Metal-organic frameworks are porous crystalline solids consisting of metal clusters or ions connected by organic linkers. These frameworks can exhibit exceptional gas-storage capacities and adsorptive selectivities; [1] these properties have led to their investigation for a vast number of applications. [2] However, optimization remains difficult because the number of metal-ligand combinations is effectively infinite and because a large number of phases can emerge for even a single choice of metal and ligand. Synthetic reaction conditions play a crucial role in determining which phase precipitates from solution. Thus, preparation of the desired material in a pure, crystalline form relies on extensive systematic screening of many reaction parameters.[3] The modular nature of the solventothermal preparation of metalorganic frameworks makes high-throughput synthesis an effective means for rapidly exploring the parameter space. [4] However, the subsequent characterization of new compounds becomes a bottleneck for this type of workflow since structural characterization by XRD or evaluation of the BET surface area through adsorption measurements are not practical for large numbers of unknown samples. Thus, the development of a tool to analyze porosity that precludes the need to perform labor-intensive tasks (i.e. activation and sorption measurements) on each sample would greatly accelerate the discovery of potentially interesting frameworks by quickly eliminating nonporous or low-surface-area materials that are not of interest.Nuclear magnetic resonance (NMR) relaxometry can potentially provide an initial estimate of the pore volume and surface area of an unknown metal-organic framework. These methods use imbibed fluid nuclei as probes of the internal surface area and have been used extensively to characterize porous media, including rocks, silica, zeolites, cements, and soils.[5] Transverse relaxation (T 2 ) is a process in which observable magnetization decays to equilibrium in an exponential fashion.[6] The relaxation rate of liquid nuclei imbibed in porous media generally depends on the degree of confinement because of interactions with the pore walls [7] and internal field gradients.[8] Although some relaxation studies of hydrocarbon gases in MOF-5 and Cu 3 (BTC) 2 (BTC = benzene-1,3,5-tricarboxylic acid) have been conducted, [9] the relaxation behavior of liquids in metal-organic frameworks and its connection to internal surface area has yet to be studied systematically.Herein, we demonstrate a correlation between the BET surface area and the transverse relaxation (T 2 ) of solventimbibed metal-organic frameworks and zeolites. The use of a liquid probe greatly simplifies sample preparation to washing and filtration, thereby minimizing the amount of necessary automation hardware while eliminating the timeconsuming process of sample isolation and activation. Furthermore, the relaxation measurements described in this study can be performed considerably faster than a typical BET surface area measurement. Lastly, the...
Replacing the PbÀXo ctahedral building unit of A I PbX 3 perovskites (X = halide) with ap air of edge-sharing PbÀXo ctahedra affords the expanded perovskite analogs: A II Pb 2 X 6 .W er eport seven members of this new family of materials.I n3 Dh ybrid perovskites,o rbitals from the organic molecules do not participate in the band edges.Incontrast, the more spacious inorganic sublattice of the expanded analogs accommodates larger pyrazinium-based cations with low-lying p*o rbitals that form the conduction band, substantially decreasing the band gap of the expanded lattice.The molecular nature of the conduction band allows us to electronically dope the materials by reducing the organic molecules.Bysynthesizing derivatives with A II = pyridinium and ammonium, we can isolate the contributions of the pyrazinium-based orbitals in the band gap transition of A II Pb 2 X 6 .T he organic-molecule-based conduction band and the inorganic-ion-based valence band provideanunusual electronic platform with localized states for electrons and more disperse bands for holes upon optical or thermal excitation.
Reduction of the insulating one-dimensional coordination polymer [Cu(abpy)PF 6 ] n , 1a(PF 6 ), (abpy = 2,2'-azobispyridine) yields the conductive,p orous polymer [Cu-(abpy)] n , 2a. Pressed pellets of neutral 2a exhibit aconductivity of 0.093 Scm À1 at room temperature and aB runauer-Emmett-Teller (BET) surface area of 56 m 2 g À1 .Fine powders of 2a have aB ET surface area of 90 m 2 g À1 .C yclic voltammetry shows that the reduction of 1a(PF 6 )t o2a is quasireversible,indicative of facile charge transfer through the bulk material. The BET surface area of the reduced polymer 2 can be controlled by changing the size of the counteranion Xinthe cationic [Cu(abpy)X] n .R eduction of [Cu(abpy)X] n with X = Br (2b)orB Ar F (2c;B Ar F = tetrakis(3,5-bis(trifluoromethyl)phenyl)), affords [Cu(abpy)] n polymers with surface areas of 60 and 200 m 2 g À1 ,respectively.
Reduction of the insulating one-dimensional coordination polymer [Cu(abpy)PF ] , 1 a(PF ), (abpy=2,2'-azobispyridine) yields the conductive, porous polymer [Cu(abpy)] , 2 a. Pressed pellets of neutral 2 a exhibit a conductivity of 0.093 S cm at room temperature and a Brunauer-Emmett-Teller (BET) surface area of 56 m g . Fine powders of 2 a have a BET surface area of 90 m g . Cyclic voltammetry shows that the reduction of 1 a(PF ) to 2 a is quasi-reversible, indicative of facile charge transfer through the bulk material. The BET surface area of the reduced polymer 2 can be controlled by changing the size of the counteranion X in the cationic [Cu(abpy)X] . Reduction of [Cu(abpy)X] with X=Br (2 b) or BAr (2 c; BAr =tetrakis(3,5-bis(trifluoromethyl)phenyl)), affords [Cu(abpy)] polymers with surface areas of 60 and 200 m g , respectively.
Exposure to humid O or ambient air affords a 5-order-of-magnitude increase in electronic conductivity of a new Prussian blue analogue incorporating Co and V-oxo units. Oxidation produces a mixed-valence framework, where the O exposure time controls the V/V ratio and thereby the material's conductivity. The oxidized framework shows an intervalence charge-transfer band at ca. 4200 cm, consistent with mixed valence. The mixed-valence frameworks show semiconducting behavior with conductivity values of 10 S·cm at room temperature and 10 S·cm at 100 °C and activation energies of ca. 0.3 eV. N adsorption measurements at 77 K show that these materials possess permanent porosity before and after oxidation with Brunauer-Emmett-Teller surface areas of 340 and 370 m·g, respectively.
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