Topological identification of the first uninodal 8-connected lsz MOF built from 2,2'-difluorobiphenyl-4,4'-dicarboxylate pillars and cadmium(II)-triazolate layers.

Abstract

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 CdII-MOF, namely poly[tetrakis(μ4-2,2'-difluorobiphenyl-4,4'-dicarboxylato-κ5O1,O1':O1':O4:O4')tetrakis(N,N-dimethylformamide-κO)tetrakis(μ3-1,2,4-triazolato-κ3N1:N2:N4)hexacadmium(II)], [Cd6(C14H6F2O4)4(C2H2N3)4(C3H7NO)4]n, (I), has been prepared. Single-crystal structure analysis indicates that six different CdII ions co-exist in (I) and each CdII ion displays a distorted [CdO4N2] octahedral geometry with four equatorial O atoms and two axial N atoms. Three CdII ions are connected by four carboxylate groups and four trz- ligands to form a linear trinuclear [Cd3(COO)4(trz)4] cluster, as do the other three CdII ions. Two Cd3 clusters are linked by trz- ligands in a μ1,2,4-bridging mode to produce a two-dimensional CdII-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 Cd3 cluster as an 8-connected node, the whole architecture of (I) is a uninodal 8-connected lsz framework with the Schläfli symbol (422·66). 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.