Two New Mixed-Valence Iron Phosphates Templated by Piperazine: (C 4 H 12 N 2 )[Fe 4 (OH) 2 (HPO 4 ) 5 ] and (C 4 H 11 N 2 ) 0.5 [Fe 3 (HPO 4 ) 2 (PO 4 )(H 2 O)]
1998; American Chemical Society; Volume: 10; Issue: 7 Linguagem: Inglês
10.1021/cm980082e
ISSN1520-5002
AutoresVı́tězslav Zima, Kwang‐Hwa Lii, Ninh Nguyen, A. Ducouret,
Tópico(s)Metal-Organic Frameworks: Synthesis and Applications
ResumoTwo piperazine-templated iron phosphates, (C4H12N2)[Fe4(OH)2(HPO4)5] (1) and (C4H11N2)0.5[Fe3(HPO4)2(PO4)(H2O)] (2), have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, Mössbauer 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) Å, β = 102.601(2)°, V = 1032.0(3) Å3 and Z = 2. The 3-D framework structure consists of layers of iron phosphate which are pillared through HPO4 groups to generate intersecting 8-ring channels with piperazinium dications at the intersections of these channels. Each layer contains infinite chains of edge-sharing FeIIO6 octahedra which are connected to each other via corner-sharing FeIIIO6 octahedra and HPO4 groups. Compound 2 crystallizes in the monoclinic space group C2/c (no. 15) with a = 30.8924(4), b = 6.3733(1), c = 12.5552(2) Å, β = 101.946(1)°, V = 2418.41(7) Å3, and Z = 8. The compound has a layered structure with piperazinium monocations in the interlayer space. Each layer consists of a dimer of edge-sharing octahedra with the composition FeIIFeIIIO10 which shares edges with four FeIIO5 trigonal bipyramids to form a hexamer as the building unit. Each such hexamer is connected to others by corner sharing and through phosphate groups. Both compounds are mixed-valence as indicated from bond valence calculations, Mössbauer measurements, and electric field gradient calculations.
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