New bis (en e-1,2-dithi ol ato)-oxido-al coholato molybdenum(VI) and-oxido-thiolato molybdenum(VI) anionic complexes, denoted as [(MoO)-O-IV(ER)L-2](-) (E = O, S; L = dimethoxycarboxylate-1,2-ethylenedithiolate), were obtained from the reaction of the corresponding dioxidomolybdenum(VI) precursor complex with either an alcohol or a thiol in the presence of an organic acid (e.g., 10-camphorsulfonic acid) at low temperature. The [(MoO)-O-VI(ER)-L-2](-) complexes were isolated and characterized, and the structure of [(MoO)-O-VI(OEt)L-2](-) was determined by X-ray crystallography. The Mo(VI) center in [(MoO)-O-VI(OEt)L-2](-) exhibits a distorted octahedral geometry with the two ene-1,2-dithiolate ligands being symmetry inequivalent. The computed structure of [(MoO)-O-VI(SR)L-2](-) is essentially identical to that of [(MoO)-O-VI(OR)L-2](-). The electronic structures of the resulting molybdenum(VI) complexes were evaluated using electronic absorption spectroscopy and bonding calculations. The nature of the distorted O-h geometry in these [(MoO)-O-VI(EEt)L-2](-) complexes results in a lowest unoccupied molecular orbital wave function that possesses strong Ir* interactions between the Mo(d(xy)) orbital and the cis S(p(z)) orbital localized on one sulfur donor from a single ene-1,2dithiolate ligand. The presence of a covalent Mo-S-dithioiene bonding interaction in these monooxido Mo(VI) compounds contributes to their low-energy ligand-to-metal charge transfer transitions. A second important d-p pi bonding interaction derives from the similar to 180 degrees O-oxo-Mo-E-C dihedral angle involving the alcoholate and thiolate donors, and this contributes to ancillary ligand contributions to the electronic structure of these species. The formation of [(MoO)-O-VI(OEt)L-2](-) and [(MoO)-O-VI(SEt)L-2](-) from the dioxidomolybdenum(VI) precursor may be regarded as a model for the active-site formation process that occurs in the dimethyl sulfoxide reductase family of pyranopterin molybdenum enzymes.