Molecular polyhedra

Molecular structure of the tetrahedral Fe(II) host-guest complex cation. The capping BF groups and the phenyl rings of the tripod ligands have been omitted for clarity. From S. Mann, G. Huttner, 

The cyanometalate box Cs c [Cp Rh(CN)3]4[Mo(CO)3]4 3 is formed in low yield from the reaction of [Cp Rh(CN)3] (Cp = CsMes) and (/ -CeHtMet )Mo(CO)3 in the presence of cesium ions, and it can be crystallized as a Et4N+ salt. The Cs+ ion serves as a template in the self-assembly of the anionic molecular box, which has a cubic Rh4Mo4(/r-CN)i2 core with three exterior carbonyl ligands attached to each Mo and a Cp group to each Rh. The encapsulated Cs+ ion has a formal coordination number of 12 if interaction with the centers of cyano groups is considered (Fig. 20.3.15). 

Synthesis and structure of the LagLg cluster. Only one ligand is shown, and the coordinating DMSO moleclues have been omitted for 

The super-adamantoid core of the [Ag6(triphos)4(CF3SO )4]2+ cage. The broken lines indicate one of the two adamantane cores formed by silver ions and triflate ligands, whose F atoms have been omitted for clarity. From S. L. James, D. M. P. Mingos, A. J. P. White and D. Williams, Chem Commun., 2323-4 (2000). 

Useful chemical reactions have been carried out in the nano-sized cavity, as illustrated by the in situ isolation of a labile cyclic siloxane trimer (Fig. 20.3.19). In the first step, three to four molecules of phenyltrimethoxysilane enter the cage and are hydrolyzed to siloxane molecules. Next, condensation takes place in the confined environment to generate the cyclic trimer SiPh(0H)0- 3, which is trapped and stabilized in a pure form. The overall reaction yields an inclusion complex [ SiPh(0H)0- 3 c Pt(bipy) 6L4](N03)i2-7H20, which can be crystallized from aqueous solution in 92% yield. The all-cis configuration of the cyclic siloxane trimer and the structure of the inclusion complex have been determined by NMR and ESI-MS. 

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Auguste Bravais (1811-1863) first proposed the Miller-Bravais system for indices. Also, as a result of his analyses of the external forms of crystals, he proposed the 14 possible space lattices in 1848. His Etudes Cristallographiques, published in 1866, after his death, treated the geometry of molecular polyhedra. 

Self-assembly methodologies have been used for the designed synthesis of a range of discrete, metallocyclic 2-D and 3-D coordination compounds. The topologies of many such compounds resemble well-known geometric shapes, so that they are widely referred to as molecular polygons (2-D) or molecular polyhedra (3-D). 

Current interest in metal cluster compounds has arisen from the demonstration that metal-metal bonds play a key role in determining the chemistry of large classes of compounds, in particular, those with heavy metal atoms in low valent states. The occurrence of metal-metal bonding in transition metal complexes has been surveyed 21, 26, 59, 271, 275), and the criteria for metal-metal bonding and the factors contributing to the stability of such bonds have been discussed. Schafer and Schnering Sll) and more recently Keppert and Vrieze 229) have reviewed the lower halide, oxide, and oxyhalide clusters of the heavier transition metals. Cotton 102) has considered the transition metal clusters in terms of structural types, and a similar approach has been adopted in a review of molecular polyhedra of high coordination number 309). 

This section examines several representative, self-assembled 3-D molecular polyhedra in terms of their topological properties. The intention of this work is to (i) illustrate the application of topology to self-assembled molecular polyhedra (ii) provide some pertinent examples to illustrate the concepts and (iii) describe a method of recognizing possible topological transformations in this field. 

Most multinuclear molecular polyhedra have metal ions at the vertices and ligands on the edges of the structure. However, increasing numbers of face-occupied polyhedral assernblies are being reported. One example is shown in Scheme 2, which depicts the reaction of Ti( OPr)4 with the tritopic ligand (2) to generate the face-occupied, T-symmetric assembly [714(2)4] ... 

The capacity of molecular polyhedra to be face- or edge-occupied can complicate their classification when the distinction between an edge, a corner, and a face is not absolute. An example of such a problem involves the neutral complex [Cui2(3)g] (Scheme 3), which is formed by... 

The assembly descriptor method of classifying molecular polyhedra allows a ready comparison of the stoichiometry and topicity of the building blocks in assemblies having widely different... 

Figure 1.13 The 2,3 bipartite graph top-rep describing isomerization of four-vertex molecular polyhedra in which the sites marked Td and correspond to tetrahedral and square planar isomers, respectively. The isomers corresponding to the vertices of the K2 3 bipartite graph are depicted next to the vertex labels.

The formation of radiation defects under irradiation of the fullerene films by the bombarding particles leads to the essential modification of electronic subsystem, which determines their optical and electrophysical properties. However, the mechanisms of radiation defect formation with the use of different types of irradiation and dose load, and also the nature of a change in the electronic properties in this case are studied insufficiently. It is necessary to note that in the case of the condensed state of fullerenes not only the radiation damages of the molecular polyhedrons, which by themselves influence the redistribution of... 

