Polymolecularity, defined

One point to address concerns the use of the words s pramolecular and supermolecule. The concept of supramolecular chemistry has become a unifying attractor, in which areas that have developed independently have spontaneously found their place. The word supramolecular has been used in particular for large multiprotein architectures and organized molecular assemblies [1.16]. On the other hand, in theoretical chemistry, the computational procedure that treats molecular associations such as the water dimer as a single entity is termed the supermolecule approach [1.34,1.35]. Taking into account the existence and the independent uses of these two words, one may then propose that supramolecular chemistry be the broader term, concerning the chemistry of all types of supramolecular entities from the well-defined supermolecules to extended, more or less organized, polymolecular associations. The term super molecular chemistry would be restricted to the specific chemistry of the supermolecules themselves. 

Dynamic features of supermolecules correspond on the intermolecular level to the internal conformational motions present in molecules themselves and define molecular recognition processes by their dynamics in addition to their structural aspects. They add a further important facet to the behaviour of these species and may influence their functional features in reactions and transport processes as well as in polymolecular assemblies. 

As pointed out in Chapter 1, supramolecular chemistry comprises two broad, partially overlapping areas covering on the one hand the oligomolecular supermolecules and, on the other, the supramolecular assemblies, extended polymolecular arrays presenting a more or less well-defined microscopic organisation and macroscopic features depending on their nature (layers, films, membranes, vesicles, micelles, microemulsions, gels, mesomorphic phases, solid state species, etc.). 

There are two types of objects in supramolecular chemistry supermolecules (i.e., well-defined discrete oligomolecular species that result from the inter-molecular association of a few components), and supramolecular arrays (i.e., polymolecular entities that result from the spontaneous association of a large, undefined number of components) (4, 5). Both are observed in some metal-xanthate structures to be described herein. The most frequent intermolecular forces leading to self-assembly in metal xanthates are so-called secondary bonds . The secondary bond concept has been introduced by Nathaniel W. Alcock to describe interactions between molecules that result in interatomic distances longer than covalent bonds and shorter than the sum of van der Waals radii (6). Secondary bonds [sometimes called soft-soft interactions (7)] are typical for heavier p-block elements and play an important role as bonding motifs in supramolecular organometallic chemistry (8). Other types of intermolecular forces (e.g., Ji- -ji stacking) are also observed in the crystal structures of metal xanthates. 

There are two types of subjects in supramolecular chemistry (a) the supramolecular assemblies or systems, also called supramolecular arrays, that is, polymolecular entities that resultfrom the spontaneous association of a large undefined number of components, and (b) supermolecules, that is, well-defined discrete oligomolecular species that result from the intermolecular association of a few components... 

Increased functionality of the organometallic moiety will lead to more intricate supramolecular assemblies. A suggestive organometallic example is provided by tetra(p-cyanophenyl)silane, Si(C6H4CN-p)4, which forms a three-dimensional self -organized supramolecular network of interpenetrating double layers by coordination with silver ions [27] and a layered supramolecular structure with TiCU [28], both imposed by the directionality of tetrahedral silicon centers. Supramolecular assemblies are defined as "extended polymolecular arrays presenting a more or less... 

Due to the natural polymolecularity of any polymer sample, the system P-I-LMWL should be regarded as a polynary one, containing (stability boundary of the single-pheise system state is a spinodal surface in the (i/-t-1 )-dimensional space based on the j/ -dimensional polyhedron of composition (with the material balance taken into account) and the temperature axis, the critical state being defined by a i -dimensional surface. 

Supramolecular assembly Polymolecular entities that result from the association of a large, undefined number of molecular entities into a specific phase having a definable organization., e.g. micelles, vesicles etc. 

The highly selective processes of molecular recognition are, of course, of stereochemical nature. Thus may be defined a supramolecular stereochemistry that extends from supermolecules to polymolecular assemblies. Different spatial dispositions of the components of a supermolecule with respect to each other lead to supramolecular stereoisomers. Their eventual interconversion will depend on the properties of the interactions that hold them together, i.e. on the variation of the intermolecular interaction energy with distances and angles. There is thus an intermolecular conformational analysis like there is an intramolecular one. 

Supramolecular chemistry opens up new perspectives in materials chemistry towards an area of supramolecular engineerings which gives access to the molecular-information-controlled generation of well-defined polymolecular architectures and patterns in molecular assemblies, layers, films, membranes, micelles, gels, mesophases and solids as well as in large inorganic entities, polymetallic coordination architectures and coordination polymers. 

Star-shaped polymers have gained increasing interest because of their compact structure and high segment density, and because very efficient synthetic methods have made possible the functionalization of the outer branch ends. Until recently, anionic polymerization was one of the best methods to obtain well-defined star-shaped polymers of predetermined branch molar mass. This technique provided the long lifetime for the active sites necessary to allow the formation of star-shaped macromolecules. Anionic polymerization also limited the polymolecularity of the samples. Given the appropriate reaction conditions, the functionality of the core can be controlled in advance. 

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