Tetrahedra, distorted

For the coordination number 4 three types of polyhedra have to be considered a tetrahedron (distorted), a tetragonal pyramide, and a closely related T-trigonal bipyramide. 

Walsh diagram at the extended Huckel level for the square planar to tetrahedron distortion in NiH4. 

Methane, CH4, for example, has a central carbon atom bonded to four hydrogen atoms and the shape is a regular tetrahedron with a H—C—H bond angle of 109°28, exactly that calculated. Electrons in a lone pair , a pair of electrons not used in bonding, occupy a larger fraction of space adjacent to their parent atom since they are under the influence of one nucleus, unlike bonding pairs of electrons which are under the influence of two nuclei. Thus, whenever a lone pair is present some distortion of the essential shape occurs. 

Addition of halide ions to aqueous copper(II) solutions can give a variety of halo-complexes for example [CuCl4] (yellow square-planar, but in crystals with large cations becomes a flattened tetrahedron) [CuClj] (red, units linked together in crystals to give tetrahedral or distorted octahedral coordination around each copper). 

Phosphoms oxychloride has strong donor properties toward metal ions. The remarkably stable POCl —AlCl complex has been utilized to remove AlCl from Friedel-Crafts reaction products. Any POX molecule contains a pyramidal PX group the oxygen atom occupies the fourth position to complete the distorted tetrahedron (37). Some properties of phosphoms oxyhaUdes ate presented in Table 8. 

The structure of the low-temperature modification of the compound, Na2Ta205F2 (I), has not yet been determined. The high-temperature modification, Na2Ta205F2 (II), can be conceived as two sub-lattices Tai6X52, which is composed of TaX6 octahedrons and Na Xt, which contains Na X2 tetrahedrons [192]. Fig. 38 shows the structure of Na2Ta205F2 (II). Two additional sodium atoms occupy the centers of two bi-pyramids with distorted hexagonal bases. 

Fig. 17. Tetragonal symmetry projective view (above) and cut A-B (below) of a [LS],-layer formed by a sequence of [L,S] tetrahedrons (ideally PbFCl-t3q)e distorted CeSI-, FeOCl-, and NdSBr-types). (Redrawn from C. Dagron and F. Thevet, Ann. Ckim. 6, 67 (1971), Fig. 6, p. 77.)...

The telluride halides crystallize in monoclinic lattices, but only In-TeBr and InTel are isotypic 162). InTeCl forms a layer type of structure, as do InSCl and its analogs, but, owing to the size of the Te atom and the enhanced covalency of the In-Te bond, only a coordination number of 4 for indium is realized. The structure is built up of strongly distorted, InTesraCli/j tetrahedra that share the corners and edges occupied by Te atoms. The Cl atoms are coordinated to one tetrahedron each, and do not take part in the layer formation 324, 325). 

The simplest iron-sulfur centers, which were first discovered in ru-bredoxins, consist of one iron ion coordinated by a distorted tetrahedron of cysteinyl sulfur atoms. This environment provides a weak ligand field giving a spin equal to and 2 when the ion is Fe(III) and Fe(II), respectively. It also determines the splitting of the ground spin manifold, and consequently the characteristics of the EPR spectrum. This splitting is generally described in the framework of the spin Hamiltonian ... 

Presently it is not possible to relax the Cu lattice at the SCF level, since from a computational point of view it is composed of two different kinds of Cu atoms (those with and without the ECP). Also questions of wetting, i.e. whether the chemisorbed Be4 would prefer to remain as a tetrahedron (or distorted tetrahedron) or to spread out to a single layer are still not amenable to ab initio study. These questions have not yet been investigated using the parameterized model approach, because of the problems associated with modeling Be2 and Beg as accurately as larger Be clusters. Nonetheless, these preliminary results show that the parameterized and ab initio calculations can be used to complement each other in a multicomponent system, just as for single component systems. 

The structure of ice. (a) Each oxygen atom is at the center of a distorted tetrahedron of hydrogen atoms. The tetrahedron is composed of two short covalent O—H bonds and two long H—O hydrogen bonds, (b) Water molecules are held in a network of these tetrahedra. 

Hydrogen bonding in solid ice creates a three-dimensional network that puts each oxygen atom at the center of a distorted tetrahedron. Figure 11-16 shows that two arms of the tetrahedron are regular covalent O—H bonds, whereas the other two arms of the tetrahedron are hydrogen bonds to two different water molecules. 

The reaction of metallic copper with thiuram disulfides yields complexes of Cu I), which are polymeric in solution as well as in the solid state 121,122). In 123) the copper atoms are located at the corners of a slightly distorted tetrahedron with Cu—Cu distances ranging from 2.6—2.7 A. Each of the copper atoms is coordinated to three sulfur atoms in a nearly planar triangular arrangement and each sulfur atom coordinates one or two copper atoms. 

W(VI) compounds with 5cP electronic configuration, the EFG is reasonably weU described by the lattice contribution only. The regular octahedral WOs structure yields zero EFG in agreement with experiment, while the deformed tetrahedral W04 strucmre results in significant quadrupole coupling constants of either sign, e Q > 0 and also <0, depending on the distortion of the O4 tetrahedron. 

The crystal structures of many organolithium compounds have been determined.44 Phenyllithium has been crystallized as an ether solvate. The structure is tetrameric with lithium and carbon atoms at alternating corners of a highly distorted cube. The lithium atoms form a tetrahedron and the carbons are associated with the faces of the tetrahedron. Each carbon is 2.33 A from the three neighboring lithium atoms and an ether molecule is coordinated to each lithium atom. Figures 7.2a and b show, respectively, the Li-C cluster and the complete array of atoms, except for hydrogen 45 Section 6.2 of Part A provides additional information on the structure of organolithium compounds. 

If the t2 orbitals are occupied unevenly, Jahn-Teller distortions occur. For configuration d4, one of the t2 orbitals is unoccupied for d9, one has single occupation and the rest double. As a consequence, the ligands experience differing repulsions, and a flattened tetrahedron results (Fig. 9.2). Typical bond angles are, for example in the CuCl4 ion, 2x 116° and 4 x 106°. 

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