Topological Identification Of The First Uninodal 8-Connected Lsz Mof Built From 2,2 '-Difluorobiphenyl-4,4 '-Dicarbo-Xylate Pillars And Cadmium(Ii)-Triazolate Layers

Using polynuclear metal clusters as nodes, many high-symmetry high-connectivity nets, like 8-connnected bcu and 12-connected fcu, have been attained in metal-organic frameworks (MOFs). However, construction of low-symmetry high-connected MOFs with a novel topology still remains a big challenge. For example, a uninodal 8-connected lsz network, observed in inorganic ZrSiO4, has not been topologically identified in MOFs. Using 2,2'-difluorobiphenyl-4,4'-dicarboxylic acid (H2L) as a new linker and 1,2,4-triazole (Htrz) as a coligand, a novel three-dimensional Cd-II-MOF, namely poly[tetrakis(mu(4)-2,2'-difluorobiphenyl-4,4'-dicarboxylato-kappa O-5(1),O-1':O-1':O-4:O-4') tetrakis(N, N-dimethylformamide-kappa O) tetrakis(mu(3)-1,2,4-triazolato-mu(3) N-1:N-2 :N-4) hexacadmium(II)], [Cd-6(C14H6F2O4)(4)(C2H2N3)(4)(C3H7NO)(4)](n), (I), has been prepared. Single-crystal structure analysis indicates that six different Cd-II ions co-exist in (I) and each Cd-II ion displays a distorted [CdO4N2] octahedral geometry with four equatorial O atoms and two axial N atoms. Three Cd-II ions are connected by four carboxylate groups and four trz(-) ligands to form a linear trinuclear [Cd-3(COO)(4)(trz)(4)] cluster, as do the other three Cd-II ions. Two Cd-3 clusters are linked by trz(-) ligands in a mu(1,2,4)-bridging mode to produce a two-dimensional Cd-II-triazolate layer with (6,3) topology in the ab plane. These two-dimensional layers are further pillared by the L2- ligands along the c axis to generate a complicated three-dimensional framework. Topologically, regarding the Cd-3 cluster as an 8-connected node, the whole architecture of (I) is a uninodal 8-connected lsz framework with the Schlafli symbol (4(22).6(6)). Complex (I) was further characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, thermogravimetric analysis and a photoluminescence study. MOF (I) has a high thermal and water stability.