Multiferroicity and magnetodielectric coupling in metal-organic-frameworks (MOFs) is rare and so far restricted mainly to formate-based systems with perovskite structure. In the course of this work we designed a tetragonal framework [Co(C16H15N5O2)], exhibiting spin-chains of Co2+ ions, which are bridged by an organic linker containing a dipolar nitrobenzene moiety. This compound shows relaxor-like ferroelectricity at 100 K, which is followed by the onset of complex magnetic order at 15 K, indicative of weak ferromagnetism. The clear anomaly of the dielectric constant at the magnetic ordering transition indicates magnetodielectric coupling, which is also confirmed by magnetic-field dependent dielectric measurements. Weak ferromagnetism and magnetodielectric coupling, both probably result from a significant Dzyaloshinskii-Moriya interaction, which cants the spin structure and locally breaks inversion symmetry. We document that the introduction of dipolar nitrobenzene as building block in the crystal structure paths the way to design new multiferroic and magnetodielectric MOFs.

中文翻译：

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非钙钛矿金属-有机骨架中的磁电耦合

金属-有机框架（MOF）中的多铁性和磁电耦合很少见，迄今为止主要限于具有钙钛矿结构的基于甲酸盐的体系。在这项工作的过程中，我们设计了一个四方框架[Co（C16H15N5O2）]，该框架具有Co2 +离子的自旋链，该链通过含有偶极硝基苯部分的有机连接基桥接。该化合物在100 K时显示出类似弛豫的铁电，随后在15 K时开始出现复杂的磁序，表明铁磁性弱。磁有序跃迁处介电常数的明显异常表明磁电耦合，这也通过与磁场有关的介电测量得到证实。弱的铁磁性和磁电耦合，可能都是由于Dzyaloshinskii-Moriya相互作用引起的，倾斜自旋结构并局部破坏反演对称性。我们记录了在晶体结构中引入偶极硝基苯作为结构单元的路径，为设计新的多铁性和磁电性MOF提供了途径。