Dielectric properties induced by the framework in the hybrid organic-inorganic compounds M(dca)₂pyz M = Fe, Co and Zn

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• 作者：A. Garcí ; a-Ferná ; ndez^a ; J.M. Bermú ; dez-Garcí ; a^a ; S. Castro-Garcí ; a^a ; R. Artiaga^b ; J. Ló ; pez-Beceiro^b ; M.A. Señ ; arí ; s-Rodrí ; guez^a ; M. Sá ; nchez-Andú ; jar^a ; ^{msanchez@udc.es" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Hybrid organic&ndash ; inorganic materials ; Interpenetrated frameworks ; Phase transitions ; Dielectric properties ; Multiferroic materials
• 刊名：Polyhedron
• 出版年：2016
• 出版时间：16 August 2016
• 年：2016
• 卷：114
• 期：Complete
• 页码：249-255
• 全文大小：2454 K

文摘

In this work we prepare and study the M(dca)₂pyz compounds, where dca = polar dicyanamide N(CN)₂⁻ ligand, pyz = pyrazine (C₄H₄N₂) ligand and M = Fe²⁺, Co²⁺ and Zn²⁺ that, according to DSC display a first order phase transition, at T_t ∼ 270 K (Fe), ∼250 K (Co) and ∼240 K (Zn). Very interestingly these compounds, which consist of a rather robust framework with incorporated polar dca ligands, and which does not host guest species in the cavities of the structure, display a dielectric anomaly associated to such phase transition. This latter in fact corresponds to the structural transition from the disordered HT-phase (space group Pnma) to the ordered LT-phase (space group P2₁/n). From a detailed analysis of the dipole distributions in each of these crystal structures we conclude that the polar dca ligands, which bridge two transition metal cations, display a cooperative electrical arrangement, in which the dipoles of each of the two interpenetrated networks show a ferroelectric (FE) arrangement; nevertheless, the relative antiparallel orientation of both networks finally results in net antiferroelectric (AFE) arrangements both in the LT- and HT-polymorphs. Very interestingly, the dynamic disorder of the dca ligands at T_t gives rise to the observed dielectric anomaly. These materials constitute, therefore, an example of hybrid organic–inorganic compounds where the dielectric response directly arises from the framework –and not from polar guest species– which is a very interesting and novel approach in the search for materials in which the dielectric and magnetic properties can couple more strongly.