Metal-Organic Niccolite: Synthesis, Structures, Phase Transition, and Magnetic Properties of [CH_(3)NH_(2)(CH_(2))_(2)NH_(2)CH_(3)][M_(2)(HCOO)_(6)] (M velence divalent Mn, Fe, Co, Ni, Cu and Zn)

摘要

We report the synthesis, crystal structures, thermal and magnetic characterizations of a family of metal-organic frameworks adopting the niccolite (NiAs) structure, [dmenH_(2)~(2+)] [M_(2)(HCOO)_(6)~(2-)] (dmen velence N,N'-dimethylethylenediamine; M velence divalent Mn, 1Mn; Fe, 2Fe; Co, 3Co; Ni, 4Ni; Cu, 5Cu; and Zn, 6Zn). The compounds could be synthesized by either a diffusion method or directly mixing reactants in methanol or methanol-water mixed solvents. The five members, 1Mn, 2Fe, 3Co, 4Ni, and 6Zn are isostructural and crystallize in the trigonal space group P31c, while 5Cu crystallizes in C2/c. In the structures, the octahedrally coordinated metal ions are connected by anti-anti formate bridges, thus forming the anionic NiAs-type frameworks of [M_(2)(HCOO)_(6)~(2-)], with dmenH_(2)~(2+) located in the cavities of the frameworks. Owing to the Jahn-Teller effect of the Cu~(2+) ion, the 3D framework of 5Cu consists of zigzag Cu-formate chains with Cu-OCHO-Cu connections through short basal Cu-O bonds, further linked by the long axial Cu-O bonds. 6Zn exhibits a phase transition probably as a result of the order-disorder transition of the dmenH_(2)~(2+) cation around 300 K, confirmed by differential scanning calorimetry and single crystal X-ray diffraction patterns under different temperatures. Magnetic investigation reveals that the four magnetic members, 1Mn, 2Fe, 3Co, and 4Ni, display spin-canted antiferromagnetism, with a Neel temperature of 8.6 K, 19.8 K, 16.4 K, and 33.7 K, respectively. The Mn, Fe, and Ni members show spin-flop transitions below 50 kOe. 2Fe possesses a large hysteresis loop with a large coercive field of 10.8 kOe. The Cu member, 5Cu, shows overall antiferromagnetism (both inter- and intra-chains) with low-dimensional characteristics.