Which type of isomer can form due to the exchange of a ligand with a counter-ion dissolved in solution?

Ionization isomers arise when a ligand in a complex can be replaced or exchanged with an anion (counter-ion) present in the solution. This type of isomerization significantly changes the overall composition of the complex by altering its ionic components while keeping the coordination number of the metal center the same.

For example, consider a coordination complex like [Cu(NH3)4]SO4. When the ammonia ligand is replaced by the sulfate ion from the solution, a different isomer like Cu(NH3)3(SO4) can form, where the composition of the counter-ions is different. The presence of different counter-ions leads to different behaviors in solution, changes in solubility, and often different chemical properties.

Other types of isomers, such as hydrate, linkage, and coordination isomers, involve different structural or connectivity changes. Hydrate isomers involve the presence of water molecules in different positions, linkage isomers arise from ligands being able to bind through different atoms, and coordination isomers involve changes in the arrangement of ligands within different complexes. However, these processes do not involve the exchange with counter-ions as seen in ionization isomerism.