WebLab Viewer gives a very-high-quality display suitable for publication and presentation. Molecules can be displayed as lines, sticks, ball and stick, CPK, and polyhedrons. In addition, different atoms within the same structure may be displayed in different ways. Text can be added to the display as well as labeling parts of the structure in a variety of ways. The user has control over colors, radii, and display quality. The program can also replicate a unit cell to display a crystal structure. Several types of molecular surfaces can be displayed. 

Verdaguer, M. Polyhedron 2001, 20, 1115-1128. A special thematic issue on molecular magnetism. 

E. C. Constable and S. Mundwiler, Metal-ion control of molecular recognition-sugar-functionalised 2,2 6, 2"-terpyridines, Polyhedron, 18 (1999) 2433-2444. 

E. C. Constable, B. Kariuki, and A. Mahmood, New approaches to sugar-functionalised 2,2 6, 2"-terpyridines based upon tetrafluorophenoxy spacers crystal and molecular structures of 4 -(tetrafluoro-4-hydroxyphenyl)-2,2 6, 2"-terpyridine and 4 -(4-methoxytetrafluorophenyl)-2, 2 6, 2" -terpyridine, Polyhedron, 22 (2003) 687-698. 

Figure 4.6 Relationships of idealized sd -1 -hybridized ML molecular shapes to simple polyhedra. Each panel shows the hybrid-orbital axes in dumbbell dz2 -like form embedded within the polyhedron, together with the associated allowed (no-hms-vertex) dispositions of ligands on the polyhedral vertices (with the unmarked metal atom occupying the polyhedral centroid in each case) (a) sd1 square, (b) sd2 octahedron, (c) sd3 cube, and (d) sd5 icosahedron.

A conglomerate of three hexagons contains one central atom and 12 atoms around it. A conglomerate of seven hexahedrons comprises 12 external and 12 internal (common) atoms. In these two cases geometric centers of hybridized molecular orbitals of each hexahedron are equidistant from such nearest centers of a conglomerate. This, apparently, explains the experimental fact that polyhedrons of carbon clusters represent an icosahedron - 12-apex crystalline structure each apex of which is connected with five other apexes. 

We have recently demonstrated the ability of six resorcin[4]arenes and eight water molecules to assemble in apolar media to form a spherical molecular assembly which conforms to a snub cube (Fig. 9.3). [10] The shell consists of 24 asymmetric units - each resorcin[4]arene lies on a four-fold rotation axis and each H2O molecule on a three-fold axis - in which the vertices of the square faces of the polyhedron correspond to the corners of the resorcin[4]arenes and the centroids of the eight triangles that adjoin three squares correspond to the water molecules. The assembly, which exhibits an external diameter of 2.4 nm, possesses an internal volume of about 1.4 A3 and is held together by 60 O-H O hydrogen bonds. 

King RB (1976) In Liebman JF, Greenberg A (eds) Molecular structure and energetics. VCH, Deerfield Beach, Florida, pp 123-148 Stone AJ (1981) Inorg Chem 20 563 Stone AJ (1980) Mol Phys 41 1339 Stone AJ, Alderton MJ (1982) Inorg Chem 21 2297 Stone AJ (1984) Polyhedron 3 1299... 

Sharma and Reed, 1976)]. In proteins the coordination number 4 is most common, where the zinc ion is typically coordinated in tetrahedral or distorted tetrahedral fashion. The coordination polyhedron of structural zinc is dominated by cysteine thiolates, and the metal ion is typically sequestered from solvent by its molecular environment the coordination polyhedron of catalytic zinc is dominated by histidine ligands, and the metal ion is exposed to bulk solvent and typically binds a solvent molecule (Vallee and Auld, 1990). The inner-sphere coordination number of catalytic zinc may increase to 5 during the course of enzymatic turnover, and several five-coordinate zinc enzyme—substrate, enzyme product, and enzyme-inhibitor complexes have been studied by high-resolution X-ray crystallographic methods (reviewed by Matthews, 1988 Christianson and Lipscomb, 1989). The coordination polyhedron of zinc in five coordinate examples may tend toward either trigonal bipyramid or octahedral-minus-one geometry. 

The p3-bridged carbonato complex posseses a pseudo-3-fold molecular symmetry. Each of the Cu atoms is five coordinate with the four nitrogen atoms of tren and one oxygen atom of the carbonate ligand (C). The coordination polyhedron of the Cu atom can be described as almost (TBP), the copper ions being slightly out of the plane (0.15 A) of the three primary amine groups (Fig. 5). 

Gosed polyhedral structure with triangular faces only known only as with molecular formula (B HJ2- ( + I skeletal electron-pairs for polyhedron. 

Nest-like, nonclosed polyhedral structure molecular formula B H + 4 ( + 2) skeletal electron-pairs n vertices of the parent (n + l)-atom c/oro-polyhedron occupied. 

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