Proton Order－Disorder Phenomena in a Hydrogen-Bonded Rhodium－η5-Semiquinone Complex: A Possible Dielectric Response Mechanism
Proton Order－Disorder Phenomena in a Hydrogen-Bonded Rhodium－η5-Semiquinone Complex: A Possible Dielectric Response Mechanism
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氢键铑－η5-半醌配合物中的质子有序－无序现象：一种可能的介电响应机制
DOI：
10.1002/chem.201500796
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
and Kazuhiro Nakasuji
中科院分区：
文献类型：
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作者：
Minoru Mitsumi;Kazunari Ezaki;Yuuki Komatsu;Koshiro Toriumi;Tatsuya Miyatou;Motohiro Mizuno;Nobuaki Azuma;Yuji Miyazaki;Motohiro Nakano;Yasutaka Kitagawa;Takayasu Hanashima;Ryoji Kiyanagi;Takashi Ohhara;and Kazuhiro Nakasuji
新合成的一维氢键(H键)Rh(II)-η5-半喹酮配合物[Cp*Rh(η5-p-HSq-Me)]Pf6([1]Pf6；Cp*=1，2，3，4，5-五甲基环戊二烯；HSq=半喹酮)在237.1 K出现顺电-反铁电二级相变。相变是由这种质子无序以及Cp*环和Pf6−离子的转动或振动引起的。在RT阶段，沿H键链的相对介电常数εb‘达到相对较高的值(约130)。~(13)C-CP/MAS核磁共振谱的温度依赖性表明，质子在RT相中处于动态无序状态，在低温(LT)相中已经发生了质子交换。在2 40-2 70−K的温度范围内，质子交换的速率常数估计为10−4-10 6s。密度泛函理论计算预测，[1]+的质子化/去质子化导致半醌配体的亲和性发生有趣的变化，同时伴随着π键合的Rh片段的还原/氧化，分别产生稳定的η6对苯二酚配合物[CP*Rh3+(η6-p-H2q-ME4)]2+([2]2+)和η4-苯二酚配合物[CP*Rh+(η4-p-BQ-ME4)]([3])。根据[2]、[2+]和[3]组成的质子孤子在氢键链中的迁移，讨论了导致介电响应的可能机制。
A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η5‐semiquinone complex, [Cp*Rh(η5‐p‐HSQ‐Me4)]PF6([1]PF6; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6−ion. The relative permittivityεb′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of13C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10−4–10−6s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [1]+leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η6‐hydroquinone complex, [Cp*Rh3+(η6‐p‐H2Q‐Me4)]2+([2]2+), and η4‐benzoquinone complex, [Cp*Rh+(η4‐p‐BQ‐Me4)] ([3]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [2]2+and [3], which would be generated in the H‐bonded chain.