Two cis-dioxomolybdenum(VI) complexes [MoO2L] (L: L 1, 2 and L: L 2, 3) in a phenol-based sterically encumbered N2O2 ligand environment have been synthesized, and their crystallographic characterizations are reported. The orange crystals of 2 are monoclinic, space group P21/a with unit cell dimensions as a=16.2407(17) Å, b=7.2857(8) Å, c=18.400(2) Å, β=98.002(9)°, Z=4, and d cal=1.486 g cm-3. The light orange crystals of 3, however, are orthorhombic, space group, Pbcn, with unit cell dimensions a=8.3110(12) Å, b=12.637(3) Å, c=34.673(5) Å, Z=4, and d cal=1.187 g cm-3. The structures were refined by a full-matrix least-squares procedure on F 2 to a final R=0.046 (0.055 for 3) using 4944 (3677) all independent data. In both the cases, the Mo atom exists in a distorted octahedral geometry defined by a N 2O4 donor set, which features a cis-Mo(-O)2 and a trans-Mo(OPh)2 arrangement. Compound 2 undergoes a quasireversible one-electron reduction at -1.3 V vs Ag/AgCl reference due to Mo VIO2/MoVO2 electron transfer and thus providing a rare example of steric solution to the comproportionation- dimerization problem encountered frequently in the development of valid biomimetic models for the active sites of oxomolybdenum enzymes. © 2006 Springer Science+Business Media, Inc.