Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

The Chemistry and Applications of Metal-Organic Frameworks

J. Appl. Cryst.の発刊に際して

A critical review of the emerging field of MOF-based catalysis is presented. Discussed are examples of: (a) opportunistic catalysis with metal nodes, (b) designed catalysis with framework nodes, (c) catalysis by homogeneous catalysts incorporated as framework struts, (d) catalysis by MOF-encapsulated molecular species, (e) catalysis by metal-free organic struts or cavity modifiers, and (f) catalysis by MOF-encapsulated clusters (66 references).

Metal–organic framework materials as catalysts

1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

2.2. MOFs with Metal Active Sites 4614 2.2.1. Early Studies 4614 2.2.2. Hydrogenation Reactions 4618 2.2.3. Oxidation of Organic Substrates 4620 2.2.4. CO Oxidation to CO2 4626 2.2.5. Phototocatalysis by MOFs 4627 2.2.6. Carbonyl Cyanosilylation 4630 2.2.7. Hydrodesulfurization 4631 2.2.8. Other Reactions 4632 2.3. MOFs with Reactive Functional Groups 4634 2.4. MOFs as Host Matrices or Nanometric Reaction Cavities 4636

Engineering Metal Organic Frameworks for Heterogeneous Catalysis

Metalloporphyrins are exceedingly useful building blocks for the design and synthesis of molecularly based solids. The use of hydrogen bonding or metal ion coordination provides a wide range of framework solids. Using various polyfunctionalized porphyrins, we have created porous solids that are thermally robust and that retain their internal porosity upon loss of solvates. Their pore dimensions are comparable to zeolites, and they show shape and size selectivity in sorption of guest molecules and in epoxidation of alkenes.

Microporous Porphyrin Solids

A new class of sterically hindered dendrimer-metalloporphyrins was synthesized for use as shape-selective oxidation catalysts. A series of oxidatively robust poly(phenylesters) dendrimers were prepared through a convergent synthesis. Monodendrons were appended to the meta-positions of the 5,10,15,20-tetrakis(3‘,5‘-hydroxyphenyl)porphinatomanganese(III) chloride to obtain a sterically protected metal center. These complexes have been examined as regioselective oxidation catalysts for both intra- and intermolecular cases. Epoxidation of nonconjugated dienes and alkene mixtures of 1-alkene and cyclooctene catalyzed by dendrimer-metalloporphyrins has been carried out using iodosylbenzene as the oxygen donor. Significantly greater regioselectivity is observed with the dendrimer-metalloporphyrins, relative to the corresponding parent, 5,10,15,20-tetraphenylporphyrinatomanganese(III) cation. To examine the extent of steric crowding around the porphyrin from the dendrimers, molecular modeling studies were perform...

Dendrimer-metalloporphyrins: Synthesis and catalysis

The free-base octabromotetraphenylporphyrin (H2OBP) has been prepared by a novel bromination reaction of (meso-tetraphenylporphyrinato)copper(II). The metal [V(IV)O, Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Ag(II), Pt(II)] derivatives exhibit interesting electronic spectral features and electrochemical redox properties. The electron-withdrawing bromine substituents at the pyrrole carbons in H2OBP and M(OBP) derivatives produce remarkable red shifts in the Soret (50 nm) and visible bands (100 nm) of the porphyrin. The low magnitude of protonation constants (pK3 = 2.6 and pK4 = 1.75) and the large red-shifted Soret and visible absorption bands make the octabromoporphyrin unique. The effect of electronegative bromine substituents at the peripheral positions of the porphyrin has been quantitatively analyzed by using the four-orbital approach of Gouterman. A comparison of MO parameters of MOBP derivatives with those of the meso-substituted tetraphenylporphyrin (M(TPP)) and unsubstituted porphine (M(P)) derivatives provides an explanation for the unusual spectral features. The configuration interaction matrix element of the M(OBP) derivatives is found to be the lowest among the known substituted porphyrins, indicating delocalization of ring charge caused by the increase in conjugation of p orbitals of the bromine onto the ring orbitals. The electron-transfer reactivities of the porphyrins have been dramatically altered by the peripheral bromine substituents, producing large anodic shifts in the ring and metal-centered redox potentials. The increase in anodic shift in the reduction potential of M(OBP)s relative to M(TPP)s is found to be large (550 mV) compared to the shift in the oxidation potential (300 mV). These shifts are interpreted in terms of the resonance and inductive interactions of the bromine substituents.

