Metallotectons: Comparison of Molecular Networks Built from Racemic and Enantiomerically Pure Tris(dipyrrinato)cobalt(III) Complexes

The structures of a series of crystalline chiral tris(dipyrrinato)cobalt(III) complexes were determined. The peripheries of the selected complexes bear three trigonally directed substituents known to engage in various intermolecular interactions, including COOH, CN, diaminotriazinyl (DAT), and Br. To allow comparison, structures were determined for both racemic and enantiomerically pure complexes in all cases, except that of the Br-substituted compound. The ability of COOH and DAT groups to participate in well-established patterns of intermolecular hydrogen bonding led to structures with predictable features. In particular, crystallization of the racemic DAT-substituted complex yielded a structure built from open hydrogen-bonded sheets, and a significant fraction of the volume of the crystals (40%) proved to be available for the inclusion of guests. Weaker C−H···N and C−H···Br interactions were observed in the structures of the CN- and Br-substituted complexes, which yielded networks that were found to be more closely packed

Systematic Ligand Modulation Enhances the Moisture Stability and Gas Sorption Characteristics of Quaternary Metal–Organic Frameworks

Complex metal–organic frameworks (MOFs) that maintain high structural order promise sophisticated and tunable properties. Here, we build on our strategy of using combinations of structurally distinct ligands to generate a new isoreticular series of ordered quaternary Zn₄O–carboxylate MOFs. Rational design of the framework components steers the system toward multicomponent MOFs and away from competing phases during synthesis. Systematic ligand modulation led to the identification of a set of frameworks with unusually high stability toward water vapor. These frameworks lose no porosity after 100 days’ exposure to ambient air or 20 adsorption–desorption cycles up to 70% relative humidity. Across this series of frameworks, a counterintuitive relationship between the length of pendant alkyl groups and framework stability toward water vapor emerges. This phenomenon was probed via a series of gas and vapor adsorption experiments together with Grand Canonical Monte Carlo (GCMC) simulations, and could be rationalized on the basis of the propensity of the frameworks to adsorb water vapor and the proximity of the adsorbed water molecules to the water-sensitive metal clusters. Systematic variation of the pore volume and topography also tunes the CO₂ and CH₄ gas adsorption behavior. Certain of these materials display increases in their adsorption capacities of 237% (CO₂) and 172% (CH₄) compared to the parent framework

Metallotectons: Comparison of Molecular Networks Built from Racemic and Enantiomerically Pure Tris(dipyrrinato)cobalt(III) Complexes

The structures of a series of crystalline chiral tris(dipyrrinato)cobalt(III) complexes were determined. The peripheries of the selected complexes bear three trigonally directed substituents known to engage in various intermolecular interactions, including COOH, CN, diaminotriazinyl (DAT), and Br. To allow comparison, structures were determined for both racemic and enantiomerically pure complexes in all cases, except that of the Br-substituted compound. The ability of COOH and DAT groups to participate in well-established patterns of intermolecular hydrogen bonding led to structures with predictable features. In particular, crystallization of the racemic DAT-substituted complex yielded a structure built from open hydrogen-bonded sheets, and a significant fraction of the volume of the crystals (40%) proved to be available for the inclusion of guests. Weaker C−H···N and C−H···Br interactions were observed in the structures of the CN- and Br-substituted complexes, which yielded networks that were found to be more closely packed

CD Spectra of Polynuclear Complexes of Diimine Ligands: Theoretical and Experimental Evidence for the Importance of Internuclear Exciton Coupling

We have recently reported on dinuclear complexes Λ,Λ-[Co2L2Cl2]CoCl4 of two novel chiral ligands (1a and 1b) which contain pyridyl-imine chelate groups (Telfer, S. G.; Sato, T.; Kuroda, R. Chem. Commun. 2003, 1064−1065). The absolute configuration of the cobalt(II) centers was unambiguously assigned by X-ray crystallography. However, the sign of the exciton couplets in their CD spectra was opposite to that expected on the basis of the stereochemistry of the metal centers. We present a rationalization of these anomalous spectra in terms of an “internuclear” exciton coupling model which takes into account the coupling of chromophores located on different metal centers. We have performed a series of semiempirical (ZINDO) calculations which provide quantitative support to this model. These findings show that the absolute configuration of the metal centers in a polynuclear complex may be incorrectly assigned on the basis of CD data if internuclear coupling effects are not taken into consideration. We summarize the CD spectral data of number of other chiral polynuclear complexes from the literature, including dinuclear complexes bridged by the 2,2‘-bipyrimidine ligand, complexes of the HAT ligand, and dinuclear triple-stranded helicates. The amplitude of the CD spectra of many of these complexes is not additive with the number of chromophores. These anomalous spectra can be accounted for by taking internuclear coupling effects into consideration

