Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, People's Republic of China.
Inorg Chem. 2013 Aug 19;52(16):9356-62. doi: 10.1021/ic400927m. Epub 2013 Aug 6.
A clear understanding of the origin of magnetism in metal-organic frameworks (MOFs) would provide useful insight for tuning the electromagnetic properties of MOFs and finding new applications. In the present study, first-principles calculations show that the open paramagnetic metal sites in three-dimensional porous magnets M-MOF-74 (M = Ni, Co, Fe, Mn) favor high-spin electronic arrangement. Fe- and Co-MOF-74 exhibit ferromagnetic (FM) features and significantly distinct energy gaps between spin-up and spin-down channels in metastable states. After replacement of the Co center with a Ni ion, the FM feature was exhibited for the stable state since the "extra" valence electron was filled in the spin-down 3d bands to shift the Fermi level to higher energy. In contrast, after removal of one valence electron (i.e., replacement of the Fe center with Mn atoms), the energy gap was significantly enlarged and an antiferromagnetic (AFM) feature will be discerned.
清楚了解金属-有机骨架（MOFs）中磁性的起源，将为调整 MOFs 的电磁特性和寻找新的应用提供有用的见解。在本研究中，第一性原理计算表明，三维多孔磁体 M-MOF-74（M = Ni、Co、Fe、Mn）中开放的顺磁金属位点有利于高自旋电子排列。Fe-MOF-74 和 Co-MOF-74 在亚稳态下表现出铁磁性（FM）特征，并且自旋向上和自旋向下通道之间的能隙明显不同。在将 Co 中心替换为 Ni 离子后，由于“额外”价电子填充在自旋向下的 3d 带中，使费米能级移至更高的能量，因此稳定态表现出 FM 特征。相比之下，去除一个价电子（即，用 Mn 原子替换 Fe 中心）后，能隙显著增大，将表现出反铁磁性（AFM）特征。
