Structural, Thermal, and Magnetic Study of Solvation Processes in Spin-Crossover [Fe(bpp)2][Cr(L)(ox)2]2·nH2O Complexes

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• 作者：Miguel Clemente-Le&oacute ; n ; Eugenio Coronado ; M. Carmen Gimé ; nez-L&oacute ; pez ; Francisco M. Romero
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：December 24, 2007
• 年：2007
• 卷：46
• 期：26
• 页码：11266 - 11276
• 全文大小：342K
• 年卷期：v.46,no.26(December 24, 2007)
• ISSN：1520-510X

文摘

The influence of lattice water in the magnetic properties of spin-crossover [Fe(bpp)₂]X₂·nH₂O salts [bpp = 2,6-bis(pyrazol-3-yl)pyridine] is well-documented. In most cases, it stabilizes the low-spin state compared to the anhydrouscompound. In other cases, it is rather the contrary. Unraveling this mystery implies the study of the microscopicchanges that accompany the loss of water. This might be difficult from an experimental point of view. Our strategyis to focus on some salts that undergo a nonreversible dehydration-hydration process without loss of crystallinity.By comparison of the structural and magnetic properties of original and rehydrated samples, several rules concerningthe role of water at the microscopic level can be deduced. This paper reports on the crystal structure, thermalstudies, and magnetic properties of [Fe(bpp)₂][Cr(bpy)(ox)₂]₂·2H₂O (1), [Fe(bpp)₂][Cr(phen)(ox)₂]₂·0.5H₂O·0.5MeOH(2), and [Fe(bpp)₂][Cr(phen)(ox)₂]₂·5.5H₂O·2.5MeOH (3). Salt 1 contains both high-spin (HS) and low-spin (LS)Fe²⁺ cations in a 1:1 ratio. Dehydration yields the anhydrous spin-crossover compound with T_1/2 = 353 K andT_1/2 = 369 K. Rehydration affords the dihydrate [Fe(bpp)₂][Cr(bpy)(ox)₂]₂·2H₂O (1r) with 100% HS Fe²⁺ sites. Salt2 also contains both HS and LS Fe²⁺ cations in a 1:1 ratio. Dehydration yields the anhydrous spin-crossovercompound with T_1/2 = 343 K and T_1/2 = 348 K. Rehydration affords [Fe(bpp)₂][Cr(phen)(ox)₂]₂·0.5H₂O (2r) with72% Fe²⁺ sites in the LS configuration. The structural, magnetic, and thermal properties of these rehydratedcompounds 1r and 2r are also discussed. Finally, 1 has been dehydrated and resolvated with MeOH to give[Fe(bpp)₂][Cr(bpy)(ox)₂]₂·MeOH (1s) with 33% HS Fe²⁺ sites. The influence of the guest solvent in the Fe²⁺ spinstate can anticipate the future applications of these compounds in solvent sensing.