Synthesis, crystal structure and selected properties of three new 4-propylanilinium polyoxomolybdates

•Propylanilinum polyoxomolybdates are formed in relatively simple syntheses in different types depending on the reaction conditions.•The layered pentamolybdate phase is the most effective catalyst among the studied compounds.•The thermal stability causes the catalytically active form for the octamolybdate materials (in the studied cyclooctane oxidation reaction) to be the thermal decomposition products of the catalysts, which cannot be properly characterized due to their amorphous character.