Solid state coordination chemistry of the oxovanadium-diphosphonate system: Structural consequences of aryl tethers on materials of the type cation/V _xO_y/diphos, where cation = organoammonium and diphos = 1,4-phenyldiphosphonic acid

Hydrothermal reactions of V₂O₅, 1,4- phenyldiphosphonic acid and an appropriate organoamine, in the presence of HF as solubilizer, were exploited to prepare a series of materials of the general type [organoammonium cation]_n[V_xO_y(H _mO₃PC₆H₄PO₃H _p)₃]. Compound 1, [H₃N(CH₂) ₄NH₃][V₂O₄(O₃PC ₆H₄PO₃)], exhibits a one-dimensional V-P-O substructure, linked through the phenyl tethers of the ligand into a {V2O4(O3PC6H4PO3)}n2n- layer. Compound 1 is a unique example of a V(V)-diphosphonate phase. Compounds 2 and 3, [H₃N(CH ₂)₂NH₃][V₂O₂(O ₃PC₆H₄PO₃H)₂] and [H ₂pip][V₂O₂(O₃PC₆H ₄PO₃H)₂] (H₂pip = piperazinium), exhibit identical two dimensional {V2O2(O3PC6H4PO3H)2}n2n- substructures, constructed from {V2O2(O3PR)2(HO3PR)2}n2n- ribbons connected through the phenyl tethers of the ligands. The three-dimensional framework of [H ₃N(CH₂)₇NH₃]₂[V ₃O₄(O₃PC₆H₄PO ₃)₂] (4) consists of V-P-O layers characterized by trinuclear V(IV)-oxide subunits and 9 and 12 polyhedral connect rings; the layers are buttressed by the phenyl spacers to provide the typical "pillared" layer structure common to metal diphosphonate materials. Compound 5, [H₂dabco][V₂F₃O₂(O ₃PC₆H₄PO₃H)]·H₂O, is also three-dimensional with oxyfluoro-vanadium(IV) chains linked through the diphosphonate ligands into a framework structure with void spacers to accommodate the {H₂dabco}²⁺ cations (dabco = diamino bicyclo octane). The magnetic properties of 2-5 reflect the structural characteristics of the materials.