2 NEW MIXED-VALENCE IRON PHOSPHATES TEMPLATED BY PIPERAZINE - (C4H12N2)[FE-4(OH)(2)(HPO4)(5)] AND (C4H11N2)(0.5)[FE-3(HPO4)(2)(PO4)(H2O)]

Two piperazine-templated iron phosphates, (C4H12N2)[Fe-4(OH)(2)(HPO4)( 5)] (1) and (C4H11N2)(0.5)[Fe-3(HPO4)(2)(PO4)(H2O)] (2), have been syn thesized under solvothermal conditions and characterized by single-cry stal X-ray diffraction, Mossbauer spectroscopy, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic space group C2/m ( no. 12) with a = 25.706(3), b = 6.4492(6), c = 6.3790(6) Angstrom, bet a = 102.601(2)degrees, V = 1032.0(3) Angstrom(3) and Z = 2. The 3-D fr amework structure consists of layers of iron phosphate which are pilla red through HPO4 groups to generate intersecting 8-ring channels with piperazinium dications at the intersections of these channels. Each la yer contains infinite chains of edge-sharing (FeO6)-O-II octahedra whi ch are connected to each other via corner-sharing (FeO6)-O-III octahed ra and HPO4 groups. Compound 2 crystallizes in the monoclinic space gr oup C2/c (no. 15) with a = 30.8924(4), b = 6.3733(1), c = 12.5552(2) A ngstrom, beta = 101.946(1)degrees, V = 2418.41(7) Angstrom(3), and Z = 8. The compound has a layered structure with piperazinium monocations in the interlayer space. Each layer consists of a dimer of edge-shari ng octahedra with the composition (FeFeO10)-Fe-II-O-III which shares e dges with four (FeO5)-O-II trigonal bipyramids to form a hexamer as th e building unit. Each such hexamer is connected to others by corner sh aring and through phosphate groups. Both compounds are mixed-valence a s indicated from bond valence calculations, Mossbauer measurements, an d electric field gradient calculations.