Fernando J. Uribe-Romo

Exceptional chemical and thermal stability of zeolitic imidazolate frameworks

Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m2/g), high thermal stability (up to 550°C), and remarkable chemical resistance to boiling alkaline water and organic solvents.

A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework

A new crystalline porous three-dimensional covalent organic framework, termed COF-300, has been synthesized and structurally characterized. Tetrahedral tetra-(4-anilyl)-methane and linear terephthaldehyde building blocks were condensed to form imine linkages in a material whose X-ray crystal structure shows five independent diamond frameworks. Despite the interpenetration, the structure has pores of 7.2 A diameter. Thus, COF-300 shows thermal stability up to 490 degrees C and permanent porosity with a surface area of 1360 m(2) g(-1).

Crystalline Covalent Organic Frameworks with Hydrazone Linkages

Condensation of 2,5-diethoxyterephthalohydrazide with 1,3,5-triformylbenzene or 1,3,5-tris(4-formylphenyl)benzene yields two new covalent organic frameworks, COF-42 and COF-43, in which the organic building units are linked through hydrazone bonds to form extended two-dimensional porous frameworks. Both materials are highly crystalline, display excellent chemical and thermal stability, and are permanently porous. These new COFs expand the scope of possibilities for this emerging class of porous materials.

Lattice Expansion of Highly Oriented 2D Phthalocyanine Covalent Organic Framework Films

Expanding into application: covalent organic framework (COF) films are ideally suited for vertical charge transport and serve as precursors of ordered heterojunctions. Their pores, however, were previously too small to accommodate continuous networks of complementary electron acceptors. Four phthalocyanine COFs with increased pore size well into the mesoporous regime are now described.

Porous, conductive metal-triazolates and their structural elucidation by the charge-flipping method.

A new family of porous crystals was prepared by combining 1H-1,2,3-triazole and divalent metal ions (Mg, Mn, Fe, Co, Cu, and Zn) to give six isostructural metal-triazolates (termed MET-1 to 6). These materials are prepared as microcrystalline powders, which give intense X-ray diffraction lines. Without previous knowledge of the expected structure, it was possible to apply the newly developed charge-flipping method to solve the complex crystal structure of METs: all the metal ions are octahedrally coordinated to the nitrogen atoms of triazolate such that five metal centers are joined through bridging triazolate ions to form super-tetrahedral units that lie at the vertexes of a diamond-type structure. The variation in the size of metal ions across the series provides for precise control of pore apertures to a fraction of an Angstrom in the range 4.5 to 6.1 Å. MET frameworks have permanent porosity and display surface areas as high as some of the most porous zeolites, with one member of this family, MET-3, exhibiting significant electrical conductivity.

Ring-Opening Reactions within Porous Metal―Organic Frameworks

Two new metal-organic framework (MOF) structures, IRMOF-3b and -3c, were prepared by ring-opening reaction of 1,3-propanesultone and 2-methylaziridine with an amine functionalized MOF, IRMOF-3. The new structures are permanently functionalized with covalently linked sulfonate and alkyamine units, respectively. The underlying framework structure is retained after reaction as confirmed by powder X-ray diffraction. The high porosity of IRMOF-3 is also maintained, as evidenced by nitrogen adsorption experiments, which yield Brunauer-Emmett-Teller (BET) surface areas of 1380 and 530 m(2) g(-1) compared to 2040 m(2) g(-1) in the parent material. Ring-opening reactions provide a versatile route to irreversible binding of a range of functionalities that are otherwise difficult to access in MOFs.

Mechanically Shaped Two-Dimensional Covalent Organic Frameworks Reveal Crystallographic Alignment and Fast Li-Ion Conductivity

Covalent organic frameworks (COFs) usually crystallize as insoluble powders, and their processing for suitable devices is thought to be limited. We demonstrate that COFs can be mechanically pressed into shaped objects having anisotropic ordering with preferred orientation between hk0 and 00l crystallographic planes. Five COFs with different functionality and symmetry exhibited similar crystallographic behavior and remarkable stability, indicating the generality of this processing. Pellets prepared from bulk COF powders impregnated with LiClO4 displayed room temperature conductivity up to 0.26 mS cm(-1) and high electrochemical stability. This outcome portends use of COFs as solid-state electrolytes in batteries.

Accessing extended and partially fused hexabenzocoronenes using a benzannulation–cyclodehydrogenation approach

A rapid and efficient approach to prepare extended or partially fused hexabenzocoronene derivatives is described. The method is based on the sequential benzannulation and cyclodehydrogenation (Scholl oxidation) of simple diaryl alkynes. The benzannulation reaction proceeds efficiently on highly congested substrates and with complete regioselectivity. Scholl oxidation of the resulting oligo(arylene)s proceeds without rearrangements and provides either fully fused or specific partially fused polycyclic aromatic hydrocarbon products. The partially fused derivatives are a new class of contorted aromatic systems with high solubility, enhanced visible absorption, and reversible redox processes. The efficiency and specificity of the benzannulation and oxidation reactions are promising for accessing new classes of organic semiconductors and carbon nanostructures.

Ambipolar Transport in Solution-Synthesized Graphene Nanoribbons

Graphene nanoribbons (GNRs) with robust electronic band gaps are promising candidate materials for nanometer-scale electronic circuits. Realizing their full potential, however, will depend on the ability to access GNRs with prescribed widths and edge structures and an understanding of their fundamental electronic properties. We report field-effect devices exhibiting ambipolar transport in accumulation mode composed of solution-synthesized GNRs with straight armchair edges. Temperature-dependent electrical measurements specify thermally activated charge transport, which we attribute to inter-ribbon hopping. With access to structurally precise materials in practical quantities and by overcoming processing difficulties in making electrical contacts to these materials, we have demonstrated critical steps toward nanoelectric devices based on solution-synthesized GNRs.

Systematic variation of the optical bandgap in titanium based isoreticular metal–organic frameworks for photocatalytic reduction of CO2 under blue light

A series of metal–organic frameworks isoreticular to MIL-125-NH2 were prepared, where the 2-amino-terephthalate organic links feature N-alkyl groups of increasing chain length (from methyl to heptyl) and varying connectivity (primary and secondary). The prepared materials display reduced optical bandgaps correlated with the inductive donor ability of the alkyl substituent as well as high photocatalytic activity towards the reduction of carbon dioxide under blue illumination operating over 120 h. Secondary N-alkyl substitution (isopropyl, cyclopentyl and cyclohexyl) exhibits larger apparent quantum yields than the primary N-alkyl analogs directly related to their longer lived excited-state lifetime. In particular, MIL-125-NHCyp (Cyp = cyclopentyl) exhibits a small bandgap (Eg = 2.30 eV), a long-lived excited-state (τ = 68.8 ns) and a larger apparent quantum yield (Φapp = 1.80%) compared to the parent MIL-125-NH2 (Eg = 2.56 eV, Φapp = 0.31%, τ = 12.8 ns), making it a promising candidate for the next generation of photocatalysts for solar fuel production based on earth-abundant elements.