Sulfate-doped VOHPO4 . 0.5H(2)O precursors with molar ratios of 0 < S:V < 0.1 were prepared by three different methods and calcined to the respective sulfate-doped (VO)(2)P2O7 catalysts in which the distances of the crystal planes parallel to (200) are enlarged. Sulfate doping influences both the crystal structure and the selectivity to maleic anhydride in the oxidation of n-butane. The best catalytic selectivity was achieved for slightly disordered catalysts and moderate lattice distances.