The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Reduced transition metal colloids: a novel family of reusable catalysts

2.3. Amorphous Minerals 4354 3. Biological Routes to Controlling Morphology 4354 3.1. General Mechanisms 4356 3.1.1. Soluble and Insoluble Organic Molecules 4356 3.1.2. Control over Crystal Polymorph 4357 3.1.3. Control over Crystal Orientation 4359 3.2. Single-Crystal Biominerals 4359 3.2.1. Organic and Inorganic Soluble Additives 4360 3.2.2. Templating of Single-Crystal Morphologies 4361 3.3. Polycrystalline Biominerals 4366 3.3.1. Nacre Formation in Mollusks 4366 3.3.2. ForaminiferasA Biogenic Mesocrystal 4368 3.4. Amorphous Biominerals 4370 3.4.1. Silicification in Diatoms 4370 3.4.2. In Vitro Studies of Silicification in Diatoms 4371 4. Bioinspired Routes to Controlling Crystal Morphologies 4371

Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems

Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

/pdf/hierarchically-porous-materials-synthesis-strategies-and-568soqnq77.pdf

Hierarchically porous materials: synthesis strategies and structure design

Reduction of the five-coordinate iron(II) dihalide complexes (iPrPDI)FeX2 (iPrPDI = ((2,6-CHMe2)2C6H3NCMe)2C5H3N; X = Cl, Br) with sodium amalgam under 1 atm of dinitrogen afforded the square pyramidal, high spin iron(0) bis(dinitrogen) complex (iPrPDI)Fe(N2)2. In solution, (iPrPDI)Fe(N2)2 loses 1 equiv of N2 to afford the mono(dinitrogen) adduct (iPrPDI)Fe(N2). Both dinitrogen compounds serve as effective precatalysts for the hydrogenation and hydrosilation of olefins and alkynes. Effecient catalytic reactions are observed with low catalyst loadings (≤0.3 mol %) at ambient temperature in nonpolar media. The catalytic hydrosilations are selective in forming the anti-Markovnikov product. Structural characterization of a high spin iron(0) alkyne and a bis(silane) σ-complex has also been accomplished and in combination with isotopic labeling studies provides insight into the mechanism of both catalytic C−H and catalytic C−Si bond formation.

Preparation and molecular and electronic structures of iron(0) dinitrogen and silane complexes and their application to catalytic hydrogenation and hydrosilation.

Exact replication of biological structures by chemical vapor deposition of silica.

Metal atoms, easily formed by vaporizing metals at high temperatures under vacuum, are reacted with inorganic and organic compounds in solution at 80 to 273°K or by co-condensing the atoms and substrate vapors at 10 to 80°K. Gram quantities of products containing metals in low valency states can be isolated in many cases, and some of the compounds formed are inaccessible by conventional synthetic routes.

Synthetic Reactions of Metal Atoms at Temperatures of 10 to 273°K†

The matrix infrared spectrum of PN and SiS

Publisher Summary This chapter discusses the fundamentals of metal–atom synthesis and its experimental methods. Metal atoms can be formed by thermally vaporizing metals under vacuum. The enhanced reactivity of metal atoms compared with bulk metals is partly due to the endothermicity of the atoms and partly due to kinetic factors. The desired atom–molecule reaction will compete only if there is a large excess of the organic molecules; atom–molecule ratios of 1:10 to 1:50 are commonly used to obtain acceptable yields of organometallic products based on the metal vapor condensed. Simple alkanes are generally unreactive toward metal atoms at low temperature. All the methods used for evaporating metals for atom synthesis had been developed originally for the deposition of thin metal films. The interaction of metal atoms with monoalkenes has been investigated on both a spectroscopic and preparative scale. Alkynes have not yielded isolable organometallic complexes in their reactions with metal atoms. A number of new metal–dinitrogen complexes of type M(N2)n have been detected in the reaction of metal atoms with N2 under matrix isolation conditions. The catalytic oligomerization of butadiene is found to occur in most transition metal vapor–butadiene reactions. The interaction of metal atoms with cyclopentadiene is characterized by a tendency toward the formation of a stable electronic configuration for the metal. Reactions of cobalt and nickel atoms with toluene and other arenes yield condensates in which the metal is in a very reactive state. When metal atoms condense on a surface, the recombination to form bulk metal will occur at a rate controlled only by diffusion even at 4 K.

Peter L. Timms

Papers

Exact replication of biological structures by chemical vapor deposition of silica.

Synthetic Reactions of Metal Atoms at Temperatures of 10 to 273°K†

The matrix infrared spectrum of PN and SiS

Metal Atom Synthesis of Organometallic Compounds

Preparation and structure of cis-[Pt(BF2)2(PPh3)2]: the first crystallographically characterised complex containing the BF2 ligand