Isomerism in coordination compounds

FIGURE 16.18 The various types of isomerism in coordination compounds. 

The present discussion of isomerism in coordination compounds is not, nor was it intended to be, comprehensive and exhaustive. The examples considered are an eclectic selection, and many important systems may have been neglected through ignorance. An obvious omission is any detailed consideration of polynuclear complexes139,256"259 and it is, of course, a quite arbitrary decision not to include any consideration of organometallic species. Other neglected issues, such as the development of a truly comprehensive system of stereochemical nomenclature, are perhaps not yet capable of solution. Nevertheless, it is to be hoped that the principal factors to be considered... 

Although other types of isomerism in coordination compounds exist, the types described in this section represent the most important types. 

In a review, discussing a wide range of previous studies of isomerization in coordination compounds of cobalt or chromium with several representative diamines, Yamaguchi et al. [59] concluded that, even in the solid state, any ligand in these metal coordination compounds was unexpectedly easy to move. Most of these isomerizations, including 22 reactions trans to cis and cis to trans steps), occurred between about 400 and 520 K. 

Isomers can be broadly divided into two major classes constitutional isomers and stereoisomers. In Chapter 25 we discussed isomerism in coordination compounds, and in Chapter 27 we learned about some isomeric organic compounds. In this chapter we will take a more systematic look at some three-dimensional aspects of organic structures—a subject known as stereochemistry ( spatial chemistry ). 

This sequence is an ECC (or EC2C) reaction. The products of one-electron transfers can also rearrange (see Figure 12.1.1, path 3), because a bond is weakened. For similar reasons, electron transfers can also lead to loss of ligands, substitution, or isomerization in coordination compounds. Examples include... 

In this chapter, the fundamental features of the infrared spectra of inorganic compounds were introduced. Effects, such as the degree of hydration, on the appearance of infrared spectra were described. The infrared spectra of inorganic molecules are determined by the normal modes of vibration exhibited by such molecules and these were sunnnarized and common examples provided. Infrared spectroscopy is widely used to characterize coordination compounds and the important effects of coordination were introduced. Isomerism in coordination compounds may also be characterized by using infrared techniques and examples were provided. Infrared spectroscopy is extensively used to characterize metal carbonyl compounds and examples of how the bonding in such compounds may be understood were provided. The main infrared bands associated with organometaUic compounds were also introduced. Finally, examples of how infrared spectroscopy may be employed to understand the structures of mineral compounds were included. 

Isomerism in Coordination Compounds 25-6 Structurai (Constitutionai) isomers 25-7 Stereoisomers Bonding in Coordination Compounds 25-8 Crystal Field Theory 25-9 Color and the Spectrochemical Series... 

Isomerism Isomers are compounds with the same molecular formula (or the same simplest formula, in the case of ionic compounds) but with different arrangements of atoms. Because their atoms are differently arranged, isomers have different properties. There are many possibiUties for isomerism in coordination compounds. The smdy of isomerism can lead to information about atomic arrangement in coordination compounds. Wauer s research on the isomerism of coordination compounds finally convinced others that his views woe essentially correct. 

---