Two new members of the oxovanadium-organodiphosphonate system, V-O-R(PO3)(2)(4-), have been synthesized by hydrothermal methods and structurally characterized. The reaction of VCl4, propylenediphosphonic acid, piperazine, and H2O in the mole ratio 1:1.5:3:945 at 200 degrees C and 96 h yields [H2N(C2H4)(2)NH2][(VO)(2)(O3PCH2CH2CH2PO3H)(2)] (1), as green rodlike crystals. The structure consists of ribbons of corner-sharing vanadium square pyramids and phosphorus tetrahedra interconnected by the diphosphonate organic backbone into a stair-step structural motif. The reaction of VCl4, N,N-piperazinebis(methylenephosphonic acid), and H2O in the mole ratio 1:0.8:570 at 125 degrees C for 134 h yields [(VO)(H2O){O3PCH2NH(C2H4)(2)NHCH2PO3}] (2), as light aqua green crystals of cubic habit. The structure of 2 consists of inorganic V/P/O layers linked through the organodiphosphonate backbone into an array of alternating inorganic and organic layers. In contrast to those in 1, the vanadium sites are six-coordinate and the V/P/O layer structure is a defected form of the V-P-O ribbon of 1 with alternate vanadium sites vacant, Compound 1 exhibits magnetic properties consistent with antiferromagnetic coupling of the V(IV) sites, with J/k = -10.3 K as an estimate of the strength of the exchange. Crystal data : C10H26N2O14P4V2 (1), triclinic P (1) over bar, a = 6.244(1) Angstrom, b = 8.687(2) Angstrom, c = 11.156(2) Angstrom, alpha = 88.92(3)degrees, beta = 74.63(3)degrees, gamma = 74.32(3)degrees, V = 560.8(3) Angstrom(3), Z = D-calc = 1,842 g cm(-3), with structure solution and refinement based on 1663 reflections converging at R = 0.0662; C6H12N2O8P2V (2), monoclinic P2(1)/c, a = 7.999(2) Angstrom, b = 8.009(2) Angstrom, c = 9.201(2) Angstrom, beta = 100.24(3)degrees, V = 580.1(3) Angstrom(3), Z = 2, D-calc = 2.021 g cm(-3), 1453 reflections, R = 0.0593.