Mohammad A. Omary

Fluorous metal-organic frameworks with superior adsorption and hydrophobic properties toward oil spill cleanup and hydrocarbon storage.

We demonstrate that fluorous metal-organic frameworks (FMOFs) are highly hydrophobic porous materials with a high capacity and affinity to C(6)-C(8) hydrocarbons of oil components. FMOF-1 exhibits reversible adsorption with a high capacity for n-hexane, cyclohexane, benzene, toluene, and p-xylene, with no detectable water adsorption even at near 100% relative humidity, drastically outperforming activated carbon and zeolite porous materials. FMOF-2, obtained from annealing FMOF-1, shows enlarged cages and channels with double toluene adsorption vs FMOF-1 based on crystal structures. The results suggest great promise for FMOFs in applications such as removal of organic pollutants from oil spills or ambient humid air, hydrocarbon storage and transportation, water purification, etc. under practical working conditions.

Rigidifying fluorescent linkers by metal-organic framework formation for fluorescence blue shift and quantum yield enhancement.

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 ± 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

Crystallographic Observation of Dynamic Gas Adsorption Sites and Thermal Expansion in a Breathable Fluorous Metal–Organic Framework†

Playing accordion: Cooling a single crystal of a microporous fluorous metal-organic framework under ambient atmosphere leads to very large breathing upon gas adsorption, during which multiple N(2) molecules are filled into channels and cages (see picture). While the framework exhibits remarkable positive thermal expansion under vacuum, a gigantic apparent negative thermal expansion takes place when the crystal is exposed to N(2) at ambient pressure.

Kinetically tuned dimensional augmentation as a versatile synthetic route towards robust metal-organic frameworks.

Metal-organic frameworks with high stability have been pursued for many years due to the sustainability requirement for practical applications. However, researchers have had great difficulty synthesizing chemically ultra-stable, highly porous metal-organic frameworks in the form of crystalline solids, especially as single crystals. Here we present a kinetically tuned dimensional augmentation synthetic route for the preparation of highly crystalline and extremely robust metal-organic frameworks with a preserved metal cluster core. Through this versatile synthetic route, we obtain large single crystals of 34 different iron-containing metal-organic frameworks. Among them, PCN-250(Fe2Co) exhibits high volumetric uptake of hydrogen and methane, and is also stable in water and aqueous solutions with a wide range of pH values.

Luminescent Chains Formed from Neutral, Triangular Gold Complexes Sandwiching TlI and AgI. Structures of {Ag([Au(μ-C2,N3-bzim)]3)2}BF4·CH2Cl2, {Tl([Au(μ-C2,N3-bzim)]3)2}PF6·0.5THF (bzim = 1-Benzylimidazolate), and {Tl([Au(μ-C(OEt)═NC6H4CH3)]3)2}PF6·THF, with MAu6 (M = Ag+, Tl+) Cluster Cores

It has been found that several trinuclear complexes of AuI interact with silver and thallium salts to intercalate Ag+ and Tl+ cations, thereby forming chains. The resulting sandwich clusters center the cations between the planar trinuclear moieties producing structures in which six AuI atoms interact with each cation in a distorted trigonal prismatic coordination. The resultant (B3AB3B3AB3)∞ pattern of metal atoms also shows short (∼3.0 Å) aurophilic interactions between BAB molecular centers. These compounds display a strong visible luminescence, under UV excitation, which is sensitive to temperature and the metal ion interacting with the gold. X-ray crystal structures are reported for Ag([Au(μ-C2,N3-bzim)]3)2BF4·CH2Cl2 (P [Formula: see text] , Z = 2, a = 14.4505(1)Å; b = 15.098(2)Å; c = 15.957(1)Å; α = 106.189(3)°; β = 103.551(5)°; γ = 101.310(5)°); Tl([Au(μ-C2,N3-bzim)]3)2PF6·0.5C4H8O (P [Formula: see text] , Z = 2, a = 15.2093(1)Å; b =15.3931(4)Å; c = 16.1599(4)Å; α = 106.018(1)°; β = 101.585(2)°; γ=102.068(2)°); and Tl([Au(μ-C(OEt)═NC6H4CH3)]3)2PF6·C4H8O (P2(1)/n, Z = 4, a = 16.4136(3)Å; b = 27.6277(4)Å; c = 16.7182(1)Å; β = 105.644(1)°). Each compound shows that the intercalated cation, Ag+ or Tl+, coordinates to a distorted trigonal prism of six AuI atoms. The counteranions reside well apart from the cations between the cluster chains.

Rational Design of Macrometallocyclic Trinuclear Complexes with Superior π-Acidity and π-Basicity

Density functional theory (DFT) has been used to assess the pi-acidity and pi-basicity of metal-organic trimetallic macromolecular complexes of the type [M(mu-L)]3, where M = Cu, Ag, or Au and L = carbeniate, imidazolate, pyridiniate, pyrazolate, or triazolate. The organic compounds benzene, triazole, imidazole, pyrazole, and pyridine were also modeled, and their substituent effects were compared to those of the coinage metal trimers. Our results, based on molecular electrostatic potential surfaces and positive charge attraction energy curves, indicate that the metal-organic macromolecules show superior pi-acidity and -basicity compared to their organic counterparts. Moreover, the metal-organic cyclic trimers are found to exhibit pi-acidity and -basicity that can be systematically tuned both coarsely and finely by judicious variation of the bridging ligand (relative pi-basicity imidazolate > pyridiniate > carbeniate > pyrazolate > triazolate), metal (relative pi-basicity Au > Cu > Ag), and ligand substituents. These computational findings are thus guiding experimental efforts to rationally design novel [M(mu-L)]3 materials for applications in molecular electronic devices that include metal-organic field-effect transistors and light-emitting diodes.

