Soft crystals, description

The detailed descriptions of the structures of calamitic phases allow us to classify the mesomorphic liquid crystal state, and to place this state in context with the crystalline and amorphous liquid states [3]. Table 1 describes the relationship between ordered crystals, disordered or soft crystals, liquid crystals and the isotropic liquid. 

The molecular packing of MOMs results from a precise and subtle balance of several intermolecular interactions within a narrow cohesion energy range of less than 1 eV molec . This is the reason why crystal engineering is so powerful because this balance can be intentionally modified but at the same time it implies that MOMs are soft materials and that polymorphism is favoured. Detailed descriptions on the fundamentals of interatomic and intermolecular interactions can be found in many books (see e.g., Kitaigorodskii, 1961). Here we briefly describe the relevant interactions for MOMs and give a new approach supported on the nanoscience perspective. 

An isolated CS plane is referred to as a Wadsley defect and a random array of CS planes is considered to constitute planar (extended) defects which are entirely different from point defects. It is obvious that when CS planes occur at regular intervals, the composition of the crystal is stoichiometric, whereas a random array of CS planes results in nonstoichiometric compositions. While we have invoked anion vacancies which are later annihilated in our description of CS plane formation, we must point out that vacancies are not essential precursors for the formation of CS planes. Accommodating anion-deficient nonstoichiometry through CS mechanism is a special feature restricted to d° metal oxides such as W03, Nb205 and TiOz which exhibit soft phonon modes. Soft phonon modes in metal oxides arise from soft metal-orxygen potentials which permit large cation relaxation. The latter... 

Reaction of lithium diphenylphosphide with 1,2-dibromodifluoroethylene in THF results in displacement of bromines rather than fluorine, presumably an illustration of the softness of the base PhaP- the resulting solid ciiS-ligand PhaP CFrCF-PPhs, which separated from the oily tra j-isomer, was used to prepare a number of palladiumfu) complexes.Further descriptions of the displacement of olefinic chlorine by phosphorus, using phosphites as nucleophiles, in polyfluorocycloalkenes (see Vol. 2, pp. 68 and 246) have appeared,and the crystal structure of hexafluoro(triphenylphosphoranylidene)cyclobutene, the product of hexafluorocyclobutene and triphenylphosphine (see p. 257) has been determined. ... 

Classical Descriptions of Inclusion Compounds, p. 253 Clathrate Hydrates, p. 274 Concepts in Crystal Engineering, p. 319 Crown Ethers, p. 326 Cryptands, p. 334 DNA Nanotechnology, p. 475 Enzyme Mimics, p. 546 The Lock and Key Principle, p. 809 Molecular-level Machines, p. 931 Selectivity Thermodynamic and Kinetic, p. 1225 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly Terminology, p. 1263 Soft and Smart Materials, p. 1302 Spherands, p. 1344... 

The following is restricted to membrane phases. However, the description is general enough that it stands for soft matter systems that possess internal disorder (liquid crystals, colloids, polymers, plastic crystals, etc.)... 

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