Octabromotetraphenylporphyrin and its metal derivatives: Electronic structure and electrochemical properties

Symmetrically substituted octahydroxy porphyrins, tetrakis(3',5'-dihydroxyphenyl)porphyrin, H2T(3',5'- DHP)P, tetrakis(2',6'-dihydroxyphenyl)porphyrin, H2T(2',6'-DHP)P, and their Zn(II) and Mn(III) derivatives have been developed as building blocks for supramolecular hydrogen-bonded networks. The crystal structures of a series of these porphyrins exhibit unique structural features through assembly of porphyrin networks by means of directional hydrogen bonding. The position of the peripheral hydroxyl groups, the choice of metallo- or free base porphyrin, and the nature of the solvate (i.e., guest) dramatically influence structural features. A one-dimensional, columnar structure is found for H2T(3',5'-DHP)P‚5EtOAc. With benzonitrile as solvate, the structure of H2T(3',5'-DHP)P‚7C6H5- CN changes substantially to a three-dimensional corrugated-sheet structure in order to accommodate a larger pore size. When the hydroxyl substituents are simply changed from the m- to the o-phenyl positions, an essentially two-dimensional layered structure is formed for H2T(2',6'-DHP)P‚4EtOAc. Zn(T(2',6'-DHP)P)(EtOAc)2‚2EtOAc has a two-dimensional layered structure, similar to that of its free base H 2T(2',6'-DHP)P interaction between the aryl rings of the adjacent layers. The crystal structures of both Zn(T(3 ',5'-DHP)P) and Mn(T(3',5'-DHP)P)(Cl) exhibited three-dimensional hydrogen-bonding features. Zn(T(3',5'-DHP)P)(THF)2‚2THF‚3CH2Cl2 has a three-dimensional interconnected layered structure with metalloporphyrins arranged in a slipped stack orientation within the layers. In the structure of Mn(T(3',5'-DHP)P)(THF)2‚Cl‚2THF‚5C6H5CH3, a chloride anion dictates the three-dimensional packing by bridging four metalloporphyrin molecules through Cl‚‚‚HO bonding interactions. In all of these structures, large solvate-filled channels are present with cross-sections as large as 42 A 2 . The pore volumes of these channels are exceptionally large: as much as 67% of the unit cell volume.

Hydrogen-Bonded Porphyrinic Solids: Supramolecular Networks of Octahydroxy Porphyrins

Synthetic methods are reported for the isolation of a number of buckministerfulleride(1-) salts. Counterions include cobaltocenium ion, Na(dibenzo-18-crown-6)[sup +], and bis(N-methylimidazole)(tetraphenylporphinato)tin(IV[sup 2+]). The EPR spectrum of C[sub 60][sup [minus]] in frozen solution shows two unusual features. First, there is a counterion-dependent anisotropy observed at low temperatures. This is ascribed to an ellipsoidal distortion induced by ion pairing. It is consistent with, but not directly ascribable to, a static Jahn-Teller distortion. Second, there are two components to the high-temperature spectrum; the broad essentially isotropic, major signal and a narrower [open quotes]spike[close quotes]. The narrower signal is ascribed to thermal population of a low-lying excited state, a natural consequence of the distortion that splits the [sup 2]T[sub 1u] state into closely spaced [sup 2]E and [sup 2]A states. In contrast to intuition and to ab initio calculations, the [sup 2]E state is lowest in most systems studied to date. 43 refs., 4 figs.

Puttaiah Bhyrappa

Papers

Microporous Porphyrin Solids

Dendrimer-metalloporphyrins: Synthesis and catalysis

Octabromotetraphenylporphyrin and its metal derivatives: Electronic structure and electrochemical properties

Hydrogen-Bonded Porphyrinic Solids: Supramolecular Networks of Octahydroxy Porphyrins

Buckminsterfulleride(1-) salts : synthesis, EPR, and the Jahn-Teller distortion of C60-