Catenanes solid state structure

Figure 15. The template-directed synthesis of the [2]catenanes 32-4PF6-384PF6. The insets show (i) the intermediate [2]pseudorotaxane formed during the course of catenane formation and (ii) the solid-state structure of the [2]catenane 324+.

Figure 33. The template-directed syntheses of the [2]catenanes 109 and 110 and of the [3]catenanes 112 and 113 as well as the solid state structure of 110.

Figure 7-45. Two views of the solid state structure of the [3]-catenane 7.64. The large ring formed from the coupling of the 7.65 ligands has been coloured black and the two macrocyclic ligands 7.63 white. The second view, along the Cu—Cu axis, emphasises the folded structure of the large, central macrocyclic ring and shows some of the 7t-stacking interactions that are responsible for the adoption of this conformation.

Likewise, three-dimensional renderings of MIMs remind us instantly of some of the ordinary objects we encounter in our everyday lives (see Sect. 2.3). Take olympiadane [82], for example (Fig. 13), with its five interlocked rings unmistakably sharing the same topology as the Olympic logo Most catenanes bear resemblance at least to the links of a chain, as their name implies. Regardless of their resemblance to familiar objects, hundreds of beautiful crystal structures of MIMs have been produced since their debut in 1985, when Sauvage [83] published the first solid-state structure of a [2]catenane (Fig. 14a). It would be impossible to do justice to all of the beauty contained in the databank of solid-state mechanically interlocked structures. In Fig. 14 we simply present a few examples that we find noteworthy [84—88]. See Fig. 23 in Sect. 4.2 for more beautiful crystal structures of some particularly novel MIMs. 

Fig. 29 Solid-state structure of the doubly interlocked [2] catenane (Solomon Knot) that emerges unexpectedly from a DCL containing DAB, DFP, and a 1 1 mixture of Zn2+ and Cu2+templates [217]...

Facile synthesis and solid-state structure of a benzylic amide [2]catenane, A. G. Johnson, D. A. Leigh, R. J. Pritchard and M. D. Deegan, Angew. Chem. Int. Ed. Engl, 1995, 34, 1209. 

So far, we have addressed the construction and properties of polyrotaxanes, incorporating one or more tetracationic cyclophanes on 7C-electron rich dumbbells Figure 4a), Formalistically, we could also extrapolate in our minds from the solid state structures of the [2]catenane to polyrotaxanes which incorporate one or more bis-paraphenylene-34-crown-lO macrocycles onto 7C-electron deficient dumbbells Figure 4b). We shall now discuss the initial approaches that have been developed for constructing such polyrotaxanes. 

Figure 17.14 Schematic representation of a solid-state device based on junctions consisting of a monolayer of catenane [ 131 [ I ) 11 A 11 sandwiched between polysilicon and Ti/Al electrodes.115 The structures of 134+ and DMPA- are shown in Fig. 17.12. (Adapted with permission from V. Balzani et al., ChemPhysChem 2008, 9, 202—220. Copyright Wiley-VCH Verlag GmbH Co. KGaA.)...

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Fig. 5 Typical examples of (a-c) self-assembling inclusion hosts (d-f) interlocked and interwoven systems and (g-j) solid state inclusion hosts (a) tennis ball dimer (b) metallamacrocycle (c) ladder-structured metal array (d) catenane (e) rotaxane (f) helicate (g) network lattice host (exemplary host molecule) (h) coorclinatoclathrate host (exemplary hosts) (i) curved framework host molecule and (j) aukward-shape host molecule.

These examples show how redox conversions can be utilized to control internal motions and the relative positions of functional groups in interlocked structures, such as catenanes and rotaxanes. Recently, the groups of Stoddart and Heath demonstrated that these compounds can be used to build monolayers, anchored with phospholipid counterions, which exhibit properties like those of solid-state, electronically addressable, switching devices. 

A wide range of instrumental techniques are needed to characterise products fully - X-ray crystallography, mass spectrometry (especially FAB-MS and electrospray MS), H and NMR, UV-Vis spectroscopy, and electrochemistry - in the solid state and in solution. As much information as possible is needed in order to establish both the exact nature and long-range structural features (superstructure) of rotaxanes, catenanes and knots. As noted at appropriate points in the text, there is considerable interest in applications for these classes of compounds, particularly in respect to molecular switching devices. 

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