Supramolecular transition metal compound

Since we essentially deal with transition-metal compounds in this chapter, we, in this section, present a brief introduction to the main characteristics of rare earth complexes, where the reader can find references to more detailed accounts. The lanthanides show a marked preference for the - -3 oxidation state, and present very similar coordination and organometallic chemistries, with small differences associated only with changes in the atomic size along the series. The interest for the incorporation of lanthanides in supramolecular architectures is associated with Iheir magnetic and light emitting properties. 

The complexation of coordination compounds may make it possible to control their photochemical behaviour via the structure of the supramolecular species formed. For instance, the binding of cobalt(m) hexacyanide by macrocyclic polyammonium receptors markedly affects their photoaquation quantum yield in a structure-dependent manner [8.73-8.77]. It thus appears possible to orient the photosubstitution reactions of transition-metal complexes by using appropriate receptor molecules. Such effects may be general, applying to complex cations as well as to complex anions [2.114]. 

Early work on the kinetics of photoinduced ET in transition metal complex systems focused exclusively on bimolecular reactions between transition metal chromophores and electron donors or acceptors. However, concomitant with the advances in rapid photochemical kinetic methods and chemical synthetic methodology, emphasis shifted to photoinduced ET in chromophore-quencher assemblies that comprise a metal complex chromophore covalently linked to an organic electron donor or acceptor [24]. These supramolecular compounds afford several... 

A lot of photoreactions occurring in the atmosphere, hydrosphere, and soils ensure the health, comfort, and welfare of human beings, creatures, and the environment. These processes are mostly driven by coordination compounds of transition metals, which play the role of (photo)catalysts or (photo)sensitizers. There is also increased understanding of the role of supramolecular inorganic systems in their interaction with light and the great variety of processes that may ensue. 

Since Prussian blue chemistry is currently enjoying an active revival, several groups are exploring the closely related octacyanometalate building block [M(CN)8]", where M is a transition metal ion, for the self-assembly of novel supramolecular coordination compounds [20,68]. 

This thinking applies, in particular, when planning the design of a chiral three-dimensional supramolecular host-guest system, since the mutual interaction of the two distinct complementary molecular units or coordination entities is necessary. Examples of this methodology include the above-described anionic, tris-chelated transition metal oxalato complexes [Mzl(ox)3/6 which form the host system together with the cationic, tris-chelated transition metal diimino complexes, e.g. [M(bpy)3]21/31, bpy = 2,2 -bipyridine, which play the role of the guest compounds. 

A large number of covalently linked systems are currently being synthesized and investigated, differing in the nature of A, B, and L, as well as in the number of functional units in the supramolecular system (nuclearity). It is common to call simple two-component donor-acceptor systems such as that of Eq. 2 dyads , and progressively more complex systems triads , tetrads , pentads , etc.. Systems where all the A and B units are organic molecules are dealt with in Chapter 1 of this section. The present chapter deals with systems where at least one of the A/B functional units is a transition metal coordination compound. From this definition, however, are excluded (a) systems where A and/or B are porphyrins or related species (dealt with in Chapter 2) and (b) systems of high nuclearity with dendritic structures (dealt with in Chapter 9). 

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