Journal
CHEMISTRY-AN ASIAN JOURNAL
Volume 6, Issue 11, Pages 3084-3096Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/asia.201100290
Keywords
magnetic properties; metal-organic frameworks; phase transitions; template synthesis; X-ray diffraction
Categories
Funding
- NSFC [20871007, 20821091]
- National Basic Research Program of China [2006CB601102, 2009CB929403]
- CNRS, France
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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=N,N'-dimethylethylenediamine; M=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 iso-structural and crystallize in the trigonal space group P (3) over bar 1c, 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 Cu2+ 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.
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