Frameworks, bridged

Fig. 2. Idealized deltahedra and deltahedral fragments for closo, nido and arachno boranes and heteroboranes. From left to right the vertical columns give generic closo, nido, and arachno frameworks bridge hydrogens and BH2 groups are not shown, but when appropriate they are placed around the open...

Ru3(CO)i2] and 7,8-Me2-Kfatoms with the open CBBBlf or CCBBB faces, respectively, coordinated in a pentahapto fashion to one metal atom while the carborane cage forms two exo-polyhedral B-H M bonds with the other two metal atoms. 

Corma A, Iglesias M, Llabres i Xamena EX, Sanchez F. Cu and Au metal-organic frameworks bridge the gap between homogeneous and heterogeneous catalysts for alkene cyclo-propanation reactions. Chem Eur J 2010 16 9789-95. 

Buckminster Fuller was the inventor of self-supporting polygon frameworks, e.g., of pavilions. Synonyms (root)ballene, buckminsterfullerenc( BF ), carbosoccer, soo r(ball)ene, spherene. The proposed bridged-fused ring system and von-Baeyer names and numberings vary. 

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

A rare-earth-exchanged zeolite increases hydrogen transfer reactions. In simple terms, rare earth forms bridges between two to three acid sites in the catalyst framework. In doing so, the rare earth protects... 

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