Supramolecular ladders

In the structure of (A,A -bis(salicylidene)ethane-l,2-diamine-A,A ,0,0 )tin(II) (14), a four-coordinate donor set, akin to those found in the structures of 11 and 12, is found, but in this case the donor set is N2O2, derived from two symmetrically chelating N,0-bidentate ligands. As with previous examples, Sn... tt interactions connect molecules into pairs around a crystallographic two-fold axis of symmetry. The dimeric aggregates are linked into a linear chain, with the topology of a supramolecular ladder, via well-defined pairs of bifurcated C-H... O interactions (2.62 A and 2.66 A), as shown in Figure 3.9.9. 

Figure 38 Possible supramolecular architectures based on the 4,4 -bipyridine ligand, (a) Linear chain when [M] is a metal/secondary building unit forming two diagonally opposite bonds, (b) supramolecular ladder, and (c) supramolecular square.

The progression from elementary particles to the nucleus, the atom, the molecule, the supermolecule and the supramolecular assembly represents steps up the ladder of complexity. Particles interact to form atoms, atoms to form molecules, molecules to form supermolecules and supramolecular assemblies, etc. At each level novel features appear that did not exist at a lower one. Thus a major line of development of chemistry is towards complex systems and the emergence of complexity. 

Very recently, MacGillivray et al. succeeded in the supramolecular construction of molecular ladders in the solid state using a linear template approach [48]. They designed the cocrystals 1,3-benzenediol (resorcinol) or a derivative with an all-trans-bis(4-pyridyl)butadiene or hexatriene, in which two resorcinol molecules preorganize two polyene molecules through two hydrogen bond interactions, for [2-1-2] photoaddition (Scheme 5). In this design, two polyenes would... 

Metal-directed Self-assembly of Complex Supramolecular Architecture Chains, Racks, Ladders, Grids, Macrocycles, Cages, Nanotubes and Self-intertwining Strands (Helicates)... 

Supramolecular Arrays of Metal Ions. Racks, Ladders, Grids... 

Only one diorganotin-based supramolecular compound with twelve tin atoms, namely [Me3SiCH2(Cl)Sn(CH2)3Sn(Cl)(CH2)3Sn(Cl)CH2SiMe3]Oi.5 4 (108)227, has been reported so far. The structure consists of three almost planar Sn4Cl402 layers. Each layer is connected to the next layer by four trimethylene chains to give a triple ladder structure. 

Figure 6. Formation of a linear ladder-type supramolecular polymer (14) or a hydrogen-bonded network (15) based on the single hydrogen bond between a pyridine unit and a benzoic acid unit.

Once the first double-ladder-type compound had been established it was apparent that systematic study of this class of compounds should be conducted and a number of questions in context with the structures (A), (B), and (C) shown in Scheme 2.10.12 be addressed. Thus, we were and still are interested in studying the influence the identity of the spacers Z, the organic substituents R, and the electronegative substituents X and Y have on which structure is acmahy observed in solution and in the solid state, and whether these structures can be inter-converted. Furthermore, we looked at the possibility of extending the concept from double to multiple ladder-type structures and made the first attempts to assemble tetraorganodistannoxanes with double ladder-type structures to give supramolecular networks. 

Future efforts might be devoted to employing tetraorganodistannoxanes with double and triple ladder structures as organometallic secondary building units in supramolecular chemistry. 

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