Water Cluster Confinement and Methane Adsorption in the Hydrophobic Cavities of a Fluorinated Metal–Organic Framework

Water cluster formation and methane adsorption within a hydrophobic porous metal organic framework is studied by in situ vibrational spectroscopy, adsorption isotherms, and first-principle DFT calculations (using vdW-DF). Specifically, the formation and stability of H2O clusters in the hydrophobic cavities of a fluorinated metal-organic framework (FMOF-1) is examined. Although the isotherms of water show no measurable uptake (see Yang et al. J. Am. Chem. Soc. 2011 , 133 , 18094 ), the large dipole of the water internal modes makes it possible to detect low water concentrations using IR spectroscopy in pores in the vicinity of the surface of the solid framework. The results indicate that, even in the low pressure regime (100 mTorr to 3 Torr), water molecules preferentially occupy the large cavities, in which hydrogen bonding and wall hydrophobicity foster water cluster formation. We identify the formation of pentameric water clusters at pressures lower than 3 Torr and larger clusters beyond that pressure. The binding energy of the water species to the walls is negligible, as suggested by DFT computational findings and corroborated by IR absorption data. Consequently, intermolecular hydrogen bonding dominates, enhancing water cluster stability as the size of the cluster increases. The formation of water clusters with negligible perturbation from the host may allow a quantitative comparison with experimental environmental studies on larger clusters that are in low concentrations in the atmosphere. The stability of the water clusters was studied as a function of pressure reduction and in the presence of methane gas. Methane adsorption isotherms for activated FMOF-1 attained volumetric adsorption capacities ranging from 67 V(STP)/V at 288 K and 31 bar to 133 V(STP)/V at 173 K and 5 bar, with an isosteric heat of adsorption of ca. 14 kJ/mol in the high temperature range (288-318 K). Overall, the experimental and computational data suggest high preferential uptake for methane gas relative to water vapor within FMOF-1 pores with ease of desorption and high framework stability under operative temperature and moisture conditions.

Luminescent homoatomic exciplexes in dicyanoargenate(I) ions doped in alkali halide crystals. ‘Exciplex tuning’ by site-selective excitation and variation of the dopant concentration

Abstract The photoluminescence spectra of dicyanoargenate(I) ions doped in KCl host crystals show several ultraviolet and visible emission bands. Each emission band becomes dominant at a characteristic excitation wavelength; i.e. the energy of the emission can be tuned. Both the experimental and theoretical results suggest the formation of Ag–Ag bonded excimers and exciplexes between adjacent Ag(CN) 2 − ions in the host lattice. The experimental evidence includes the broadness, the absence of detailed structure, and the low band energies of the luminescent bands. Ab-initio and extended Huckel calculations show that the lowest unoccupied molecular orbital (LUMO) is bonding with respect to Ag–Ag bonds while the highest occupied molecular orbital (HOMO) is antibonding. Further, the calculations indicate the existence of exciplexes with shorter Ag–Ag bond distances, higher binding energies, and larger Ag–Ag overlap populations than the corresponding ground state oligomers. The results in this study give rise to a new optical phenomenon which is called ‘exciplex tuning’. Tuning of the emission over the 285–610 nm wavelength range has been achieved in KCl/Ag(CN) 2 − crystals by site-selective excitation and varying the Ag(CN) 2 − dopant concentration.

Sensitization of naphthalene monomer phosphorescence in a sandwich adduct with an electron-poor trinuclear silver(i) pyrazolate complex.

Facial complexation of naphthalene to {[3,5-(CF(3))(2)Pz]Ag}(3) (Ag(3)) gives rise to a stacked binary adduct (1) that exhibits phosphorescence corresponding to T(1) monomer emission of naphthalene. Crystals and powders of 1 exhibit bright-green phosphorescence at room temperature with a 830 mus lifetime, whereas cooling to cryogenic temperatures increases the intensity, lifetime, and vibronic resolution. The binary adduct exhibits a drastically shorter phosphorescence lifetime of 6.7 ms versus free naphthalene (2.4 s) in a frozen dichloromethane matrix, which results from the external heavy-atom effect of silver. Adduct 1 represents a new class of phosphors containing lighter but more benign silver than mercury atoms in trinuclear d(10) pi-acid complexes as arene triplet sensitizers.

Controlling the carrier recombination zone for improved color stability in a two-dopant fluorophore/phosphor white organic light-emitting diode

A white organic light-emitting diode (WOLED) is produced upon systematic introduction of deep-blue fluorescence from 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl to broad-band yellow phosphorescence from bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) in the common host 4,4′-bis(carbazol-9-yl)biphenyl. The carrier recombination zone is first identified upon investigating alternative device structures, then optimized by varying the thickness of the electron-transport layer. The WOLED exhibits striking stability of color and efficiency, as manifest by parameters at high brightness of 1000 cd/m2 sustaining 94%–122% their values at 50 cd/m2.