Mesoporous Cages in Chemically Robust MOFs Created by a Large Number of Vertices with Reduced Connectivity

Abstract

We report the design and synthesis of two metal−organic frameworks (MOFs) with permanent porosity, MOF-818 and MOF-919, using a small ditopic organic linker, 1H-pyrazole-4-carboxylic acid (H 2 PyC), 0.4 nm in length. Three mesoporous cages of unprecedented polyhedra are identified in these MOFs, a wuh cage in MOF-818 and yys and liu cages in MOF-919, with diameters of 3.8, 4.9, and 6.0 nm, respectively. The ditopic H 2 PyC linker functions as the edge in the structure, while two types of metal-containing second building units (SBUs) function as the vertices. 28 vertices are present in the wuh cage; 50 in the yys cage; and 70 in the liu cage. Systematic analysis of these cages along with other mesoporous cages in supramolecules and MOFs constructed by ditopic linkers reveals that the extension of cage size is dictated by both the number and connectivity of the vertices. The increase in cage size is proportional to the number of vertices, while the growth rate is determined by their connectivity. The reduction in connectivity is found to be an effective way to create large cages. All three cages in this report are constructed by three-connecting (3-c) vertices and two-connecting (2-c) vertices. This [2-c, 3-c] connectivity represents the least connectivity required for the construction of cages and the most effective one for cage size expansion. The largest cage, liu, exhibits a cage size to linker size ratio of 15, outstanding in supramolecules and MOFs. MOF-818 is stable in water with a wide pH range (pH = 2−12), and the wuh cage is big enough for the inclusion of biomolecules such as vitamin B 12 and insulin.

Efficient removal of tetracycline hydrochloride from aqueous solution by mesoporous cage MOF-818

“…It should be derived from the decomposition of H 2 PyC concerning the collapse of the MOF-818 framework. Therefore, it can be concluded that the MOF-818 showed good thermal stability below 280 °C, which is consistent with the previous reports [50].…”

“…2a, the data showed an intense peak at 3.09° and five other peaks at 4.96°, 5.80°, 6.05°, 7.00° and 7.60°, which were indexed to the (111), (220), (311), (222), (400) and (331) diffractions, respectively. The diffraction peaks of MOF-818 matched well with the simulated one in the literature [50]. No peaks corresponding to CuO or ZrO 2 were found.…”

“…It can be seen that the obtained MOF-818 samples demonstrated a good nitrogen uptake at the relative pressure P/P 0 < 0.3 and the nitrogen isotherms were corresponded to type IV, which proves the existence of mesopores in the samples. The mesopore diameter calculated by density functional theory (DFT) method was mostly concentrated at 2.95 nm, which was slightly lower than the theoretical value of 3.1 nm calculated by the analysis of crystal structure [50]. A small part of the pore size distributed at 1.59 nm was also found.…”

“…MOF-818 was synthesized according to the literature [50] with modification. ZrOCl 2 ·8H 2 O (212.5 mg, 0.659 mmol), Cu(NO 3 ) 2 ·3H 2 O (620.0 mg, 2.57 mmol), trifluoroacetic acid (600 μL) and H 2 PyC (162.5 mg, 1.45 mmol) were dissolved in 50 mL of DMF by ultrasonic in a 100 mL beaker.…”

“…MOF-818, a new kind of MOF structure with mesoporous cages of unprecedented polyhedra, was reported by H. Deng group in 2018 [50]. The mesoporous cage with the diameter of 3.8 nm is big enough for inclusion of the large size dimensions biomolecules vitamin-B 12 and insulin.…”