Catenanes three-state

Controlled rotation of the molecular rings has also been achieved in catenanes composed of three interlocked macrocycles. For example, catenane 42H26+ (Fig. 13.37) is made up of two identical macrocycles 2 interlocked with a cyclophane containing two bipyridinium and two ammonium units.44 Because of the type of the macrocycles used, the stable coconformation of 42H26+ is that in which the two rings surround the bipyridinium units (Fig. 13.37a, state 0). Upon addition of one electron in each of the bipyridinium units, the two macrocycles move on the ammonium stations (Fig. 13.37b, state 1) and move back to the original position when the bipyridinium units are reoxidized. 

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. 

Of these three systems, Cu.31 is the most promising compound in relation with electrochemically induced molecular motions, due to the perfect chemical reversibility of the processes. Interestingly, the rates of the movements in rotaxane Cu.31 are very different from those measured for the related catenane Cu.25 (see Section 8.5) [95-97]. The conversion Cu"(4) to Cu"(5) is faster in Cu.31 than in Cu.25. This difference could reflect a greater ability of Cu (4j in Cu.31 to interact with solvent molecules or anions, the copper(ll) center being perhaps loosely bound to a fifth ligand which would thus stabilize intermediate states on the way to Cu"(5). 

Solid-state properties of the catenane copolymer were determined using DSC and dynamic mechanical analysis (DMA) and were compared with pure PC. DSC revealed a glass transition temperature of ca. 150°C for all the catenane copolymers 22 to 24, which is essentially the same as the pure PC sample of the same molecular weight. This insensitivity of the Jg to the presence of the catenane repeat unit is possibly on account of the considerable flexibility/mobiUty of these catenanes. DMA of the copolymer containing 20% (w/w) catenane showed three transitions at —100, —6, and - -80°C. The first and third transitions are observed in PC films while the —6°C was linked to the catenane ring/chain movements. 

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