Molecular crystal, two-component

Keywords acridine, diphenylacetic acid, photodecarboxylation, two-component molecular crystal, chiral crystal, 7,8-dihydro-7-diphenylmethyl-acridine... 

Chiral crystals generated from non-chiral molecules have served as reactants for the performance of so-called absolute asymmetric synthesis. The chiral environments of such crystals exert asymmetric induction in photochemical, thermal and heterogeneous reactions [41]. Early reports on successful absolute asymmetric synthesis include the y-ray-induced isotactic polymerization of frans-frans-l,3-pentadiene in an all-frans perhydropheny-lene crystal by Farina et al. [42] and the gas-solid asymmetric bromination ofpjp -chmethyl chalcone, yielding the chiral dibromo compound, by Penzien and Schmidt [43]. These studies were followed by the 2n + 2n photodimerization reactions of non-chiral dienes, resulting in the formation of chiral cyclobutanes [44-48]. In recent years more than a dozen such syntheses have been reported. They include unimolecular di- r-methane rearrangements and the Nourish Type II photoreactions [49] of an achiral oxo- [50] and athio-amide [51] into optically active /Mactams, photo-isomerization of alkyl-cobalt complexes [52], asymmetric synthesis of two-component molecular crystals composed from achiral molecules [53] and, more recently, the conversion of non-chiral aldehydes into homochiral alcohols [54,55]. 

Decarbonylation and Decarboxylation - The photochemical reactions between carboxylic acids such as formic and trifluoroacetic acid and silica surfaces have been studied. The irradiation of diphenylacetic acid in acetonitrile with acridine results in the decarboxylation and the formation of the adduct (102). When the two achiral compounds, acridine and diphenylacetic acid, are cocrystallized a chiral two component molecular crystal is obtained in which the components are present in a 1 1 ratio. Both (—)- and (+)- crystals can be obtained. This crystalline material is photochemically reactive and irradiation brings about decarboxylation and formation of the adduct (102) with an ee of 35%. This compound is accompanied by a low yield of (103) which is formed exclusively on irradiation of the reactants in acetonitrile solution.Photochemical decarboxylation can be brought about by the irradiation of benzilate (104)/ methyl viologen pairs. ... 

When the intermolecular forces are relatively strong and directional, crystalline molecular compounds (crystalline molecular complexes) are formed. They have fixed stoichiometries and ordered structures. These two-component molecular crystals are also called cocrystals or maybe adduct crystals. Hydrogen-bonded cocrystals, donor-acceptor crystals (charge transfer crystals), and inclusion crystals (host-guest crystals) are examples of crystalline molecular complexes. Crystalline organic salt is a special case of hydrogen-bonded cocrystal or donor-acceptor crystal, i.e., proton (or electron) transfer from the acid (or donor) to base (or acceptor) occurred. 

Hydrogen bonding is the most important directional Interaction responsible for supramolecular construction [17], Appendix 1 illustrates several typical hydrogen bond patterns which are present in two-component molecular crystals. Appendix 2 exemplifies a variety of reported cocrystals selected mainly fiom the recent papers [18], Not only strong hydrogen bonds (i.e, 0—H "0, 0—H- N,... 

Vyskocil S, Smrcina M, Lorenc M, Hanus V, Polasek M, Kocovsky P (1998) On the Novel two-phase oxidative cross-coupling of the two-component molecular crystal of 2-naphthol and 2-naphthylamine . Chem Commun 585-586... 

A possible way to induce selectivity in the photodecarboxylation process could be through photosensitized reactions in the soHd state. In fact, when a two-component molecular crystal of phenanthridine and 3-indoleacetic acid is irradiated at low temperature (-70°C), 3-methyHndole is formed in high yield as the sole product by contrast, when the same reaction is carried out in acetonitrile solution, four products are obtained.Furthermore, irradiation of two-component molecular crystals of arylalkyl carboxylic acids with stoichiometric amounts of electron acceptor causes decarboxylative condensation between the two components with important selectivities. " Thus, irradiation of (S)-naproxen in a chiral crystal with 1,2,4,5-tetracyanobenzene produces a decarboxylated condensation product retaining the initial chirality." Photolysis of an enantiomorphous bimolecular crystal of acridine with the R or S enantiomer of 2-phenylpropionic acid causes stereoselective condensation to give three optically active products. An absolute asymmetric synthesis has also been achieved by the enantioselective decarboxylative condensation of a chiral molecular crystal formed from achiral diphenylacetic acid and acridine (Scheme 9). ... 

Koshima, H., Ding, K., Chisaka, Y., Matsuura, X, Miyahara, I., and Hirotsu, K., Stoichiometrically sensitized decarboxylation occurring in the two-component molecular crystals of aza aromatic compounds and aralkyl carboxylic acids,/. Am. Chem. Soc., 119,10317,1997. 