Large Pore Isoreticular Strontium-Organic Frameworks: Syntheses, Crystal Structures, and Thermal and Luminescent Properties

Two isoreticular and topologically unique metal–organic frameworks (MOFs) have been synthesized using Sr­(NO3)2 and the organic linkers 2-nitro-[1,1′-biphenyl]-4,4′-dicarboxylic acid (H2bpdcNO2) and 2,2′-dinitro-[1,1′-biphenyl]-4,4′-dicarboxylic acid (H2bpdc­(NO2)2). The structures of [Sr­(bpdcNO2)2(DMF)2(H2O)2] (WUF-15; WUF = Wollongong University Framework) and [Sr4(bpdc­(NO2)2)4(DMF)2(H2O)4·2DMF] (WUF-16) were determined by single crystal X-ray diffraction (SCXRD) and are composed of infinite strontium carboxylate SBUs and contain large square (∼18 Å) and smaller triangular channels (∼9 Å) orientated parallel to each other and lined with nitro functional groups. An in situ ligand transformation of H2bpdc­(NO2)2 to benzo­[c]­cinnoline-3,8-dicarboxylic acid (H2bc) and formation of a nonporous coordination polymer of formula [Sr­(bc)­(H2O)2] (WUF-17) with interesting photoluminescent properties was discovered. Independent synthesis of H2bc enabled the preparation of WUF-17 crystals suitable for SCXRD structure determination. Powder X-ray diffraction and thermal and elemental analyses support the structures of all complexes

Multipurpose Metal–Organic Framework for the Adsorption of Acetylene: Ethylene Purification and Carbon Dioxide Removal

The separation of acetylene, ethylene, and carbon dioxide is a great challenge in view of their similar sizes and physical properties. Recently, adsorptive separations using porous metal–organic frameworks have risen to prominence. Here, we report a novel microporous metal–organic framework, termed MUF-17, that selectively adsorbs acetylene in the presence of ethylene or carbon dioxide. MUF-17 possesses one-dimensional zig-zag pores that are lined with amino and carboxylate groups, and coordinated water molecules. This pore surface is highly polar and has appropriate dimensions to interact optimally with guest acetylene molecules. Dispersion-corrected density functional theory calculations confirm the strong interactions between the framework and acetylene and illustrate the electrostatic basis for its lower affinity for other gases. The application of MUF-17 to gas separations was demonstrated by dynamic breakthrough measurements. It is a multipurpose adsorbent, removing trace quantities of acetylene from ethylene and sequestering bulk quantities in the presence of carbon dioxide. Its excellent performance fruitfully couples high selectivity with uptake capacity. Advantageously, MUF-17 is straightforward, robust, and inexpensive to prepare. Its recyclability and high stability render it a high-performance material for sustainable and energy-efficient separation processes

CD Spectra of Polynuclear Complexes of Diimine Ligands: Theoretical and Experimental Evidence for the Importance of Internuclear Exciton Coupling

We have recently reported on dinuclear complexes Λ,Λ-[Co2L2Cl2]CoCl4 of two novel chiral ligands (1a and 1b) which contain pyridyl-imine chelate groups (Telfer, S. G.; Sato, T.; Kuroda, R. Chem. Commun. 2003, 1064−1065). The absolute configuration of the cobalt(II) centers was unambiguously assigned by X-ray crystallography. However, the sign of the exciton couplets in their CD spectra was opposite to that expected on the basis of the stereochemistry of the metal centers. We present a rationalization of these anomalous spectra in terms of an “internuclear” exciton coupling model which takes into account the coupling of chromophores located on different metal centers. We have performed a series of semiempirical (ZINDO) calculations which provide quantitative support to this model. These findings show that the absolute configuration of the metal centers in a polynuclear complex may be incorrectly assigned on the basis of CD data if internuclear coupling effects are not taken into consideration. We summarize the CD spectral data of number of other chiral polynuclear complexes from the literature, including dinuclear complexes bridged by the 2,2‘-bipyrimidine ligand, complexes of the HAT ligand, and dinuclear triple-stranded helicates. The amplitude of the CD spectra of many of these complexes is not additive with the number of chromophores. These anomalous spectra can be accounted for by taking internuclear coupling effects into consideration

