Dynamic structural diversity

The most striking feature of 863-883 is their structural diversity in solution and the solid state. In solution, dynamic equilibria exist between penta- and hexacoordinated species, which have been probed by NMR spectroscopy (Scheme 123). 

The diverse nature of chemical bonding arrangements exhibited by humus enables the formation of associations both with non-humic materials and with other humic materials to create a dynamic structure. Such a structure is capable of undergoing inter- and intra-molecular bonding to add or lose constituents or change configuration in response to ambient conditions. The chemically diverse and highly reactive nature of the humic matrix imparts the ability of humus both to lose and to acquire molecular moieties in a dynamic manner. 

Additionally, nucleic acid bases have been used in the dynamic assembly of mixed-metal, mixed-pyrimidine metallacalix[n]arenes [47]. In this approach, Lippert and coworkers investigated the dynamic assembly of metallacalixarenes based on platinum (Pt ), palladium (Pd°), uracil, and cytosine assemblies with mixed amines. These combinations form cyclic metallacalix[n]arenes structures with n = A and = 8. Of the metallacalix[4]arenes, compounds were formed with five, six, and eight bonded metals, and a variety of nucleobase coimecfivities (UCUC and UCCU). The dynamic nature of this assembly allows access to novel and structurally diverse set of nucleobase metallacalixarenes. 

This chapter will outline the synthesis of polymeric materials pursuing structural diversity and prepared by equilibrium reactions through DCLs. In particular, the dynamic covalent polymers will be focused upon because of their high stability and processability. In addition, advanced approaches to polymeric materials in DCC will be outlined. In this chapter, the authors will only discuss covalent polymers, excluding noncovalent polymers (supramo-lecular polymers) that can be found in References 7 and 8. 

The merging of the features -information and programmability, -dynamics and reversibility, -constitution and structural diversity, points to the emergence of adaptive and evolutive chemistry, towards a chemistry of complex matter. 

PBSA), the lambda dynamics approach and the chemical Monte Carlo/Molecular dynamics approach. Success using these methods will depend on their ability to accurately discriminate between structurally diverse compound series and thereby help prioritize the compound series for the medicinal chemists. 

In this chapter, crystalline-state photochromic dynamics of rhodium dithionite complexes are reviewed. The chemistries described here have been achieved not only by recent developments of the analytical technique but also by discovery of a new class of transition-metal based photochromic compounds. One of the advantages of transition-metal complexes is structural diversity. In order to find the rule of an exquisite combination of metal ions and ligands, we are currently synthesizing various dithionite derivatives with other metal ions and/or modified Cp ligands. As shown in this chapter, dithionite complexes are a very useful photochromic system to investigate crystalline-state reaction dynamics. We believe that dynamics studies of newly synthesized dithionite derivatives provide useful insight into the construction of sophisticated molecular switches. A dithionite complex may appear in a practical application field in the near future. 

There is some difficulty with using an intuitive notion of complexity, as we have been. How can we decide more precisely what we mean by "complexity" of a system The initial intuition is that any system is more complex than any of its proper subsystems. The solar system example shows that this intuition fails when the focus with which the system is considered changes. An alternative intuition is that the complexity of a system might be measured by the number and diversity of its component atomic entities (in this sense, an entity is atomic in any consideration of a structure if we do not inquire into its substructure). This also fails in that it does not deal well with the fact that a static structure, or an instantaneous snapshot of a structure, is a less complex entity than a dynamic structure that contains the same atomic units. There may be an information theoretic measure of the complexity of a system in terms of the number of bits of information required to specify its observable properties at the required focus. 

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