University of Augsburg, Institute of Physics, Chair of Solid State and Materials Chemistry, Universitätsstrasse 1, 86159 Augsburg, Germany.
Dalton Trans. 2018 Jul 3;47(26):8779-8786. doi: 10.1039/c8dt01185k.
The synthesis and crystal structure of a novel metal organic framework, constructed from MnIII, the 4,4'-bipyrazolate (BPZ) ligand and bridging hydroxyl groups is presented in this work. The network topology is identical to M-CFA-6 (M = Fe, Ga), but in the case of Mn-CFA-6, the structure crystallizes in the monoclinic crystal system due to the Jahn-Teller effect of the high spin d4 manganese(iii) centers. Thermal treatment of Mn-CFA-6 leads to decomposition of the framework above 150 °C. The porosity of Mn-CFA-6 was measured by carbon dioxide sorption, since solvent exchange and removal of the occluded solvent molecules leads to a compression of the pores. Electronic spectra of Mn-CFA-6 reveal two distinct absorption bands that are assigned to the two different manganese(iii) centers as revealed by the single crystal structure analysis. Furthermore, SQUID measurements exhibit ferromagnetic behaviour of Mn-CFA-6 below the magnetic ordering at 45 K and antiferromagnetic coupling above this temperature. Evaluation of the paramagnetic region by the Curie-Weiß formula reveals an effective moment of 4.8μB, which is very close to the spin-only value of MnIII centers.
本工作报道了一种新型金属有机骨架的合成和晶体结构，该骨架由 MnIII、4,4'-联吡啶（BPZ）配体和桥连羟基组成。该网络拓扑结构与 M-CFA-6（M = Fe、Ga）相同，但在 Mn-CFA-6 的情况下，由于高自旋 d4 锰（iii）中心的 Jahn-Teller 效应，结构结晶为单斜晶系。Mn-CFA-6 的热分解在 150°C 以上导致框架分解。通过二氧化碳吸附测量了 Mn-CFA-6 的孔隙率，因为溶剂交换和被封闭溶剂分子的去除会导致孔隙压缩。Mn-CFA-6 的电子光谱显示出两个不同的吸收带，这归因于单晶结构分析揭示的两个不同的锰（iii）中心。此外，SQUID 测量表明 Mn-CFA-6 在 45 K 下的磁有序以下表现出铁磁行为，在高于该温度的磁有序以上表现出反铁磁耦合。通过居里-外斯公式对顺磁区的评估表明有效磁矩为 4.8μB，非常接近 MnIII 中心的自旋-only 值。
