Two New Mixed-Valence Iron Phosphates Templated by Piperazine: (C4H12N2)[Fe4(OH)2(HPO4)5] and (C4H11N2)0.5[Fe3(HPO4)2(PO4)(H2O)

Abstract

Two 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, 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) A, β = 102.601(2)°, V = 1032.0(3) A3 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) A, β = 101.946(1)°, V = 2418.41(7) A3, and Z = 8. The compound has a layered structure...