Pyridines supramolecular assembly

Sanders (83) constructed a supramolecular assembly of heterometal-lic porphyrins held together by different types of metal-ligand interaction. The team exploited the different kinetic and thermodynamic properties of the pyridine-zinc, carboxylate-tin, and pyridine-... 

A helical homobimetallic mercury(II) complex with a bridging bis(NHC) ligand serves as a starting point for a supramolecular assembly. Also tetrameric cyclic palladium(II) complexes have been obtained with bridging NHC-pyridine ligands. 

Pyridine is widely used as a solvent that also ligates a number of transition metals through an aromatic nitrogen donor. From this perspective it has little importance in facilitating supramolecular assembly but fortunately the pyridine morif can be incorporated in numerous derivatives. A single pyridine molecule can form the basis... 

Five helical strands associate laterally leading to a quintuple helical braid (Figure 29). The authors [49] suggested that the formation of this supramolecular assembly may be due to edge-to-face interactions between the pyridine units and the phenyl groups in conjunction with van der Waals interactions. Finally, the quintuple helices associate laterally to form the crystal. In this supramolecular synthesis H-bonding plays a role only in the first level of the assembly process via a single-stranded H-bonded helical network. 

Pyridine moieties can also have H-bonding interactions with other H-bond donors to create nanostmctured materials, as shown by Stamm et al. [44]. Well-ordered nanostmctured thin polymer films from the supramolecular assemblies of PS-P4VP and 2-(4 -hydroxybenzeneazo)benzoic acid (HABA) have been fabricated (Fig. 2.6) [44]. This assembly formed cylindrical P4VP-HABA nanodomains surrounded by the PS matrix. 

Fig. 5. Supramolecular assembly to form ordered structures due to coordination between pyridine-containing chains and silver cations. Adapted from J.-M. Lehn, Supramolecular Chemistry. VCH, Weinheim, 1995.

Fig. 1.2 Thin polymer nanolibers produced by supramolecular assembly of polystyrene-polyvinyl pyridine diblock copolymer PS-f>-P4VP with 4-pentadecylphenol (PDP) after solvent extraction of PDP visualized by AEM. Shown area is 2.5 x 2.5 pm (reproduced from Ref. [38] with permission from Wiley-VCH)...

Another interesting example is the 4 1 piroxicam fumaric acid cocrystal, where the piroxicam is present as both tautomers in the sohd state (Scheme 13.18). Only the nonionized tautomers are hydrogen bonded to fumaric acid, whereas the zwitterionic tautomers aggregate in supramolecular dimers over the protonated pyridine donors and oxo acceptors. Two types of supramolecular assemblies interact through complex network of C-H- O hydrogen bond interactions. 

The reaction of Ag(I)-dimer 11a with the 4-pyridine capped 7r-conjugated ho-modipotic linkers 34 and 35 (Scheme 11.12) afforded the supramolecular assemblies 36a and 37a, respectively, that were characterized by single-crystal X-ray diffraction study (Fig. 11.15) [114, 115]. In these new Tu-stacked supramolecular rectangles two Ag (3a)2 dimers are connected by two Tu-linkers via coordination of their pyridyl termini. The tetracoordinated Ag metal centres in these assemblies exhibit a distorted tetrahedral coordination sphere that has clearly necessitated a profound reorganisation of the metal coordination sphere during the self-assembly process [114]. Therefore, 7i-stacked supramolecular rectangles can be obtained... 

Some related examples with BR2 monocapped ligands are also known [181] and one of these molecules, 129, assembles to an interesting supramolecular structure, in which the cobalt(III) ions in a methylcobaloxime unit are coordinated to the pyridine residues of the bridging B(py)(OMe) group (Fig. 34). The dinuclear complex forms a large rectangular cage that is limited by the two pyridine residues and the cobaloxime moieties. The two pyridine... 

Fig. 34. Compound 129 assembles to a supramolecular structure through coordinative bonds between the cobalt(III) ions and the pyridine residues of the bridging B(py)(OMe) group...

A review13 with 53 references of the transition-metal mediated supramolecular self-assembly is presented. Focus is on the self-assembly of macrocycles, catenanes, and cages from (en)Pd(N03)2 and pyridine-based bridging ligands. 

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