CO2 adsorption of three isostructural metal-organic frameworks depending on the incorporated highly polarized heterocyclic moieties.

A systematic investigation of CO2 adsorption behavior in three metal-organic frameworks was executed. The three MOFs adopted the same NbO-type structure, except that the organic ligands were grafted with different highly polarized heterocyclic moieties, namely, oxadiazole, thiadiazole, and selenadiazole, respectively. After activation, the three MOF materials, ZJNU-41a showed different surface areas and pore volumes depending on the incorporated heterocyclic rings attached to the organic ligands as well as the MOF's stabilities. Among the three MOF materials, exhibited an impressive CO2 uptake capacity of 97.4 cm(3) (STP) g(-1) at 298 K and 1 atm, which is comparable and even superior to those reported in NbO-type MOFs. In particular, when the molecular dipole of the attached heterocyclic moieties increases, the CO2 uptake also increases, which was further supported by comprehensive quantum chemical calculations. This work demonstrates that the introduction of highly polarized heterocyclic functional groups into frameworks is a promising approach to target porous metal-organic framework materials with improved CO2 adsorption performance.

Synthesis, Characterization, and Luminescence Modulation of a Metal-Organic Framework Based on a Cyclotriphosphazene-Functionalized Multicarboxylate Ligand.

By using a multicarboxylate ligand consisting of six peripheral 1,3-benzenedicarboxylalte units connected to the central cyclotriphosphazene ring through a P-O-C spacer, a novel metal-organic framework, [Cd5 L(H2 O)4 ]⋅2 (CH3 )2 NH2 ⋅6 DMF (L=hexakis(3,5-dicarboxylatephenyloxy)cyclotriphosphazene), was solvothermally synthesized and characterized by single-crystal and powder XRD, thermal gravimetric analysis, and IR and photoluminescence spectroscopy. Single-crystal XRD analyses show that the framework is an anionic 3D network assembled from pentanuclear [Cd5 (COO)10 ] secondary building units and organic linkers. TOPOS software analyses indicate that two alternative simplifications based on the organic linkers can produce five-connected uninodal bnn-type topology or novel (2,3,6,10)-connected five-nodal topology. Additionally, it is interesting that the luminescence intensity of the complex can be modulated by postsynthetic ion exchange. This study highlights that cyclotriphosphazene-functionalized multicarboxylates, with the combined advantages of conformation diversity and easy functionalization, are a promising type of organic ligand for the synthesis of metal-organic frameworks with fascinating structures and interesting properties.

Merging open metal sites and Lewis basic sites in a NbO-type metal-organic framework for improved C2H2/CH4 and CO2/CH4 separation.

A new three-dimensional NbO-type porous metal-organic framework ZJNU-47 was synthesized via a solvothermal reaction of Cu(NO3)2·3H2O and a Lewis basic nitrogen donor site-rich tetracarboxylate, namely, 5,5'-(pyridazine-3,6-diyl)-diisophthalate, and the structure was characterized by single-crystal X-ray diffraction to be isostructural with NOTT-101. With the synergistic effect of open metal sites, Lewis basic sites and a suitable pore space, the MOF material ZJNU-47a after activation can take up a large amount of C2H2 and CO2. The gravimetric C2H2 uptake of 214 cm(3) (STP) g(-1) at room temperature and 1 atm is the highest among all reported MOFs to date, and the gravimetric CO2 uptake of 108 cm(3) (STP) g(-1) is also among the highest reported for MOFs. Compared to the isostructural MOF NOTT-101a, ZJNU-47a exhibits a significant increase in C2H2 and CO2 uptake and thus improved C2H2/CH4 and CO2/CH4 separations. Significantly, comprehensive DFT studies of C2H2 and CO2 adsorption have revealed that the open nitrogen donor sites are comparable and even superior to open metal sites regarding the adsorption sites. This work demonstrated that the simultaneous introduction of Lewis basic nitrogen donor sites and Lewis acidic metal sites into the framework is a promising approach to improve the gas sorption toward CO2 and C2H2 and thus to produce materials possessing enhanced C2H2/CH4 and CO2/CH4 separation performance.

A NbO-type metal-organic framework exhibiting high deliverable capacity for methane storage.

A copper-based NbO-type metal-organic framework constructed from a tetracarboxylate incorporating phenylethyne as a spacer exhibited an exceptionally high methane working capacity of 184 cm(3) (STP) cm(-3) for methane storage. The value is among the highest reported for MOF materials.

Enhanced CO2 sorption and selectivity by functionalization of a NbO-type metal-organic framework with polarized benzothiadiazole moieties.

A new NbO-type metal-organic framework ZJNU-40 incorporating highly polarized benzothiadiazole moieties exhibits a high CO2 uptake of 108 cm(3) g(-1) at 296 K and 1 atm, as well as good adsorption selectivities of CO2 over CH4 and N2 at room temperature, which is superior to that of the analogous MOF NOTT-101.