This invention relates to precursors of the molybdenum-containing materials such as molybdenum trioxide MoO3. These precursors can be used to prepare polymetallic oxides materials varying metals proportions or they can be used for composite phases as well. Moreover, these precursors are highly soluble in polar solvents as the water or alcohols. It follows their potential to also obtain materials containing molybdenum as thin films. These precursors are obtained by solid state reaction of polycarboxylic acids and ammonium molybdate (NH4)6Mo7O24.4H2O.