Hydrothermal Syntheses and Crystal Structures of Two Oxovanadium - Organodiphosphonate Phases: [H₂N(C₂H₄)₂NH₂][(VO)₂(O₃PCH₂CH₂CH₂PO₃H)₂], a “Stair-Step” Structure Incorporating an Organic Cationic Template, and [(VO)(H₂O){O₃PCH₂NH(C₂H₄)₂NHCH₂PO₃}], a Layered Structure “Pillared” by a Piperazinium-Tethered Diphosphonate

Two new members of the oxovanadium-organodiphosphonate system, V-O-R(PO₃)₂⁴⁻, 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 °C and 96 h yields [H₂N(C₂H₄)₂NH₂][(VO)₂(O₃PCH_2- CH₂CH₂PO₃H)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 °C for 134 h yields [(VO)(H₂O){O₃PCH₂NH(C₂H₄)₂NHCH₂PO₃}] (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) sites₂ with J/k = −10.3 K as an estimate of the strength of the exchange. Crystal data: C₁₀H₂₆N₂O₁₄P₄V₂ (1), triclinic P1, a = 6.244(1) Å, b = 8.687(2) Å, c = 11.156(2) Å, a = 88.92(3)°, ß = 74.63(3)°, ? = 74.32(3)°, V = 560.8(3) ų, Z = 1, D_calc = 1.842 g cm⁻³, with structure solution and refinement based on 1663 reflections converging at R = 0.0662; C₆H₁₂N₂O₈P₂V (2), monoclinic P2₁/c, a = 7.999(2) Å, b = 8.009(2) Å, c = 9.201(2) Å, ß= 100.24(3)°, V = 580.1(3) ų, Z = 2, D_calc = 2.021 g cm⁻³, 1453 reflections, R = 0.0593.