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-connnectedbcuand 12-connectedfcu, 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-connectedlsznetwork, 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 CdIIions co-exist in (I) and each CdIIion displays a distorted [CdO4N2] octahedral geometry with four equatorial O atoms and two axial N atoms. Three CdIIions 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 CdIIions. Two Cd3clusters 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 theabplane. These two-dimensional layers are further pillared by theL2−ligands along thecaxis to generate a complicated three-dimensional framework. Topologically, regarding the Cd3cluster as an 8-connected node, the whole architecture of (I) is a uninodal 8-connectedlszframework 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.