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 ZrSiO, has not been topologically identified in MOFs. Using 2,2'-difluorobiphenyl-4,4'-dicarboxylic acid (HL) as a new linker and 1,2,4-triazole (Htrz) as a coligand, a novel three-dimensional Cd-MOF, namely poly[tetrakis(μ-2,2'-difluorobiphenyl-4,4'-dicarboxylato-κO,O:O:O:O)tetrakis(N,N-dimethylformamide-κO)tetrakis(μ-1,2,4-triazolato-κN:N:N)hexacadmium(II)], [Cd(CHFO)(CHN)(CHNO)], (I), has been prepared. Single-crystal structure analysis indicates that six different Cd ions co-exist in (I) and each Cd ion displays a distorted [CdON] octahedral geometry with four equatorial O atoms and two axial N atoms. Three Cd ions are connected by four carboxylate groups and four trz ligands to form a linear trinuclear [Cd(COO)(trz)] cluster, as do the other three Cd ions. Two Cd clusters are linked by trz ligands in a μ-bridging mode to produce a two-dimensional Cd-triazolate layer with (6,3) topology in the ab plane. These two-dimensional layers are further pillared by the L ligands along the c axis to generate a complicated three-dimensional framework. Topologically, regarding the Cd cluster as an 8-connected node, the whole architecture of (I) is a uninodal 8-connected lsz framework with the Schläfli symbol (4·6). 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.

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

“…However, the photoluminescence intensities of MOFs (1) and (2) are obviously increased and red-shifted compared with free HL. This feature is probably attributed to the more rigid conformation and more effective conjugation of the L À ligand due to its coordination in MOFs, which is similar to that found in the related Cd II -MOF (Zhang et al, 2018). In addition, the three emission bands of (2) are due to the three different L À ligands existing in the structure.…”

“…2a). The Cd-O and Cd-N bond lengths are 2.339 (4)-2.484 (3) and 2.318 (4)-2.344 (4) Å , respectively, which are similar to those of a related Cd II -MOF (Zhang et al, 2018). Each Cd II ion is linked to four adjacent Cd II ions via four L À ligands and can be treated topologically as a 4-connected node (Fig.…”

“…The asymmetric or symmetric stretching vibrations of the carboxylate groups in (1)-(3) are observed around 1610 or 1403 cm À1 , respectively. The absence of very strong absorption bands around 1700 cm À1 confirms the complete deprotonation of the carboxyl group of HL during the reactions (Zhang et al, 2018). The bands at 3420 [for 1 can be attributed to the -C O stretching bands of DMF and DMA molecules (Luo et al, 2014).…”

“…Until now, a large number of rigid ligands, such as biphenyl-4,4 0dicarboxylic acid (H 2 BPDC; Moon et al, 2005), biphenyl-3,3 0 ,4,4 0 -tetracarboxylic acid (H 4 BPTC; Hao et al, 2005), have been chosen as organic linkers. Our previous work has also shown that substituted BPDC can be used successfully to construct robust MOFs with sra Wang et al, 2015), lsz (Zhang et al, 2018) and fes topologies (Wang, Zhu et al, 2010). We have also reported that 2,2 0 -dimethoxy-BPDC can be used to build acentric MOFs, which feature an unprecedented 3D/3D hetero-interpenetrating framework consisting of a dia and a bcu topology (Xu et al, 2012;.…”

Two topologically different 3D CuII metal–organic frameworks assembled from the same ligands: control of reaction conditions

“…Carboxylic acids as bridging ligands usually have two advantages: first, carboxylic acids have rich coordination modes with metal ions; secondly, depending on the degree of deprotonation, the carboxyl group itself can act as a hydrogen-bond acceptor and donor (Deacon & Phillips, 1980;Xu et al, 2016;. Based on these considerations, recently, a few novel 3D MOFs with a rare lsz topology (Zhang et al, 2018), a unique binodal 3,20-connected network (Zhao et al, 2016), an unprecedented 3D/3D heterointerpenetrating framework composed of a dia and a bcu topology (Xu et al, 2012;Luo et al, 2014), and an unusual infinite nano-sized ribbon (Zhang et al, 2011) have been successfully assembled from the symmetrically substituted biphenyldicarboxylic acids (H 2 BPDC). In contrast to the carboxylate-based MOFs, however, the sulfonate-based MOFs have been significantly less investigated; in particular, their final structures are often difficult to predict (Shimizu et al, 2009;Zhang et al, 2016;Xu et al, 2015;.…”