A tungsten chloromethoxide was prepared by the methanolysis of WCl6. The resulting solutions were modified by addition of acetylacetone to improve their stability. The resulting deep blue solutions were studied by infrared and Raman spectroscopy. The structure of the solutions was characterized by polynuclear tungsten species containing WOW bonds. The solutions were used for preparing thin films, by spin-coating onto oxidized silicon substrates, and powders, by evaporation at reduced pressure. The as-dried thin films and powders were heat-treated at various temperatures up to 700 °C and characterized by infrared and Raman spectroscopy and X-ray diffraction. The investigations showed that the precursor structure follows a continuous evolution to the final WO3 structure, by further condensation and thermally activated reorganization of the initial species. The final crystalline structure was a mixture of …