Ionic supramolecular complexes

Supramolecular polymeric complexes without aromatic mesogens can exhibit liquid-crystalline phases due to microphase segregation [112-117]. Complex 32 consisting of poly(4-vinylpyridine) complexed with alkylphenol shows a layered mesophase (Figure 24) [112]. Ionic supramolecular complex 33 based on poly(ethyleneimine) and alkanoic acids also forms layered mesophases (Figure 24) [115]. 

Ionic supramolecular self-assembly will be discussed in Chapter 6, but some supramolecular systems based upon ionic interactions will be discussed earlier, e.g. the organocyclosiloxanolates, which form sandwich compounds by intercalating transition metal ions between two macrocyclic rings (held together by ionic interactions) and acting as endo receptors which concurrently have crown-ether-type complexing properties (as exo receptors) (see Section 2.1.2). 

In the following sections, we will review the various different ways in which comb copolymer-like architectures (supramolecular comb copolymers) mi t be obtained using noncovalent physical interactions, e.g., ionic, coordination complexation, or hydrogen bonding see Figure 8. 

Reichert WM, Holbrey JD, Vigour KB et al (2006) Approaches to crystallization from ionic liquids complex solvents-complex results, or, a strategy for controlled formation of new supramolecular architectures Chem Commun 4767—4779... 

Two types of micellar systems have been described, the first one includes Gd complexes capable of self-organization resulting in a supramolecular assembly 103), while the other class of micelles, also named mixed micelles is made of several components a lipophilic gadolinium chelate, one or several phospholipid(s) and a non-ionic surfactant containing a polyoxyethylene chain 104,105). 

Having introduced the major principles of complexation, association, and organization, it is important to review the physicochemical forces that lead to supramolecular ensemble formation. As mentioned above, supramolecular interactions are by definition noncovalent. In the order of the polarity of the partners involved, they comprise ionic or electrostatic interactions,17 18 ion-dipole interactions,19 dipole-dipole interactions, (ionic) hydrogen bonding, cation-tt and anion-tt interactions,... 

Functionalized N-triethylene glycol pyrrolidino-CNTs (Fig. 1.10a) allowed electrochemistry and quantum chemical calculations to be carried out to investigate the bulk electronic properties [167]. Functionalization obviously modified the electronic state of pristine CNTs however, some of the metallic character was retained and the overall electron density of states (DOS) was not strongly affected [167]. Pyrrolidino-SWCNTs and -MWCNTs bearing a free amino-terminal N-oligoethy-lene glycol moiety formed supramolecular associates with plasmid DNA through ionic interactions. The complexes were able to penetrate within cells. SWCNTs... 

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]. 

The earliest recognised examples of synthetic supramolecular structures were the complexes formed from crown ethers and metal cations [19]. Since then numerous macrocycles have been synthesised. Representative examples are the cryptands [20], These differ from crown ethers in that the former contains a tridimensional cavity while the latter are characterised by a hole. Similarly, calix[4]arenes are compounds with a cup -like structure that through lower rim functionalisation gives rise to a hydrophilic and a hydrophobic cavity, thus allowing the reception of ionic species in the former and neutral species in the latter. Most of the above mentioned macrocycles are known for their capability to serve as cation receptors. 

Fullerenes C60 and C70 form supramolecular adducts with a variety of molecules, such as crown ethers, ferrocene, calixarene, and hydroquinone. In the solid state, the intermolecular interactions may involve ionic interaction, hydrogen bonding, and van der Waals forces. Figure 14.2.9 shows a part of the structure of [K(18C6)]3-C6o-(C6H5CH3)3, in which Cgg is surrounded by a pair of [K+(18C6)] complexed cations. 

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

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