [Mo(S2O)(S2CNEt2)3] (2) in approximately 70% yield. Complex 2 crystallizes from MeNO2/Et2O as the hemiether solvate in the monoclinic space group C2/c with the following unit cell dimensions at -165-degrees-C : a = 18.294(4) angstrom, b = 9.468(2) angstrom, c = 32.101(7) angstrom, beta = 92.75(1)-degrees, and Z = 8. A total of 2641 unique data with F > 2.33sigma(F) were refined to values of R and R(W) of 3.99 and 3.89%, respectively. The structure of 2.1/2EtO shows a distorted pentagonal bipyramidal Mo center, with the S2O ligand coordinated to an axial site in an asymmetric eta2-S,S’-fashion. The EPR and electronic spectra and electrochemical properties of 1 and 2 are very similar : for 1, [g] = 1.977, [A(Mo-95,Mo-97)] = 38 G, and E1/2 = -0.23 and -1.44 V vs Fc/Fc+ in CH2Cl2/0.5 M Bu4nNPF6; for 2, [g] = 1.982, [A] = 39 G, and E1/2 = -0.04 and -1.62 V. All the aforementioned electrochemical processes are quasi-reversible at 25-degrees-C, bulk controlled potential electrolyses affording mixtures of products in all cases. Ferrocenium oxidation of 1 in the presence or absence of H2O affords salts containing the known ions [MoO(S2CNEt2)3]+ and [Mo(S2CNEt2)4]+, respectively. Extended Huckel MO calculations show that S2O is both a weaker pi-acid and pi-base than S2 in this system and that the electronic structures of 1 and 2 are similar, in agreement with experimental observation, leading to the conclusion that 2 is best considered as a Mo(V) complex bearing an (S2O)2- ligand.