Crystalline molecular alloys

Ballesteros, B., Coco, S. and Espinet, P. (2004) Mesomorphic Mixtures of Metal Isocyanide Complexes, Induding Smectic C Mesophases at room temperature and Liquid Crystalline Molecular Alloys . Chemistry of Materials, 16, 2062-2067. 

Figure 4.26 (a) Epitaxial growth occurs by one crystal growing on the surface of another, isostructural one. (b) Co(CN) and Fe(CN) salts of an organic dication can be epitaxially grown.S. Ferlay and M. W. Hossieni, Crystalline molecular alloys, Chem. Common., 2004, 788-789. Reproduced by permission of The Royal Society of Chemistry. 

Ferlay, S. and Hossieni, M. W., Crystalline molecular alloys, Chem. Commun., 2004, 788-789. 

With the use of epitaxial growth methods such as molecular beam epitaxy (MBE) or metal organic vapor deposition (MOCVD), it is possible to grow single crystalline ternary alloy systems such as AljrGai j As or quaternary systems such as Ga lhi xAsyPi y with controlled composition as well as to form heterostructures by growing one compound semiconductor epitaxially on top of another compound semiconductor. (Epitaxy means that the lattice periodicity is maintained across the growth interface.)... 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

Amorphous (rapidly quenched) metals and alloys have been investigated as catalysts (Schlogl, 1985). It has been found that adsorption characteristics of carbon monoxide on metallic glasses are different from those on crystalline materials. For example CO is found to dissociate readily on the surface of Ni76Bi2Si,2 metglass, but it is always molecularly adsorbed on metallic nickel (Prabhakaran Rao, 1985). 

Each pure element forms a crystalline solid when it freezes. In these crystals, the atoms of the elements are stacked in regular arrays that form a pattern characteristic of the particular element. Molecular compounds (such as carbon dioxide, water, and glucose) and metal alloys (such as brass) are also crystalline. Ionic compounds (such as sodium chloride and... 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

In this entry, the principal chemical features of defect populations (defect chemistry) will be described from the restricted viewpoint of crystalline inorganic solids. The influence of defects upon mechanical properties will be excluded and defects that may have greatest relevance to physical properties will be treated from the point of view of chemical importance. Defects in molecular crystals and amorphous and glassy solids will be omitted see Noncrystalline Solids), as will the important areas of alloys see Alloys), thin films see Thin Film Synthesis of Solids), and carbon nanotubes and related nanoparticles see Carbon Fullerenes). References to the literature before 1994 are to be found in the corresponding article in the first edition of this Encyclopedia. ... 

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