Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-05-01
2002-04-16
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S148000, C556S150000, C534S015000
Reexamination Certificate
active
06372932
ABSTRACT:
This invention relates to solid products which are both porous and chiral, by virtue of an absence of symmetry of a crystal structure of the atoms and molecules with its mirror image, involving reflection or inversion.
The search for porous chiral solids is driven largely by a desire to perform enantioselective separations and syntheses, processes which are of fundamental importance to the pharmaceuticals industry. Solid materials currently used to perform enantioseparations include natural and synthetic polymers, chiral sorbents and chiral membranes. Parallel with the search for solids is the synthesis of solution species for homogeneous catalysis and molecular recognition.
Yaghi O M et al (J Am. Chem. Soc. (1996) 118(38),9096-9101; Nature (London) (1995), 378, (6558), 703-6; and U.S. Pat. No. 5,648,508) describe microporous materials which comprise for example chains or 2-dimensional nets of complexes of 1,3,5-benzenetricarboxylate with metal ions, said chains or nets being held together by hydrogen bonding or other specific interaction.
According to the present invention there is provided a porous chiral solid product which comprises two or more interpenetrating chiral (10, 3)-a networks of 1,3,5-benzenetricarboxylate molecules
where X is H, hydrocarbon, halide, etc, linked through metal atoms. (10, 3)-a networks are structures containing 10-sided loops constructed with triangular connectors, as described by Wells. “Structural Inorganic Chemistry”, 4
th
Ed., Clarendon Press, Oxford, 1975 and “Three-Dimensional Nets and Polyhedra”, Wiley-lnterscience, NY, 1977.
The solid product is an infinite molecular coordination network. The compounds described below are the only known infinite molecular coordination networks to be both chiral and porous, and are among only a handful of solids known to have both of these properties. These solid products contain three metal atoms for every two 1,3,5-benzenetricarboxylate molecules.
In the structural formula shown above, the groups X may be the same or different at different locations of the molecule. The nature of the group X is not specially critical. Preferably they are inert groups small enough not to cause steric hindrance such as lower (C
1
-C
5
) aliphatic groups or I, Br, Cl or F or particularly hydrogen atoms.
Preferably each metal atom acts as a linear connector between two 1,3,5-benzenetricarboxylate molecules. Preferably the metal is a transition or lanthanide metal having a coordination greater than 2. Preferably each metal atom (linking two 1,3,5-benzenetricarboxylate molecules) also carries one or more coordinated ligands. These ligands may be mono- or poly-dentate, and promising examples include alcohols, thiols, water, ammonia, aliphatic and aromatic amines and amides, halides, carboxylates, oxalate, nitrate, nitrite, sulfate, phosphate, oxide, sulfide, cyanide and thiocyanate. In desolvated salts (obtained by heating) it is not essential for all coordination sites of the metal atom to be satisfied by a coordinating ligand.
The metal atoms should preferably carry additional ligands that favour the linear coordination of the 1,3,5-benzenetricarboxylate and which satisfy the coordination environment of the metal. Although the binding of some ligands such as alcohols does in effect stabilise the structure by hydrogen-bonding, it is primarily the favourable energetics of formation of the structure, rather than the stability once it has formed that is important. Indeed, once formed, it is highly probable that heating the materials may liberate some of the bound ligands without destroying the framework structure.
When the metal has an oxidation state of 2, and these ligands are not electrically charged, then the solid product is electrically neutral. Alternatively if the metal atoms are in an oxidation state greater than or less than 2; and/or one or more of the ligands is electrically charged, then the whole molecular coordination network may be cationic or anionic. This may confer useful properties as described in more detail below.
The solid product may consist of four (10, 3)-a networks. Alternatively the solid product may consist of less than four such interpenetrating networks, and this may increase the solvent accessible volume of the product.
The solid product of the invention may be made by providing a solution of a metal salt, e.g. a transition or lanthanide metal salt, and a 1,3,5-benzenetricarboxylate as defined above, in a solvent consisting of one or more ligands for the chosen metal. Preferably the solution contains substantially three metal atoms for every two 1,3,5-benzenetricarboxylate molecules (btc). The desired product is recovered as a crystalline solid from the solution. Although each crystal is enantiomerically pure, the polycrystalline product may be a racemic mixture of crystals. While such a racemic mixture is useful for many of the purposes described below, it may be preferable to make an enantiomerically pure product, and this may be achieved either by using a chiral ligand for the metal, by forming the solid about a chiral template, by seeding crystal growth from a single enantiomeric crystal, by crystallising in the presence of a chiral cosolute, or by selective nucleation on a chiral surface.
The solid products of this invention have a number of features that make them promising for both chemical and physical application. Porous framework solids have several chemical uses, ranging from heterogeneous catalysis to molecular (neutral molecule, cation or anion) recognition and exchange. Forseeable chemical applications of the chiral (10, 3)-a network materials of btc include use
(a) as catalysts that show stereo- and enantio-selectivity to reactants, products and transition-species,
(b) as selective adsorbants, able to remove small components from reaction mixtures (and thereby influence reaction equilibria), to remove unwanted species from liquid or gaseous media (e.g. the removal of toxins from the environment), or to act as chromatographic phases for the separation of isomers and enantiomers,
(c) as detectors in either the liquid or gaseous phase,
(d) as hosts for reactive agents or biologically important molecules, enabling controlled release by diffusion,
(e) as ion-exchange lattices.
The inclusion and physical manipulation of nanoparticle hosts in the cavities of porous solids opens up a range of physical applications, such as data storage and quantum electronics. Framework solids in many cases show unusual and useful mechanical properties, including structural hysteresis, negative coefficients of thermal expansion, and auxetic behaviour (negative Poisson's ratio). Finally, chiral solids find many applications which utilise their piezoelectric and optical rotatory properties.
Several porous chiral (10, 3)-a networks based on 1,3,5-benzenetricarboxylates have been characterised structurally. It is thought that a large and diverse family of materials with the same chiral framework structure may be synthesised. Notable differences between the structurally characterised materials support this claim: the structures form in different crystal systems (cubic and tetragonal), the coordination around the metal atom differs, the shapes of the pores differ considerably, and the solvent molecules occupying the cavities are different in each. The important and defining feature in the proposed family of salts is that a metal atom acts as a linear connector between two 1,3,5-benzenetricarboxylate anions, and that the planes of these anions are able to lie approximately orthogonal to each other (at 109.47° for a perfectly regular cubic (10, 3)-a network).
REFERENCES:
patent: 5648508 (1997-07-01), Yaghi
Kepert et al, “A porous chiral framework of coordinated . . . ,” Chem. Commun., 00. 31-32 (1998).
Yaghi et al, “Construction of Porous Solids from Hydrogen-Bonded Metal . . . ,” J. Am. Chem. Soc., vol. 118, pp. 9096-9101 (1996).
Yaghi et al, “Selective binding and removal of guestsin a microporous metal-organic framework,” Nature (Letters to Nature), vol. 378, pp. 703-706 (1995).
Kepert Cameron J
Rosseinsky Matthew J
Nixon & Vanderhye
University of Liverpool
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