Multipurpose Metal–Organic Framework for the Adsorption of Acetylene: Ethylene Purification and Carbon Dioxide Removal

The separation of acetylene, ethylene, and carbon dioxide is a great challenge in view of their similar sizes and physical properties. Recently, adsorptive separations using porous metal–organic frameworks have risen to prominence. Here, we report a novel microporous metal–organic framework, termed MUF-17, that selectively adsorbs acetylene in the presence of ethylene or carbon dioxide. MUF-17 possesses one-dimensional zig-zag pores that are lined with amino and carboxylate groups, and coordinated water molecules. This pore surface is highly polar and has appropriate dimensions to interact optimally with guest acetylene molecules. Dispersion-corrected density functional theory calculations confirm the strong interactions between the framework and acetylene and illustrate the electrostatic basis for its lower affinity for other gases. The application of MUF-17 to gas separations was demonstrated by dynamic breakthrough measurements. It is a multipurpose adsorbent, removing trace quantities of acetylene from ethylene and sequestering bulk quantities in the presence of carbon dioxide. Its excellent performance fruitfully couples high selectivity with uptake capacity. Advantageously, MUF-17 is straightforward, robust, and inexpensive to prepare. Its recyclability and high stability render it a high-performance material for sustainable and energy-efficient separation processes

Multipurpose Metal–Organic Framework for the Adsorption of Acetylene: Ethylene Purification and Carbon Dioxide Removal

The separation of acetylene, ethylene, and carbon dioxide is a great challenge in view of their similar sizes and physical properties. Recently, adsorptive separations using porous metal–organic frameworks have risen to prominence. Here, we report a novel microporous metal–organic framework, termed MUF-17, that selectively adsorbs acetylene in the presence of ethylene or carbon dioxide. MUF-17 possesses one-dimensional zig-zag pores that are lined with amino and carboxylate groups, and coordinated water molecules. This pore surface is highly polar and has appropriate dimensions to interact optimally with guest acetylene molecules. Dispersion-corrected density functional theory calculations confirm the strong interactions between the framework and acetylene and illustrate the electrostatic basis for its lower affinity for other gases. The application of MUF-17 to gas separations was demonstrated by dynamic breakthrough measurements. It is a multipurpose adsorbent, removing trace quantities of acetylene from ethylene and sequestering bulk quantities in the presence of carbon dioxide. Its excellent performance fruitfully couples high selectivity with uptake capacity. Advantageously, MUF-17 is straightforward, robust, and inexpensive to prepare. Its recyclability and high stability render it a high-performance material for sustainable and energy-efficient separation processes

Metal–Organic Framework Nanocrystals as Sacrificial Templates for Hollow and Exceptionally Porous Titania and Composite Materials

We report a strategy that employs metal–organic framework (MOF) crystals in two roles for the fabrication of hollow nanomaterials. In the first role the MOF crystals provide a template on which a shell of material can be deposited. Etching of the MOF produces a hollow structure with a predetermined size and morphology. In combination with this strategy, the MOF crystals, including guest molecules in their pores, can provide the components of a secondary material that is deposited inside the initially formed shell. We used this approach to develop a straightforward and reproducible method for constructing well-defined, nonspherical hollow and exceptionally porous titania and titania-based composite nanomaterials. Uniform hollow nanostructures of amorphous titania, which assume the cubic or polyhedral shape of the original template, are delivered using nano- and microsized ZIF-8 and ZIF-67 crystal templates. These materials exhibit outstanding textural properties including hierarchical pore structures and BET surface areas of up to 800 m²/g. As a proof of principle, we further demonstrate that metal nanoparticles such as Pt nanoparticles, can be encapsulated into the TiO₂ shell during the digestion process and used for subsequent heterogeneous catalysis. In addition, we show that the core components of the ZIF nanocrystals, along with their adsorbed guests, can be used as precursors for the formation of secondary materials, following their thermal decomposition, to produce hollow and porous metal sulfide/titania or metal oxide/titania composite nanostructures