Ionization Isomerization

Although the compounds [Pt(en)2Cl2]Br2 and [Pt(en)2Br2]Cl2 have the same empirical formulas, they are quite different compounds. For example, the first gives Br- when dissolved in water, whereas the second gives Cl-. This occurs because in the first case, the Cl- ions are coordinated to the Pt4+, whereas in the second case the Br- ions are coordinated to the metal ion. The isomerism in cases such as these is known as ionization isomerism. It is easy to see that many pairs of compounds could be considered as ionization isomers, among them the following examples ... 

Hydrate isomerism is quite analogous to ionization isomerism. The compound Cr(H20)5Ci2+ (C1 )2 H20 contains one Cr—Cl bond and five Cr—O bonds per complex whereas its isomer, Cr(H20)4Clt C1 2H20, has two Cr—Cl bonds and only four Cr—O bonds per complex. The first of these yields three ions per gram-atom of chromium when dissolved in water (as may be checked by freezing-point measurements), whereas the second yields but two ions per complex. Those water molecules not directly coordinated to chromium are probably present as lattice water. ... 

This form of isomerism, sometimes known as hydrate isomerism in the special case where water is involved, is similar in some ways to ionization isomerism. Solvate isomers differ by whether or not a solvent molecule is directly bonded to the metal ion or merely present as free solvent in the crystal lattice or solution. An example is provided by the aqua complex [Cr(H20)JCl3 and its solvate isomer [Cr(H20)5Cl]Cl2.H20. 

Ionic radius 22, 23, 35 Ionization energy 23 Ionization enthalpy 23 Ionization isomerism 65... 

Ionization Isomerism The ionization isomers [CoiNHjljBriSO and [Co NH3)]S04]6r dissolve in water to yield different ions and thus react differently to various reagents ... 

Compounds with the same formula, but which give different ions in solution, exhibit ionization isomerization. The difference is in which ion is included as a ligand and... 

Ionization isomerism is another case defined by recognizing that an empirical formula allows some options for the coordination sphere of the metal. It is essentially the same situation as hydrate isomerism, but involves ligands other than water. For example, consider the inert cobalt(III) compound CoBr(S04>5(NH3), which forms two different compounds, one violet, the other red. We know these now as [CoBr(NH3)5](S04) and [Co(NH3)5(S04)]Br, which differ in the choice of which anion occupies the coordination sphere, the other remaining as the counter-ion (Figure 4.25). 

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