From molecules to extended solids

Come on in Take a look at the chemical portraits in the galleries that follow. 

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Whereas the electronic structure of atoms, molecules, and extended solids is quite well explored from both experimental and theoretical viewpoint, little is known about the systematic development of the electronic structure as single atoms are combined to form clusters and eventually solids. 

From a synthetic point of view, much of the appeal of MOFs and CPs lies in the potential for these materials to be viewed as targets of reactions (6). The use of metal centers with appropriately paired organic molecules wherein the local coordination geometry preferences of the metal center are exploited lets one think in terms of assembling higher dimensional solids. This finding is in stark contrast to earlier, high-temperature approaches to extended solid-state structures. Indeed, the vast majority of MOF and CP materials have been synthesized at room temperature, or at most under solvothermal conditions. 

In a complementary approach, the electronic structures of molecules and extended solids can be built up from constituent atoms with use of molecular orbital theory. The orbitals evolve into bands which provide a useful description when the number of atoms is large. To illustrate, consider the interaction of the orbitals in a row of carbon atoms as the number of carbon sites N varies from small to very large (Figure 2). For N=2, bonding and antibonding... 

The theory described above has been applied to a great variety of materials, thus demonstrating the feasibility of calculations of that kind. They include the elemental semiconductors [159], III-V [163] and II-VI compounds [164], ionic crystals like MgO [165], CaO [166], NiO [167], alkali halides [168], Ti02 (with a sizeable amount of covalency) [169], rare-gas crystals [170,171], solid mercury [172,173] and the rar earth compound GdN [174] with the 4/ electrons kept within the core. The method of increments allows the CCSD local correlation scheme to be extended from molecules to solids. In most cases the program package CRYSTAL [23] was used for the SCF part including a localization procedure for determining the Wannier functions. 

A more detailed treatment has been given by Gurfein and his associates who chose as their pore model a cylinder with walls only one molecule thick. A few years later, Everett and Fowl extended the range of models to include not only a slit-shaped pore with walls one molecule thick, but also a cylinder tunnelled from an infinite slab of solid and a slit formed from parallel slabs of solid. 

Since the compartmentalization occurs as a result of microphase separation of an amphiphilic polyelectrolyte in aqueous solution, an aqueous system is the only possible object of study. This limitation is a disadvantage from a practical point of view. Our recent studies, however, have shown that this disadvantage can be overcome with a molecular composite of an amphiphilic polyelectrolyte with a surfactant molecule [129], This composite was dissolvable in organic solvents and dopable in polymer film, and the microphase structure was found to remain unchaged in the composite. This finding is important, because it has made it possible to extend the study on photo-systems involving the chromophore compartmentalization to organic solutions and polymer solid systems. 

According to the U.S. National Nanotechnology Institute, nanotechnology encompasses research and development to synthesize, control, and manipulate stmctures, devices, and systems of novel properties and functions because of their size at the atomic, molecular, or macromolecular levels in the length scale ranging from approximately 1 to 100 nanometers. Indeed, this length scale is of particular relevance to heterogeneous catalysis, where the active sites are small crystallites or domains of the active phase. The reaction typically involves atom-molecule interactions, and the active sites are placed in or on an extended solid where the access paths to the active sites are tens to hundreds of nanometers. The issue of access path is a familiar territory in... 

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