Tetrahedral complexes point group

The chromate anion is a highly soluble, toxic tetrahedral complex (point group Tj) that occurs in oxidized, neutral-basic solutions. It is also one of a small number of aqueous complexes that have been thoroughly characterized by spectroscopic measurements on numerous isotopic compositions (Muller and Kbniger 1974), so it will be possible to check the vibrational model against real data. Here the MUBFF is applied under the assumption that aqueous chromate can be approximately modeled as a gas-phase molecule. 

All halides EX4 form tetrahedral molecules (point group Td). Mixed halides are known, as well as fully or partially halogen-substituted catenated alkanes, silanes and germanes (e.g. Ge2Cl6). Unlike the carbon compounds, halides of Si and Ge are Lewis acids and readily form complexes such as [SiF6]. Attack by Lewis bases often leads to decomposition, and thus rapid hydrolysis in water,... 

As a first illustration let us consider the optical transitions in a tetrahedral complex of Co(II). The ground state belongs to the A2 representation of the tetrahedral point group Td, and there are two excited states of F, symmetry and one of T2 symmetry. The character table for Td tells us that the coordinates x, y, and z form a basis for the T2 representation. For the A2 F, transitions we then see that the intensity integral will span the representations in the direct product of A2 x F, x F2, and this reduces as follows ... 

Table 6.20. Character table for the point group and the characters of the reducible representation in a tetrahedral ML4 complex...

The familiar splitting of the d level in square-planar, tetrahedral or octahedral molecules and complex ions are less conveniently discussed in terms of a quadrupolar field, because their symmetry is higher than T>2h- The symmetry point groups involved D4/1, Tj and O/i, are non-commutative by which is meant that the product of two symmetry operations may depend on the order in which they are carried out. The relevant properties of non-commutative symmetry point groups are illustrated below with the smallest of the three, D4/1. It contains just twice the number of sym-ops as its subgroup The relation... 

Both of the out-of-plane modes are non-degenerate. The kernel of the a2u mode is C4V, the point group of a tetragonal pyramid, such as would be generated by the approach of a fifth ligand atom along z. Continued displacement along the 62 coordinate takes square-planar NiFj" into D2d, and eventually converts it into a tetrahedral complex this interconversion will be discussed in detail in a Chapter 11. 

Fig. 3.9c) and [Fe(CN)6]. There is no centre of symmetry in a tetrahedron but there is one in an octahedron, and this distinction has consequences with regard to the observed electronic spectra of tetrahedral and octahedral metal complexes (see Section 20.7). Members of the icosahedral point group are uncommon, e.g. [B]2Hj2] (Fig. 3.9d). 

A 1 2 complex between Ni " " and N,N-dimethyl-/3-mercaptoethylamine, Me2NCH2CH2SH, has been synthesized. It is desired to establish the configuration (cis or trans) of the complex and the coordination (square planar or tetrahedral) of Ni +. Explain how the following information enables one to elucidate the stereochemistry. Also state the point group to which it belongs and sketch the bis(N,JV-dimethyl- 3-mercaptoethylamine)nickel(ll) molecule. 

Tetrahedral complexes and molecules, shown in Figure 1, with two or three identical ligands M hc and M jb) have only one element of symmetry in addition to E. This element is a plane between the identical H-gands. Such entities are classified into a point group. The group is... 

Figure 15b represents a dinuclear complex formed by a pair of tetrahedral complexes Af bc and a metallic bond. Such a molecule has only an identity element of symmetry. However, as all the identical ligands are placed exactly opposite to each other, an indistinguishable appearance can be obtained by interchanging the opposite positions, which means that it possesses the centre of inversion i. Hence, this complex is an example of the point group Q. The meso form of the organic compound, CHCIBr—CHCIBr, is another example of the point group Q. 

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