Self metal coordination

In the last example, a serious handicap is the extreme sensitivity of the calculations to the parameterization of the metal atoms. In a paper concerning the spin states of metal dimer complexes (38) as studied by EHT, heavy manipulation of the original theory was needed. In the field of transition metal coordination compounds self-consistent charge (SCC) calculations (of the type already mentioned for electronegative atoms) are essential to obtain the diagonal elements Hu. 

The encapsulation of classical and organometallic transition-metal complexes to yield molecules of the type complex in a complex is a very attractive research area. A variety of inclusion complexes of this type has been reported. Of relevance for this review are reports on the encapsulation of coordinatively unsaturated transition-metal complexes inside self-assembled coordination cages (120), cyclodextrins (121,122), and cucurbiturils (123). 

Metal coordination is another important bonding opportunity with respect to self-assembly. This is important in many natural molecules such as hemoglobin and chlorophyll, where the metal atom acts both as the site of activity and as a centralizing agent with respect to shape and thus acts as a nucleating agent for self-assembly. 

Another fascinating approach to catenanes via self-assembly involves metal-coordination which templates or directs the assembly of catenane frameworks. After brief discussions on the recent examples of metal-containing catenanes and related topologically interesting molecules (Sections 4.2.1-4.2.3), the focus will be on the self-assembly of Pd(II)-linked catenanes (Sections 4.2.4 and 4.2.5). 

These considerations also apply to systems where binding involves interactions other than metal coordination, such as hydrogen bonding or donor-acceptor forces. Such is the case for the chiral selection occurring in the course of the self-assembly of homochiral helical strands (Section 9.4.2) and ribbons (Section 9.4.4) through hydrogen bonding. 

Such complexes form a precursor to a full discussion of the vast and highly topical field of self-assembly (Chapter 10). We consider them here since they resemble structurally the types of compounds discussed in Section 4.7, but unlike metal-based anion receptors the simple thermodynamic equilibrium between host, anion and complex is not the only process occurring in solution. In fact multiple equilibria are occurring covering all possible combinations of interaction between anions, cations and ligands. These systems have the appeal that the formation of particular metal coordination complexes are thus subject to thermodynamic anion templating (cf. the thermodynamic template effect in macrocycle synthesis, Section 3.9.1) and vice versa. 

In this chapter, we describe the synthesis of a series of self-assembled metal coordination polymers that show various color emissions from the violet to red spectral region with high PL quantum yields and good OLED efficiencies. 

The self-assembly of small molecules into complex material based on a multitude of different noncovalent interactions, such as hydrogen bonding, ionic interactions, hydrophobicity and metal coordination, has been established over the last century [2, 30, 38, 44-49]. In this context, the real power of self-assembly becomes evident when not only multiple noncovalent interactions but also multiple levels of self-assembly occur within the same small molecule system. These multiple tiers of self-organizational hierarchy can yield highly complex structures with sec-... 

Fig. 7.16 Multi-step main-chain self-assembly to form a flexible, high molecular weight polymer. Step 1 dimerization of bifunctional unit via the self-complimentary ureidopyrimidinone end (top). Step 2 addition of a metal salt such as iron(ll) initiates metal coordination-based self-assembly of the trpy-functionalized ends to form extended polymer chains (bottom).

In 2004, Week and co-workers demonstrated that both mono- and multifunctional self-assembly could be employed simultaneously independently and reversibly on the same side-chain functionalized polymer [96]. A random terpolymer of poly(norbornene) was synthesized consisting of diaminopyridine (DAP) hydrogen-bonding receptors and a palladium-functionalized SCS-type pincer ligand for metal coordination-based self-assembly (Fig. 7.18). 

An interesting dimension of metal-coordinated self-assembly that is often ignored, or at least not exploited to its fullest extent, occurs when the resulting coordination complex is a charged species and, as such, in need of a counterion. This counterion itself presents yet another subtle instance of ionic self-assembly, which often is overshadowed by its partner, the coordination complex. The second multi-functional side-chain supramolecular polymer system is based on this simple but important concept [14, 106-111]. In 2003, Ikkala and coworkers reported a study in which they exploited (1) a side-chain functionalized polymer, poly(vinyl-pyridine), (2) metal-coordination self-assembly via a tridentate Zn2+ complex and (3) ionic self-assembly through functionalized counterions, i.e. dodecylbenzene-sulfonate ions, to form multiple self-assembled complexes which adopted a cylindrical morphology (Fig. 7.23) [112]. 

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