ic048986r_si_002.cif (64.91 kB)

Synthesis and Characterization of a Porous Magnetic Diamond Framework, Co3(HCOO)6, and Its N2 Sorption Characteristic

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posted on 07.03.2005 by Zheming Wang, Bin Zhang, Mohamedally Kurmoo, Mark A. Green, Hideki Fujiwara, Takeo Otsuka, Hayao Kobayashi
[Co3(HCOO)6](CH3OH)(H2O) (1), the isostructural analogue of the porous magnet of coordination framework [Mn3(HCOO)6](CH3OH)(H2O), and its desolvated form [Co3(HCOO)6] (2) were prepared and characterized by X-ray and neutron diffraction methods, IR, thermal analyses, and BET, and their magnetic properties were measured. The parent compound, 1, crystallizes in the monoclinic system, space group P21/c, a = 11.254(2) Å, b = 9.832(1) Å, c = 18.108(3) Å, β = 127.222(2)°, V = 1595.5(4) Å3, Z = 4, R1 = 0.0329 at 180 K. It possesses a unit cell volume that is 9% smaller than [Mn3(HCOO)6](CH3OH)(H2O) due to the smaller radius of Co2+ ion. Compared with the parent compound 1, the desolvated compound 2 has slightly larger lattice with cell parameters of a = 11.2858(4) Å, b = 9.8690(4) Å, c = 18.1797(6) Å, β = 127.193(2)°, V = 1613.0(1) Å3, R1 = 0.0356 at 180 K. The cell parameters of 2, obtained from neutron powder data at 2 K, are a = 11.309(2) Å, b = 9.869(1) Å, c = 18.201(3) Å, β = 127.244(8)°, V = 1617.3(5) Å3. The pore volume reduces from 33% to 30% by replacing Mn by Co. The material exhibits a diamond framework based on Co-centered CoCo4 tetrahedral nodes, in which all metal ions have octahedral coordination geometry and all HCOO groups link the metal ions in synsyn/anti modes. It displays thermal stability up to 270 °C. The compound easily loses guest molecules without loss of crystallinity, and it partly reabsorbs water from the atmosphere. Significant N2 sorption was observed for the desolvated framework suggesting that the material possesses permanent porosity. The magnetic properties show a tendency to a 3D long-range magnetic ordering, probably antiferromagnetic with a spin canting arrangement below 2 K.