Molecular tetrahedron

Fig. 21 Saalfrank and co-workers reported the formation of the first molecular tetrahedron 30 [144]. Modification of the original tetra-carboxylate ligand 29 allowed the formation of tetrahedron 32 based on ligand 31 [122]...

An example of a molecule that self-assembles to give a finite 3D assembly is triphenylmethanol.32 The alcohol has been shown to self-assemble in the solid state, via O-H-O hydrogen bonds, to form a tetramer, with the point group C3 and a structure that conforms to a molecular tetrahedron (Fig. 14). The hydrogen bonds exhibited substantial dynamic disorder in the solid. Each molecule sits at the corner of the tetrahedron with the phenyl rings in propeller-like conformations. 

Fig. 14 Solid-state structure of the molecular tetrahedron based on triphenylmethanol.

A four-component capsule with a structure that conforms to a tetrahedron has been recently described by Venkataraman66 Specifically, triphenylamine ortho-tricarboxylic acid self-assembled via 12 O H-O hydrogen bonds to form a molecular tetrahedron (Fig. 36). The hydroxyl groups of the polyhedron participated in hydrogen bonds with single ethanol molecules embedded within each triangular face of each tetrahedron. The assembly crystallized in the rare cubic crystal system. The ability of the acid to form a tetrahedron was reminiscent of the ability of triphenyl-methanol to form a tetrahedron, which also forms inclusion compounds with solvent guests that occupy voids between the polyhedra.32... 

The Saalfrank method to produce the first molecular tetrahedron. 

Fig. 5 Self-assembly cf a face-occupied molecular tetrahedron b> the Symmetry Interaction approach (From Ref [28] )...

Description by rotational lists was introduced by Cook and Rohde [110] in the specification of the Standard Molecular Data (SMD) format [111]. In this stereochemical approach, the basic geometrical arrangements around a stcrcoccntcr arc defined in a list (c.g., square, tetrahedron, etc.). The atoms in those stcrcoclcmcnts are also labeled with numbers in a pre-defined way (Figure 2-72),... 

A common application of the direct calculation of molecular energy is the study of organic reaction mechanisms. You can investigate the energies of different potential intermediates, species not easily studied by experiment. A review by Thiel lists many such 39. Thiel, W. Semiempirical Methods Current Status and Perspectives Tetrahedron, 44 7393, 1988. 

Figure 13.17 Molecular structure of some sulfides of arsenic, stressing the relationship to the AS4 tetrahedron (point group symmetry in parentheses).

Recently H. L. Jones and D. L. Beveridge have presented molecular orbital calculations on the electronic structure of 2,3-pyrid5me explaining the exclusive formation of 2-aminopyridine from this intermediate [Tetrahedron Letters No. 24, 1577 (1964)]. 

Zeolite is sometimes called molecular sieve. It has a well defined lattice structure. Its basic building blocks are silica and alumina tetrahedra (pyramids). Each tetrahedron (Figure 3-1) consists of a silicon or aluminum atom at the center of the tetrahedron, with oxygen atoms at the four comers. 

The sculpture shows artistically stacked tetrahedra. The molecular geometry for the molecule CCI4 is that of a tetrahedron. 

We are now ready to account for the bonding in methane. In the promoted, hybridized atom each of the electrons in the four sp3 hybrid orbitals can pair with an electron in a hydrogen ls-orbital. Their overlapping orbitals form four o-bonds that point toward the corners of a tetrahedron (Fig. 3.14). The valence-bond description is now consistent with experimental data on molecular geometry. 

FIGURE 3.16 Three common hybridization schemes shown as outlines of the amplitude of the wavefunction and in terms of the orientations of the hybrid orbitals, (a) An s-orbital and a p-orbital hybridize into two sp hybrid orbitals that >oint in opposite direc tions, forming a linear molecular shape, (b) An s-orbital and two p-orbitals can blend together to give three ip hybrid orbitals that point to the corners of an equilateral triangle, (c) An s-orbital and three p-orbitals can blend together to give four sp hybrid orbitals that point to the corners of a tetrahedron. 

The Li + dication with two electrons AN + 2, N= 0) adopts a tetrahedral structure [42]. The single molecular orbital composed of four i-orbitals at the lowest energy level in the tetrahedron is lower than that in the square. The number of the in-phase relations between the. y-orbitals is greater in the tetrahedron. 

Having introduced methane and the tetrahedron, we now begin a systematic coverage of the VSEPR model and molecular shapes. The valence shell electron pair repulsion model assumes that electron-electron repulsion determines the arrangement of valence electrons around each inner atom. This is accomplished by positioning electron pairs as far apart as possible. Figure 9-12 shows the optimal arrangements for two electron pairs (linear),... 

We cannot generate a tetrahedron by simple overlap of atomic orbitals, because atomic orbitals do not point toward the comers of a tetrahedron. In this section, we present a modification of the localized bond model that accounts for tetrahedral geometry and several other common molecular shapes. 

J. Automatic generation of 3D atomic coordinates for organic molecules. Tetrahedron Comput. Methodol. 1990, 3, 537-547. b) GORINA, Molecular Networks GmbH, Erlangen, Germany, http //www.mol-net.de. 

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