Construction of Robust Open Metal−Organic Frameworks with Chiral Channels and Permanent Porosity

Abstract

Four new metal-organic frameworks (MOFs) containing chiral channels have been synthesized using an achiral, triazine-based trigonal-planar ligand, 4,4',4' '-s-triazine-2,4,6-triyltribenzoate (TATB), and an hourglass secondary building unit (SBU): Zn3(TATB)2(H2O)2.4DMF.6H2O (1); Cd3(TATB)2(H2O)2.7DMA.10H2O (2); [H2N(CH3)2][Zn3(TATB)2(HCOO)].HN(CH3)2.3DMF.3H2O (3); [H2N(CH3)2][Cd3(TATB)2(CH3COO)].HN(CH3)2.3DMA.4H2O (4). MOFs 1 and 2 are isostructural and possess (10,3)-a nets containing large chiral channels of 20.93 and 21.23 A, respectively, but are thermally unstable due to the easy removal of coordinated water molecules on the SBU. Replacement of these water molecules by formate or acetate generated in situ leads to 3 and 4, respectively. Formate or acetate links SBUs to form infinite helical chains bridged by TATB to create three-dimensional anionic networks, in which one of the two oxygen atoms of the formate or acetate is uncoordinated and points into the void of the channels. This novel SBU-stabilization and channel-functionalization strategy may have general implications in the preparation of new MOFs. Thermogravimetric analysis (TGA) shows that solvent-free 3' is thermally stable to 410 degrees C, while TGA studies on samples vapor-diffused with water, methanol, and chloroform show reversible adsorption. MOF 3 also has permanent porosity with a large Langmuir surface area of 1558 m2/g. All complexes exhibit similar strong luminescence with a lambdamax of approximately 423 nm upon excitation at 268.5 nm.

Chiral Metal-Organic Porous Materials: Synthetic Strategies and Applications in Chiral Separation and Catalysis

“…As a chiral network itself is noncentrosymmetric, chiral coordination polymers are potentially useful as second order NLO-active materials as well as ferroelectric materials. The SHG responses of most reported chiral coordination polymers are same or less than that of urea [94][95][96][97][98] . However, there are a handful of examples, which show stronger SHG response.…”

“…A number of chiral coordination polymers show nonlinear optical activity and ferroelectric behavior [94][95][96][97][98] . The essential criterion for a compound to show either nonlinear optical activity or ferroelectric activity is that the material needs to crystallize in a noncentrosymmetric space group belonging to the polar point groups.…”

“…However, there are a handful of examples, which show stronger SHG response. For example, [H 2 N(CH 3 ) 2 ][Zn 3 (TATB) 2 (HCOO)] ( 30 ) (TATB = 4,4 ¢ ,4″-s -triazine-2,4,6-triyltribenzoate) has three times greater SHG response than urea [98] . A ferroelectric material is one that can be switched rapidly between different states by means of an external electric field.…”

“…However, magnetism [100][101][102][103][104] and photoluminescence [105,106] are two other important physical properties, which are often found in chiral coordination polymers but do not intrinsically depend on chirality of the material. It is interesting to note that often more than one of the above mentioned properties coexists in many chiral coordination polymers [94][95][96][97][98]105] . The reader is directed to the [107] .…”

Large Tripodal Spacer Ligands for the Construction of Microporous Metal–Organic Frameworks with Diverse Structures and Photocatalytic Activities

“…); [18][19][20] 2) flexible dicarboxylic acids system,including succinic acid, glutaric acid (glu), sebacic acid (seb), and suberic acid; [21][22][23][24] 3) rigid-flexible polycarboxylate acid systems, including aromatic polycarboxylate acids and aliphatic polycarboxylate acids, such as [Tb 2 (glu)(bta)(H 2 O) 4 ]·H 2 O [25] (bta = benzotriazole) and [Eu(seb) 0.5 (2,5-pydc)(H 2 O)] [26] (2,5-pydc = pyridine-2,5-dicarboxylic acid);a nd 4) rigid polycarboxylate acid/N-heteroatomic ring systems, such as 2,2'-bipyridyl-4,4'-dicarboxylic acid (H 2 BPDC) [27] and adamantane-1,3-dicarboxylic acid (H 2 adc). [28] Somen ew tripodall igands, such as BTB, [29] TATB, [30,31] and BTATB, [32] (BTB = 1,3,5-(triscarboxypheny)benzene; TATB = 4,4',4''-s-triazine-2,4,6-triyltribenzoate;B TATB = 4,4',4''-(benzene-1,3,5-triyltris(azanediy)tribenzoate) have also been synthetized (Scheme S1 in the Supporting Information) to investigate new structural types of complexes with larger porosity.T he size of the 4,4',4''-[(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)]tribenzoic acid (H 3 TATAB) [32] ligand is larger than those of the other tripodal ligandso utlined above.T ot he best of our knowledge,a part from reports by Zhou et al on two complexes, Zn 4 O(TATAB) 2 ·17 DEF·3H 2 O [32] (DEF = N,N-diethylformamide) and Cu 3 (TATAB) 2 (H 2 O) 3 ·8DMF·9H 2 O, [33] .C omplex 2 has a3 Dm icroporous network structure. In addition, the surfacep hotovoltage and photocatalytic activities were also studied.…”