Mixed-Valence Heptanuclear Iron Complexes with Ferromagnetic Interaction

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• 作者：Ivan 艩alitro拧 ; Roman Bo膷a ; Radovan Herchel ; J谩n Moncol ; Ivan Nemec ; Mario Ruben ; Franz Renz
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：December 3, 2012
• 年：2012
• 卷：51
• 期：23
• 页码：12755-12767
• 全文大小：654K
• 年卷期：v.51,no.23(December 3, 2012)
• ISSN：1520-510X

文摘

Three new Prussian blue analogues, heptanuclear mixed-valence iron complexes of the type [Fe^II(CN)₆{Fe^III(1_鈥?H)}₆]Cl₂路nH₂O, were synthesized and structurally and spectrally characterized, and their magnetic properties were investigated (1_鈥?H corresponds to doubly deprotoned Schiff-base pentadentate ligands 1a, N,N鈥?bis(2-hydroxybenzylidene)-1,5-diamino-3-azapentane, 1b, N,N鈥?bis(3-ethoxy-2-hydroxybenzylidene)-1,7-diamino-4-azaheptane, or 1c, N,N鈥?bis(3-methoxy-2-hydroxybenzylidene)-1,6-diamino-3-azahexane). These compounds were formed by assembling the [Fe(CN)₆]^{4鈥?/sup> building block with mononuclear complexes of the [Fe(1_鈥?H)Cl] type. X-ray structure analysis revealed that the complexes adopt a star-like architecture: the Fe(II) ion lies at the very center, and on its octahedral nodes the Fe(III) sites are coordinated in the FeII鈥揅鈮鈥揊eIII manner. The Schiff-base pentadentate ligand moiety 1_鈥?H coordinates a single Fe(III) center in two complexes 3b and 3c. Ligands 1a_鈥?H in the complex cation of 3a adopt an unusual coordination mode: three donor atoms of the same ligand (one O and two N) coordinate one Fe(III), whereas the remaining N鈥?and O鈥?donor atoms coordinate the neighboring Fe(III) center creating the {Fe(ON₂)(N鈥睴鈥?N鈥硙 chromophore involving two 1a_鈥?H ligand moieties. Moreover, three Fe(III) centers are interconnected with three 1a_鈥?H ligands in such a manner that two {FeIII₃(1a_鈥?H)₃} units form two intramolecular rings. Magnetic investigation of the heptanuclear complexes revealed the high-spin state of all six Fe(III) coordination sites (s = 5/2), while the very central Fe(II) site is in the low-spin state (s = 0). At low temperature, the ferromagnetic exchange interactions stay evident for all three complexes. M枚ssbauer spectra of compounds 3a and 3b revealed a presence of two different doublets for both compounds: the major doublet is related to six Fe(III) high-spin coordination sites and the minor doublet refers to the low-spin very central Fe(II).}