Metal-Ligand Polyhedra: Difference between revisions
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==Significance== | ==Significance== | ||
Metal-ligand polyhedra could serve as nanoreactors containing a chemically defined nano-environment. Similar polyhedra have been constructed from ligands with covalent adducts facing the interior. Specifically, 24 perfluoroalkyl chains have been caged in an M12L24 polyhedron, forming a fluorous phase potentially useful for separation, purification, or reaction control in organic syntheses<ref>PMID: 16946067</ref>. In addition, the surfaces of such polyhedra have been decorated with attached groups. Photoresponsive nanoparticles have been demonstrated<ref>PMID: 20508119</ref>. | |||
More generally, self-assembly of metal-ligand polyhedra demonstrates emergent behavior, in which microscopic differences lead to macroscopic differences. Such self-assembly is reminiscent of the assembly of virus capsids and other biological structures. | |||
==References and Notes== | ==References and Notes== | ||
Revision as of 03:01, 14 June 2010
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M24L48 Polyhedron (26 Faces)M24L48 Polyhedron (26 Faces)
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Metal ions with square planar coordination, when mixed with bent bidentate ligands, can self-assemble into polyhedra of various sizes. Geometrical constraints limit the number of metal ions (vertices) to 6, 12, 24, 30, or 60 for entropically favored regular or semiregular polyhedra[1]. Shown at right () is the "main chain" of a crystallographic model for the largest such structure reported as of May, 2010[2]. form the vertices of a 26-face polyhedron[3]. Three square faces and one triangular face meet at each vertex.
Each palladium ion is coordinated by . The nitrogens are bridged by a ("ligand"). There are two ligand molecules (L) per metal ion (M); hence, this structure is called M24L48.
The models shown thus far are simplified, including only the "main chain". The actual M24L48 complex analyzed crystallographically contained a substituent of -OCH2CH2O- on each thiophene ring, PF6- counterions bound to the surface of the polyhedron, and hydrogen atoms. Here is the (but lacking the three additional nitrogens coordinating each palladium, and water, which was not resolved crystallographically). Here is the (but lacking PF6 and water).
Ligand Angle vs. Polyhedron SizeLigand Angle vs. Polyhedron Size
The dipyridylthiphene ligand pictured above, in the M24L48 polyhedron, has a bend angle of 149o[2]. A ligand with a sharper bend of 129o (dipyridylfuran[4]) forms a smaller polyhedron, M12L24[5]. A ligand with an even sharper bend of 90o forms M6L12[6].
SignificanceSignificance
Metal-ligand polyhedra could serve as nanoreactors containing a chemically defined nano-environment. Similar polyhedra have been constructed from ligands with covalent adducts facing the interior. Specifically, 24 perfluoroalkyl chains have been caged in an M12L24 polyhedron, forming a fluorous phase potentially useful for separation, purification, or reaction control in organic syntheses[7]. In addition, the surfaces of such polyhedra have been decorated with attached groups. Photoresponsive nanoparticles have been demonstrated[8].
More generally, self-assembly of metal-ligand polyhedra demonstrates emergent behavior, in which microscopic differences lead to macroscopic differences. Such self-assembly is reminiscent of the assembly of virus capsids and other biological structures.
References and NotesReferences and Notes
- ↑ Coxeter, H. S. M., Regular Polytopes, Dover Publications, New York, 3rd ed., 1973.
- ↑ 2.0 2.1 Sun QF, Iwasa J, Ogawa D, Ishido Y, Sato S, Ozeki T, Sei Y, Yamaguchi K, Fujita M. Self-assembled M24L48 polyhedra and their sharp structural switch upon subtle ligand variation. Science. 2010 May 28;328(5982):1144-7. Epub 2010 Apr 29. PMID:20430973 doi:10.1126/science.1188605
- ↑ M24L48 forms a 26-faced rhombicubooctahedron with 18 square faces and 8 triangular faces. In this instance, the rectangular faces are very close to squares 13.35 Ångstroms on a side.
- ↑ Dipyridylfuran differs from dipyridylthiophene in that oxygen replaces the sulfur.
- ↑ Tominaga M, Suzuki K, Kawano M, Kusukawa T, Ozeki T, Sakamoto S, Yamaguchi K, Fujita M. Finite, spherical coordination networks that self-organize from 36 small components. Angew Chem Int Ed Engl. 2004 Oct 25;43(42):5621-5. PMID:15455450 doi:10.1002/anie.200461422
- ↑ Suzuki K, Tominaga M, Kawano M, Fujita M. Self-assembly of an M6L12 coordination cube. Chem Commun (Camb). 2009 Apr 7;(13):1638-40. Epub 2009 Feb 17. PMID:19294246 doi:10.1039/b822311d
- ↑ Sato S, Iida J, Suzuki K, Kawano M, Ozeki T, Fujita M. Fluorous nanodroplets structurally confined in an organopalladium sphere. Science. 2006 Sep 1;313(5791):1273-6. PMID:16946067 doi:313/5791/1273
- ↑ Stefankiewicz AR, Sanders JK. Chemistry. Harmony of the self-assembled spheres. Science. 2010 May 28;328(5982):1115-6. PMID:20508119 doi:328/5982/1115
ModelsModels
- M24L48 main chain atoms only: File:M24L48 main chains.pdb
- M24L48 all atoms: File:M24l48-single-polyhedron.pdb