摘要
The mixed-valence iron phosphates 1∞{[C4N2H11.6] 1.5[FeII FeIII(PO4)(H0.8 PO4)2]·H2O} (1) and 3∞[FeII5FeIII2 (PO4)2-(H0.5PO4) 4] (2) have been synthesized by hydrothermal methods. Their crystal structures were determined by single-crystal X-ray diffraction and Mössbauer spectroscopy. Mössbauer spectroscopy suggests the Fe centers in compound 1 to be mostly in a trapped, mixed-valence +2 and +3 oxidation state from which the average protic hydrogen occupation on HPO4 and piperazinedium is calculated to be 0.8. At 4 K there is an intervalence tunneling process between part of the Fe2+ and Fe3+ atoms. Compound 1 contains linear strands of corner-sharing {FeO4} and {PO4} tetrahedra. The Fe atoms are bridged by Fe-O-P-O-Fe and Fe-O-Fe linkages. The strands are held together by hydrogen bonding interactions involving the piperazinedium and the water molecules of crystallization as well as complementary H-bonds between the HPO4-groups. The iron phosphate 2 is found from Mössbauer spectroscopy to be a trapped mixed-valence system with about 30% Fe3+/70% Fe2+ which translates perfectly into FeII5 FeIII2 from which a total of two protic hydrogens on phosphate has been calculated. The crystal quality permitted the protic hydrogens in 1 and 2 to be found and their positions freely refined. At 4.2 K the Fe3+ is completely and Fe2+ partially magnetically ordered in 2. Compound 2 is a three-dimensional framework constructed from edge- and corner-sharing {FeO6} octahedra and {FeO5} trigonal bipyramids together with the {PO4} tetrahedra. Temperature-variable magnetic measurements confirm the oxidation state assignments for 1 and 2 through a matching experimental and calculated value for μeff at 300 K.
源语言 | 英语 |
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页(从-至) | 2815-2823 |
页数 | 9 |
期刊 | Dalton Transactions |
期 | 14 |
DOI | |
出版状态 | 已出版 - 21 7月 2003 |
已对外发布 | 是 |