Boxes, molecular

Molecular boxes , capable of binding a decanediyldiammonium or dodecanediyl-diammonium ion in their cavities, have been constructed from diazacrown ethers and pendant nucleotide bases. ° For example, structure 25 is based on hydrogen-bonded adenine-diazacrown-adenine and thymine-diazacrown-thiamine monomer units. The bis(ammonium) salt interacts with the oxygen atoms of two azacrown rings contained in each half of the cyclic 1 1 host-guest box . Characterisation of this product was largely performed using H-NMR spectroscopy and vapour 

The bis-porphyrin supramolecular box 26 has also been assembled using a molecular recognition process involving hydrogen bonding between pendant-arm 

Three equivalents of a calix[4]arene derivative, diametrically substituted at its upper rim with two melamine units, have also been demonstrated to yield well-defined box-like assemblies on interaction with six equivalents of 5,5-diethylbar-bituric acid. The product, which is based on an extended rosette motif, consists of nine different components held together by 36 hydrogen bonds. It is stable in apolar solvents and remains so even at very low concentrations. Further, the structure remains intact in the solid state, as confirmed by an X-ray diffraction study. In an extension of this study, three enantio-pure calix[4]arene-dimelamine derivatives were employed for a parallel study. In this instance, the chiral information in the individual calixarene derivatives proved successful in controlling the conformation of the final assembly - a homochiral supramolecular entity was the result. 

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Figure 1.13 Self-selection of molecular boxes via olefin metathesis.

Vieekamp RH, van Duynhoven JPM, Hubert M, Verboom W, Reinhoudt DN. Molecular boxes based on calix[4]arene double rosettes. Angew Chem Int Ed Engl 1996 35 1215-1218. 

Quantitative Formation of Catenanes from Rectangular Molecular Boxes... 

As discussed in the last section, the driving force for the self-assembly of cate-nane 13 is the efficient aromatic contact between two monomer rings. Therefore, we designed a rectangular molecular box 21 containing Pd(II)-pyridine coordinate bonds. 

A new type of iodonium salts constitute the conformationally rigid, tetranu-clear macrocyclic ring systems dubbed molecular boxes. The relatively simpler tetraaryltetraiodonium salts were obtained from 4,4 -bis(diacetoxyiodo)bi-phenyl and 4,4 -bis(trimethylsilyl)biphenyl [119]. The iodonium salt derived from 4-(4 -lithiophenyl)pyridine was made using the method of /J-(dichloroio-do)chloroethylene and it was used for the construction of hybrid iodonium-platinum (or palladium) cationic tetranuclear macrocyclic squares including some in which the ligand of the metal was a chiral biphosphine [120,121]. 

The cyanometalate box Cs c [Cp Rh(CN)3]4[Mo(CO)3]4 3 is formed in low yield from the reaction of [Cp Rh(CN)3] (Cp = CsMes) and (/ -CeHtMet )Mo(CO)3 in the presence of cesium ions, and it can be crystallized as a Et4N+ salt. The Cs+ ion serves as a template in the self-assembly of the anionic molecular box, which has a cubic Rh4Mo4(/r-CN)i2 core with three exterior carbonyl ligands attached to each Mo and a Cp group to each Rh. The encapsulated Cs+ ion has a formal coordination number of 12 if interaction with the centers of cyano groups is considered (Fig. 20.3.15). 

Schall O, Gokel GW (1994) Molecular boxes derived from crown ethers and nucleotide bases probes for Hoogsteen vs Watson-Crick H-bonding and other base-base interactions in self-assembly processes. J Am Chem Soc 116 6089-6100... 

Timmerman P et al (1997) Noncovalent assembly of functional groups on calix[4]arene molecular boxes. Chem Eur J 3 1823-1832... 

Ramesh M, Rauchfuss TB (2004) Structural and mechanistic studies on ion insertion into the molecular box [CpCo(CN)3]4[Cp Ru]4. J Organomet Chem 689 1425-1430... 

For dynamic processes involving hydrogen-bonded entities, see (a) Calama MC et al (1998) Libraries of non-covalent hydrogen-bonded assemblies combinatorial synthesis of supramolecular systems. Chem Commun 1021-1022. (b) Timmerman P et al. (1997) Noncovalent assembly of functional groups on Calix[4]arene molecular boxes. Chem Eur J 3 1823-1832. (c) Cai MM et al. (2002) Cation-directed self-assembly of lipophilic nucleosides the cation s central role in the structure and dynamics of a hydrogen-honded assembly. Tetrahedron 58 661-671... 

Double molecular box molecular architecture that resembles two cubes (or boxes) fused at one comer Functional materials molecular materials that are designed to perform specific fimction(s)... 

Onclin, S. Huskens, J. Ravoo B. J. Reinhoudt, D. N. Molecular Boxes on a Molecular Printboard Encapsulation of Anionic Dyes in Immobilized Dendrimers. Small 2005, 852-857... 

In an extension of this basic approach, Stang and Zhdankin have prepared molecular boxes with four iodonium ions as comers and four biphenyl groups as sides in a structure directly analogous to (22) [35]. 

Schall and Gokel have reported the construction of molecular boxes derived from nucleic acid bases and azacrown ethers [23]. Detailed NMR studies provided evidence for the association of A-crown-A with T-crown-T in chloroform. Formation of a ternary receptor complex with a, m-diammonium compounds (Figure 12) was also suggested. 

Figure 12 The complex from a molecular box and a diammonium guest [23]...

Our intention in this chapter is to draw attention to the chiral aspects of self-assembled polynuclear complexes, and to show how the study of properties related to chirality can afford useful information. After a brief review of the nature of chiral centres in these complexes and the experimental methods used for studying them, we will discuss a number of structure types which are currently attracting interest, such as helicates, dendrimers, molecular boxes, and topologically complex molecules. 

These compounds enjoy a number of advantages over their organic counterparts, in particular, one-pot reactions, high yields, spectroscopic, electronic, and magnetic properties, which are inaccessible with organic species [20,21], Furthermore, the use of transition metal coordination has been explored by Lehn and co-workers and many others. The new strategy was successfully used for the construction of molecular racks [1,22], ladders [1,11,23], grids [1,11,24,25], squares [7,26,27], cylinders [11,28], molecular boxes [29], catenanes [13,15,30], rotaxanes [31], knots... 

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