Rotaxane-type

A rack-like arrangement schematically represented by 160, would be formed by the complexation of several metal ions to rigid, linear sequences of binding sites. Thus, binding of bipy or phen units to 155 and to its extended tri- and tetratopic analogues present in 157 and in 158 via metal ions of tetrahedral coordination such as Cu(l) and Ag(l) should yield rack structures of type 160. With the bipy or phen unit included in a macrocycle, inorganic rotaxane-type structures (see also Section 9.6) such as 159 have been obtained [9.97a]. A linear sequence of connected terpy sites such as 161 yields racks with individual terpy units and metal ions of octahedral coordination [9.97b]. 

Figure 10.63 Crown ether ammonium ion based rotaxane type hydrogen bonded complexes (a) [3] rotaxane, (b) three threads in one ring and (c) two threads linking two rings.

The hydrogen bonding of ammonium ions to crown ethers has also been used to assemble a range of rotaxanes andp. eMd/orotaxanes. The inclusion of a secondary ammonium thread into dibenzo[24]crown-8 followed by covalent capping to give a rotaxane is shown in Scheme 10.19. This kind of approach can result in some interesting multiply threaded rotaxane type compounds, Figure 10.63. 

The rack-type architecture can be assembled also from tetrahedral metal ions, e.g., Cu. linear polytopic hgands with tetrahedral pockets (El), and bidentate hgands such as phenathroline or 2.2 -bipyridyl. One example is illustrated in Fig. 3b. It is a rigid rack of rotaxane-type. the ancillary ligand being a macrocychc molecule with a 1,10-phenathroline moiety. 

Fig. 3 Racks (a) rack constructed from octahedral Ru(II) ions (b) rotaxane-type rack constructed from tetrahedral Cu(I) ions.

ACRONYM, ALTERNATIVE NAME Inclusion complex, molecular necklace (MN), string of pearls, rotaxane-type polymer, polymeric rotaxane. 

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