Spin Frustration in a Family of Pillared Kagomé Layers of High-Spin Cobalt(II) Ions

• Published in: Chemistry : a European journal 2015-02, Vol.21 (6), p.2560-2567
• Main Authors: Wang, Long-Fei, Li, Cui-Jin, Chen, Yan-Cong, Zhang, Ze-Min, Liu, Jiang, Lin, Wei-Quan, Meng, Yan, Li, Quan-Wen, Tong, Ming-Liang
• Format: Article
• Language: English
• Subjects: Chemistry; cobalt; Cobalt - chemistry; Crystallography, X-Ray; Frustration; Ground state; Interlayers; Ions - chemistry; Joining; layered compounds; Ligands; Magnetic properties; Magnetics; metal-organic frameworks; Molecular Conformation; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Pillars; Pyridines - chemistry; Quantum Theory; spin frustration; Structural analysis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201404847

Based on the analogous kagomé [Co3(imda)2] layers (imda=imidazole‐4,5‐dicarboxylate), a family of pillar‐layered frameworks with the formula of [Co3(imda)2(L)3]⋅(L)n⋅xH2O (1: L=pyrazine, n=0, x=8; 2: L=4,4′‐bipyridine, n=1, x=8; 3: L=1,4‐di(pyridin‐4‐yl)benzene, n=1, x=13; 4: L=4,4′‐di(pyridin‐4‐yl)‐1,1′‐biphenyl, n=1, x=14) have been successfully synthesized by a hydrothermal/solvothermal method. Single‐crystal structural analysis shows a significant increase in the interlayer distances synchronized with the extension of the pillar ligands, namely, 7.092(3) (1), 10.921(6) (2), 14.780(5) (3), and 19.165(4) Å (4). Despite the wrinkled kagomé layers in complexes 2–4, comprehensive magnetic characterizations revealed weakening of interlayer magnetic interactions and an increase in the degree of frustration as the pillar ligand becomes longer from 1 to 4; this leads to characteristic magnetic ground states. For compound 4, which has the longest interlayer distance, the interlayer interaction is so weak that the magnetic properties observed within the range of temperature measured would correspond to the frustrated layer. Opposite of relaxed: A comprehensive magnetic study has been performed on a family of pillar‐layered frameworks with a frustrated kagomé [Co3(imda)2] layer. The increase of interlayer distance weakens interlayer coupling, and thus, strengthens intralayer spin frustration (see figure).