Solid-state irradiation of two component molecular crystals of thienylacetic acids with aza aromatic compounds (acridine and phenanthridine) ° results in photodecarboxylation and gives decarboxylated and condensation products. Two-component molecular crystals of the above azo aromatic compounds with 3-indolepropionic acid and 1-naphthylacetic acid, upon solid-state irradiation, give radical intermediates via electron transfer and ultimately afford decarboxylated compounds in near quantitative yield. Irradiation of crystalline charge-transfer complexes of 3-indoleacetic acid and 2-naphthylacetic acid with 1,2,4,5-tetracyanobenzene gives methylnaphthalene (decarboxylation) and naphthyl(2,4,5-tricy-ano)methane (dehydrocyanating condensation) in the solid state. 

Koshima, H., Matsushige, D., Miyauchi, M., and Fujita, J., Solid-state photoreaction in two-component molecular crystals of thienylaceticadds and aza aromatic compounds. Tetrahedron, 56, 6845, 2000. 

Sugiyama, J., J. Meng, and T. Matsurra. 2002. Two-component molecular crystals composed of chloronitrobenzoic acids and 4-aminopyridine. Acta Crystallogr. C 58 o242-o246. 

Koshima, H., S. Honke, and J. Fujita. 1999. Generation of chirality in two-component molecular crystals of tryptamine and achiral carboxylic acids. J. Ore. Chem. 64 3916-3921. 

An entirely analogous procedure can be applied to determine the radiative width of exciton states in two-dimensional molecular crystals. In this case an exciton can decay only into a photon, which has an in-plane component of the wavevector equal to the exciton wavevector. Denote this component by ky, and the component perpendicular to the crystal plane by q (q = ky + qj ). Then the probability of decay of an exciton with given wavevector k is equal to... 

The two-component system—crystal lamellae or blocks alternating with amorphous layers which are reinforced by tie molecules— results in a mechanism of mechanical properties which is drastically different from that of low molecular weight solids. In the latter case it is based on crystal defects and grain boundaries. In the former case it depends primarily on the properties and defects of the supercrystalline lattice of lamellae alternating with amorphous surface layers (in spherulitic, transcrystalline or cylindritic structure) or of microfibrils in fibrous structure, and on the presence, number, conformation and spatial distribution of tie molecules. It matters how taut they are, how well they are fixed in the crystal core of the lamellae or in the crystalline blocks of the microfibrils and how easily they can be pulled out of them. In oriented material the orientation of the amorphous component (/,) is a good indicator of the amount of taut tie molecules present and hence an excellent parameter for the description of mechanical properties. In fibrous structure it directly measures the fraction and strength of microfibrils present and therefore turns out to be almost proportional to elastic modulus and strength in the fibre direction. 

The initial configuration is set up by building the field 0(r) for a unit cell first on a small cubic lattice, A = 3 or 5, analogously to a two-component, AB, molecular crystal. The value of the field 0(r) = at the point r = (f, 7, k)h on the lattice is set to 1 if, in the molecular crystal, an atom A is in this place if there is an atom B, 0, is set to —1 if there is an empty place, j is set to 0. Fig. 2 shows the initial configuration used to build the field 0(r) for the simple cubic-phase unit cell. Filled black circles represent atoms of type A and hollow circles represent atoms of type B. In this case all sites are occupied by atoms A or B. 

Here the vector rj represents the centre of mass position, and D is usually averaged over several time origins to to improve statistics. Values for D can be resolved parallel and perpendicular to the director to give two components (D//, Dj ), and actual values are summarised for a range of studies in Table 3 of [45]. Most studies have found diffusion coefficients in the 10 m s range with the ratio D///Dj between 1.59 and 3.73 for calamitic liquid crystals. Yakovenko and co-workers have carried out a detailed study of the reorientational motion in the molecule PCH5 [101]. Their results show that conformational molecular flexibility plays an important role in the dynamics of the molecule. They also show that cage models can be used to fit the reorientational correlation functions of the molecule. 

The isolation of crystalline products having mixed polymorphic compositions (often referred to as concomitant polymorphism) remains a topic of interest, even though the phase rule predicts that a system at equilibrium consisting two components (solvent + solute) and three phases (solution + Form I + Form II) is uni variant. Hence, for crystallizations performed at a fixed pressure (typically atmospheric) the system becomes nonvariant and genuine equilibrium can exist at only one temperature. Therefore, concomitant products must be obtained under nonequilibrium conditions. Flexibility in molecular conformation was attributed to the concomitant polymorphs of a spirobicyclic dione [34] and of 3-acetylcoumarin [35],... 

Almost all the crystalline materials discussed earlier involve only one molecular species. The ramifications for chemical reactions are thereby limited to intramolecular and homomolecular intermolecular reactions. Clearly the scope of solid-state chemistry would be vastly increased if it were possible to incorporate any desired foreign molecule into the crystal of a given substance. Unfortunately, the mutual solubilities of most pairs of molecules in the solid are severely limited (6), and few well-defined solid solutions or mixed crystals have been studied. Such one-phase systems are characterized by a variable composition and by a more or less random occupation of the crystallographic sites by the two components, and are generally based on the crystal structure of one component (or of both, if they are isomorphous). 

It is well known that there are two types of crystal structure in Bionolle (as shown in Fig. 6) [2]. The crystal structures are formed mainly by the major component, PBS. The 1000 series is described here, and the stmctures of the 3000 and 5000 series are the same. Figure 6a shows the crystal stmcture observed from the molecular axis ... 

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