Supramolecular solid materials

Heterogeneous Molecular Recognition. Supramolecular Solid Materials... 

A new field of application is the use of zeolites as templates for generating supramolecular solid materials, e.g. as biomimetic oxygen carriers [14] or photosynthetic systems [15]. The pore structure controls the access of substrates to the active sites closely related to... 

In the field of porous supramolecular metal complexes, both molecular and extended-solid materials have been extensively studied in recent years. A particularly well-studied class of compounds is the metal-containing molecular squares, that is, square-shaped porous tetrameric structures (30,108). These have been prepared by several approaches, the most common being the reaction of an organic bridging ligand with a metal complex that has available cis-coordination sites (109-113) (Fig. 13). However, the resulting metal centers are usually coordinatively saturated, which makes it difficult for guest molecules to interact directly with the metal atoms. 

A second class of monolayers based on van der Waal s interactions within the monolayer and chemisorption (in contrast with physisorption in the case of LB films) on a solid substrate are self-assembled monolayers (SAMs). SAMs are well-ordered layers, one molecule thick, that form spontaneously by the reaction of molecules, typically substituted-alkyl chains, with the surface of solid materials (193—195). A wide variety of SAM-based supramolecular structures have been generated and used as functional components of materials systems in a wide range of technological applications ranging from nanolithography (196,197) to chemical sensing (198—201). 

A lower level of organization in the supramolecular structure is evident even if the layered structure of the core and the stacking of the cyclohexane residues are retained. In this context, ordered H-bonded ionic triple-stranded helicates, involving (R,R)-frdicarboxylic acid, (R,R)-44, in D2O afforded the complex (R.R)-29 (R,R)-44 as large, colourless crystals suitable for X-ray analysis (Scheme 20). The same reaction performed in the presence of the mismatched (5,5)-tra -cyclohexane-l,2-dicarboxylic acid (45) did not give any solid material. A similar result was obtained with (S)-methylsuccinic acid. 

Comparisons of solution and solid-state NMR spectra as well as NMR spectra from solid supramolecular assemblies and single crystals allowed the exact determination of four conformations of iV-octyl-gluconamide in three solid materials, namely monolayer single crystals, bilayer racemate microcrystals, and D-enantiomer bilayer quadruple helices as well as in DMSO solution (Fig. 4.2.6, inserts) (Svenson et al., 1994a). 

The construction of novel coordination polymers is a current interest in the field of supramolecular chemistry and crystal engineering, stemming from their potential applications as frinctional materials as well as their intriguing variety of architectures and molecular topologies. In particular, solid materials with either helical or chiral structures are of intense interest in chemistry and material science. Although solid materials with imusual structures are expected to increase in number, the exploration for preparing framework solids with chiral structures still remains a challenge. Thermal analysis is a fundamental tool for the characterization of these new coordination polymeric compounds. 

Some formally square four-coordinate structures are also fiuxional.Rearrangement of metal clusters and carbonyls which are bound to them have also been studied extensively.DNMR is not limited to solutions and can also be studied in solid materials. DNMR has also been observed with supramolecular complexes.Calixarene complexes based on Ir(l) and Rh(l) complexes also show dynamic motions associated with encapsulation of other molecules. " Although not an organometaiiic, a study of ring inversion in Fe(lll) porphyrins provides a particularly well-documented discussion of the methodologies that can be applied to DNMR. ... 

Cholesterol is essential to life. The name originates from the Greek chole (bUe) and stereos (solid) as cholesterol was first isolated in the solid form from gallstones in 1784. More than 200 years later, it is now well established that important biological functions and solubility properties of cholesterol are intimately linked [12]. Indeed its insolubihty in water explains why this molecule is an important component of the hpid membranes of animal cells. It is this very property that makes cholesterol deleterious, if not lethal. Indeed its deposition within the waU of an artery can lead to the formation of arteriosclerotic plaques. Remarkably these are also the imique self-aggregation properties of cholesterol derivatives that were at the heart of the discovery in 1888 of a new state of matter, the Uquid crystal [13]. In many respects, cholesterol is a fascinating molecule a imique molecular building-block that has been widely exploited in supramolecular and materials chemistry [14-17]. 

---