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Unprecedented (4,6)-Connected Net with Mixed-Valence M2IIMIII Trinuclear and M6II Hexanuclear Clusters (M = Ni, Co): Syntheses, Crystal Structures, and Magnetic Properties

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journal contribution
posted on 05.09.2017, 00:00 by Lu Zhai, Zhu-Xi Yang, Wen-Wei Zhang, Jing-Lin Zuo, Xiao-Ming Ren
Two new cluster-based metal–organic frameworks (MOFs), {(M3OH)2[(M6O­(OH)2(H2O)2]1.5(EBTC)6}·solvent (M = Ni and Co for 1 and 2, respectively), have been synthesized using a solvothermal reaction, where H4EBTC represents 1,1′-ethynebenzene-3,3′,5,′-tetracarboxylic acid. The isostructural 1 and 2 crystallize in the hexagonal space group P6/mmm, containing class III mixed-valence Ni2IINiIII/Co2IICoIII trinuclear and Ni6II/Co6II hexanuclear secondary building units (SBUs). Both SBUs possess the perfectly planar μ3-O2– and μ4-O2– bridging mode, respectively. In 1 and 2, two trinuclear and three hexanuclear clusters form a cage with the dimensions of ca. 5.0 × 5.0 × 7.8 Å3, which align into a bamboo-like structure through sharing the trinuclear clusters along the c-axis, and form a honeycomb-like structure via sharing the hexanuclear clusters on the plane parallel to the crystallographic (001) plane. In addition, the magnetic properties have been further investigated for two MOFs, disclosing that the weakly antiferromagnetic couplings dominate between the metal ions and no valence ordering occurs even at 2 K.