trans-[W(O)(F)(dppe)(2)](BF4) (dppe = Ph2PCH2CH2PPh2, 1,2-bis(diphenylphosphino)ethane) (10) has been synthesized. From this, the neutral trans-[W(O)(2)(dppe)(2)]. 2CH(3)OH (11) was prepared by a hydrolysis and deprotonation reaction with Et4NOH in methanol/water. Together with the analogous molybdenum compound (2) this compound afforded by substitution under acid conditions salts of trans-[M(O)(X)(dppe)(2)](+) ions (M = Mo, W; X = OH, OCH3, Cl, Br, I, NCS) and trans-[Mo(O)(N-3)(dppe)(2)](CF3SO3) (9). All the compounds have low-spin d(2) electronic configuration. The compounds were characterized by P-31{H-1} NMR, positive FAB-ionization mass spectrometry, UV-vis spectroscopy, and vibrational spectroscopy. X-ray crystallographic studies were carried out on compounds 10, 11, trans-[W(O)(OH)(dppe)(2)](ClO4) (12), and trans-[W(O)(NCS)(dppe)(2)](BPh4) (16). The electronic spectra of the mono-ore species are consistent with the lowest energy transitions being of d(xy) --> {d(zx), d(yz)} character. No ligand-field transitions are observed for the dioxo tungsten complex. Identical pi-spectrochemical series were found for the two metals. The shielding of the phosphorus nuclei determined by P-31{H-1} NMR is significantly influenced by the nature of the axial ligands.