Metal-Ligand Polyhedra

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Contents 1 M24L48 Polyhedron (26 Faces) 2 Ligand Angle vs. Polyhedron Size 3 Significance 4 References and Notes 5 Models

M24L48 Polyhedron (26 Faces)

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Metal ions with square planar coordination, when mixed with suitable 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 Size

The dipyridylthiphene ligand pictured above has a bend angle of 127^o[2]

Significance

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References and Notes

1. ↑ Coxeter, H. S. M., Regular Polytopes, Dover Publications, New York, 3rd ed., 1973.
2. ↑ ^{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
3. ↑ 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.

Models

• M24L48 main chain atoms only: Image:M24L48 main chains.pdb
  • View in FirstGlance in Jmol
• M24L48 all atoms: Image:M24l48-single-polyhedron.pdb
  • View in FirstGlance in Jmol