Supramolecular adducts

This supramolecular approach has been used as a way to facilitate the crystallization of cuboidal aqua ions and to capture single intermediates present in complex solution mixtures. For example, [M3Q4Clx(H20)9.x] (Q = S, Se) supramolecular adducts have been isolated for x =1-5 from aqueous HCl solutions by varying the acid concentrations where the aggregates contain in each case only one of all possible isomers [46]. In addition to the hydrogen bonds, other kinds of interactions, namely C1---H20, C1---C1 and Q---Q contacts, are also involved in the network propagation. This supramolecular approach has also been efficiently employed for the crystallization of a large number of aqua complexes within the [M3M Q4] cubane-type family, where M is a transition or post-transition metal [47]. 

This entry to supramolecular chemistry allows one, at the same time, to develop a host-guest chemistry because the space inside the cucurbituril barrel is sufficient to confine small "guesf molecules. This is illustrated with the crystallization of the supramolecular adduct [W3S4(H20)8Cl](pyH ccuc) Cl4a 5.5 H2O with a pyridinium cation inside the cucurbituril cavity [48]. The introduction of guest molecules may vary the net charge on the assembly and consequently the whole packing in the solid state. 

The relaxivity enhancement associated with exchangeable protons in the second-coordination sphere of a Gd(III) complex is quite important in the supramolecular adducts of Gd(III)-based systems with proteins. For example, it has been reported that, besides water protons in the second-coordination... 

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. 

Figure 2.71 Cso may form supramolecular adducts with a variety of compounds, for example, with derivatives of porphyrine (a), cyclodextrines (b), calixarene (c) or crown ethers (d).

Chlathrates may, in a way, be regarded as supramolecular adducts in the crystalline state. C ) forms a series of these compounds which in most cases are obtained by simple cocrystallization of their constituents. Known examples are the inclusion compounds with hydrocarbons tike pentane or nonane, etc., but chlathrates of Qo or C70 have also been found with hydroquinone in the presence of benzene. In these cases the fullerene molecules occupy interstitial spaces within the crystal structure of hydroquinone and form donor-acceptor complexes. Further inclusion compounds with fuUerenes are known for ferrocene and other inorganic substances such as sulfur (Sg), white phosphorus (P4) or complexes hke (PhCN)2PdCl2 and PhsPAuCl (also refer to Section 2.5.3). For the complex of > with ferrocene the crystal structure of the first is found with the latter inserted into the given gaps. The whole stracture can only exist because ferrocene is too weak a reducing agent to transform > into Qo. 

Reactions Between Solids for the Preparation of Supramolecular Adducts 576... 

Owing to the thermodynamic and kinetic stability of the Ru-pyridyl bonds, solutions of 9Zn can be treated with excess of other N-ligands without the occurrence of decomposition or scrambling processes. Thus, 9Zn is a rigid 2D module with two central junctions that can be exploited for the construction of more elaborate supramolecular adducts upon treatment with appropriate polytopic ligands. 

As unambiguously evidenced by NMR spectroscopy, titration of 9Zn in CDCI3 solution with one equivalent of a linear ditopic N-ligand leads rapidly to the quantitative assembling of sandwich-like 2 2 supramolecular adducts of formula [(9Zn)2(Ar-L)2j (L = 4,4 -bipy, 13 L = 4 -fransDPyP, 14 L = 4 -tra sDPyP-npm, 15), formed by two parallel metallacycles connected by two bridging ligands which are axially bound to the zinc-porphyrins (Scheme 3) [68,72,73]. 

The other critical parameter to consider in the formation of supramolecular adducts is their shape. According to what was stated above, the molecular ellipticity a/b) must be higher than 3 so that /s is relevant. Thus, when spheroid elemental building blocks without particularly directional... 

---