Self-catenation

Figure 38. Self-penetrating, self-catenating structure of Cd(CN)2- pyrazine. Circles represent Cd. Short connections between Cd atoms represent cyano bridges within the (4,4) Cd(CN)2 sheets and longer connections represent the pyrazines linking sheet to sheet Two catenated 6-gons are highlighted.

Probably the first examples of 3D self-catenated frameworks within coordination polymers were described by Robson and coworkers [49], In the species [Cd(CN)2L] [L = pyrazine or l,4-bis(4-pyridyl)butadiene] the Cd(CN)2 sublattices form 44 undulated layers that are joined in a criss-cross fashion by the L spacers. Catenated hexagonal chair-like circuits are observed in the interlayer connections (see Fig. 

The Schlafli Symbols of these 6-connected nets are 48.66.8 (rob) for L = pyrazine, and 44.610.8 for L = l,4-bis(4-pyridyl)butadiene, respectively, so that the requirements for self-catenation are fulfilled, since the catenated 6-rings are the shortest rings [50], Perhaps one of the most fascinating examples is represented by [Ni(tpt)(N03)2] (tpt = tri-4-pyridyl-l,3,5-triazine) [51]. This contains a remarkable 3-connected chiral uniform net of 123 topology (twt, VS=124.12y. 127) (see Figure... 

Figure 1.3.9 Three examples of self-catenated nets with two catenated rings (Hopf links) in black 6-rings (rob), 8-rings (coe), 12-rings (twt).

Self-catenation is observed not only in 3D nets but also in 2D nets a few rare examples are known (see Ref. [3]) and two recent examples are the 4-con-nected layers in a Cd coordination polymer (G. O. Lloyd, J. L. Atwood, L. J. Barbour, Chem. Commun. 2005, 1845) and the 6-connected layers in a supramolec-... 

Fujimoto and coworkers used a self-assembled Janus [2]-pseudorotaxane406 to obtain a Janus[2]rotaxane 407 (Figure 8.2.4) [33]. A quadruply stranded alkaline earth metal containing helical catenate, a charge-neutral heterotopic homodinuclear [2]catenane, was reported by Castro et al. [34]. 

Experimentally, sodium nitrate was added to an aqueous solution of molecular ring 16, and the solution was heated at 100 °C. Then, the equilibrium between 16 and its catenated dimer 15 is pushed by the polar media toward the catenane. After self-assembling in a high yield, catenane 15 was isolated as a CIO4 salt in a high yield (Eq. 3). It was confirmed that catenane 15 thus obtained did not dissociate into two rings in aqueous solution because its framework had been locked. 

Successful self-assembly of catenanes 23 and 25 and their remarkable stability imply that rectangular box structures for the component rings are very effective for catenation. Thus, we also designed the construction of rectangular frameworks from a set of 11 and two different ligands. Surprisingly, these three-component systems worked very well and we observed highly efficient three-component-... 

Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of complex structures, namely of cyclic multiporphyrin arrays [9.13a, 9.179], of inorganic rotaxanes [9.97a, 9.180], of multi-catenates and catenands (see 181) [8.281, 8.282] and even of molecular knots (see 182) [8.282, 9.77, 9.181] (in 181 and 182 a) with, b) without Cu(l) template). 

There are two distinct approaches to catenane synthesis the statistical approach, and approaches relying on self-assembly, so-called directed synthesis . The statistical approach relies on the small chance that macrocyclisation may occur while a linear precursor is threaded through a macrocyclic component. Because this is a rather unlikely eventuality, it naturally results in low yields of interlinked product and is chiefly of historical interest. It was this kind of statistical approach that resulted in the first synthesis of a [2] catenane by Wasserman in 1960 (10.64), from cyclisation of the long-chain diester 10.65 while threaded through the annulus of a deuterated C34 cycloalkane 10.66 (Scheme 10.11), 57 Although the overall yield of the catenation reaction was less than 1 %, the existence of the catenane was firmly established. The relatively polar [2] catenane product, along with other polar macrocyclisation reaction products and... 

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