Supramolecular cluster

This is a very new field, but given the current interest in both dendrimer chemistry and supramolecular chemistry, it is one that is likely to receive attention in the future. The prospect of preparing well-defined molecular assemblies, rather than ill-defined clusters, is attractive, and is expected to give access to new properties that can be controlled by the molecular architecture of the assembly. New and useful materials seem likely to emerge as this chemistry grows and is exploited in the years to come. 

The potential of the cluster units described here to participate in intermolecular chalcogen-chalcogen interactions combined with the easy modification of their outer coordination sphere with ligands of different nature, i.e., redox active, hydrogen donors, bi-functional, etc., make these systems useful blocks for the construction of supramolecular materials with multi-physical properties. 

The series Structure and Bonding publishes critical reviews on topics of research concerned with chemical structure and bonding. The scope of the series spans the entire Periodic Table and addresses structure and bonding issues associated with all of the elements. It also focuses attention on new and developing areas of modem structural and theoretical chemistry such as nanostructures, molecular electronics, designed molecular solids, surfaces, metal clusters and supramolecular structures. Physical and spectroscopic techniques used to determine, examine and model structures fall within the purview of Structure and Bonding to the extent that the focus... 

Two halide-centered cubane silver cluster complexes, containing discrete units, [Ag8X Se2P(OEt)2 6][PF6], or unidimensional chains, Ag8X[Se2-P(OEt)2]6X ra (X = Br and Cl) have been reported. This is an interesting case where the counter ions dictate the molecular/supramolecular architecture.440... 

Each of the examples (5.1)—(5.4) illustrates the linking of molecules into supramolecular species that constitute new units of liquid, gaseous, or solid phases. Other provocative examples of supramolecular aggregation include the al-lotropic phases of sulfur (composed of a variety of linear and cyclic polymeric chains)9 and the remarkable Zintl salts (with anions composed of variable metal clusters).10... 

Supramolecular aggregations are commonly referred to by a variety of terms, including adduct, complex, and van der Waals molecule. In this chapter we shall primarily employ the more neutral term cluster, which may, if desired, be qualified with the type of intermolecular interaction leading to clustering (e.g., H-bonded cluster ). General and specific types of intermolecular forces are discussed in the following sections. 

The nature of the noncovalent bonds that link molecules into supramolecular clusters has inspired discussion and speculation throughout the history of valence theory. Werner s transition-metal studies originally led to the concept of near-valence ... 

At shorter distances, particularly those characteristic of H-bonded and other charge-transfer complexes, the concepts of partial covalency, resonance, and chemical forces must be extended to intramolecular species. In such cases the distinction between, e.g., the covalent bond and the H-bond may become completely arbitrary. The concept of supramolecular clusters as fundamental chemical units presents challenges both to theory and to standard methods of structural characterization. Fortunately, the quantal theory of donor-acceptor interactions follows parallel lines for intramolecular and intermolecular cases, allowing seamless description of molecular and supramolecular bonding in a unified conceptual framework. In this sense, supramolecular aggregation under ambient thermal conditions should be considered a true chemical phenomenon. 

Two hexanuclear zinc clusters are mentioned elsewhere in this Chapter, one in Section V.A.7 (on zinc(II) reactions) above, the other in Section VII.D (on supramolecular chemistry) below. 

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