Spin Crossover Phenomenon Accompanying Order-Disorder Phase Transition in the Ligand of [FeII(DAPP)(abpt)](ClO4)2 Compound (DAPP = Bis(3-aminopropyl)(2-pyridylmethyl)a

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• 作者：Yuji Miyazaki ; Tadahiro Nakamoto ; Satoaki Ikeuchi ; Kazuya Saito ; Akira Inaba ; Michio Sorai ; Takeo Tojo ; Tooru Atake ; Galina S. Matouzenko ; Samir Zein ; Serguei A. Borshch
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：November 1, 2007
• 年：2007
• 卷：111
• 期：43
• 页码：12508 - 12517
• 全文大小：1012K
• 年卷期：v.111,no.43(November 1, 2007)
• ISSN：1520-5207

文摘

The spin crossover phenomenon of the recently described spin crossover complex [Fe^II(DAPP)(abpt)](ClO₄)₂[DAPP = bis(3-aminopropyl)(2-pyridylmethyl)amine, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole]accompanying an order-disorder phase transition of the ligand was investigated by adiabatic heat capacitycalorimetry, far-IR, IR, and Raman spectroscopies, and normal vibrational mode calculation. A large heatcapacity peak due to the spin crossover transition was observed at T_trs = 185.61 K. The transition enthalpyand entropy amounted to _trsH = 15.44 kJ mol^-1 and _trsS = 83.74 J K^-1 mol^-1, respectively. The transitionentropy is larger than the expected value 60.66 J K^-1 mol^-1, which is contributed from the spin multiplicity(R ln 5; R: the gas constant), disordering of the carbon atom of the six-membered metallocycle in the DAPPligand, and one of the two perchlorate anions (2R ln 2), and change of the normal vibrational modes betweenthe high-spin (HS) and low-spin (LS) states (35.75 J K^-1 mol^-1). The remaining entropy would be ascribedto changes of the lattice vibrations and molecular librations between the HS and LS states. Furthermore,[Fe(DAPP)(abpt)](ClO₄)₂ crystals disintegrated and became smaller crystallites whenever they experiencedthe phase transition. This may be regarded as a successive self-grinding effect, evidenced by adiabaticcalorimetry, DSC, magnetic susceptibility, and microscope observation. The relationship between the crystalsize and the physical quantities is discussed.