Two novel piperazinium vanadyl(IV) compounds, (C4H12N2) [VO(C2O4)HAsO4] (1) and (C4H12N2)[VO(C2O4)HPO4] (2), have been prepared under mild hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility. They adopt a one-dimensional structure in which ladder-like chains are constituted by the three-connected V and three-connected X (X = As for 1 and P for 2) centers. Within the infinite chains the oxalate group coordinates to each of the V centers as a bidentate ligand. They are the first inorganic/organic mixed-anion materials prepared in the vanadium arsenate and vanadium phosphate systems. Crystal data for 1: orthorhombic, P2(1)2(1)2(1), a = 6.5595(1) Angstrom, b = 12.4689(1) Angstrom, c = 14.6363(1) Angstrom, Z = 4. Crystal data for 2: as above, except a = 6.4022(4) Angstrom, b = 12.4735(8) Angstrom, c = 14.653(1) Angstrom. According to the results of TG analysis, both compounds are thermally stable to ca. 250 degrees C. Our magnetic study revealed that exchange coupling occurred between the nearest VO2+ centers along the infinite (-V-O-X-O)(2) chains. Good fits of the magnetic susceptibility data were obtained by using the Bonner and Fisher S = 1/2 linear chain model.