Question

The number of viable coordination isomers possible for the complex \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\) should be ?

Short answer

Two coordination isomers are possible: \([\mathrm{Pt(NH}_3)_4][\mathrm{CuCl}_4]\) and \([\mathrm{PtCl}_4][\mathrm{Cu(NH}_3)_4]\).

Step-by-step solution

Understanding Coordination Isomers

Coordination isomers differ in the arrangement of ligands between the coordination sphere of the cation and the anion. In \([\mathrm{Pt(\mathrm{NH}_3)_4}][\mathrm{CuCl}_4]\), the amine ligands (\(\mathrm{NH}_3\)) are coordinated to Pt and the chloride ions (\(\mathrm{Cl}^-\)) to Cu. Isomers result by swapping these ligands.

Possible Ligand Swaps

Review the complex: it consists of a Pt-containing complex \([\mathrm{Pt(\mathrm{NH}_3)_4}]\) and a Cu-containing complex \([\mathrm{CuCl}_4]\). Consider swaps that maintain charge balance and viable coordination structures, such as moving Cl and NH₃ ligands between Pt and Cu.

Determining Reasonable Swaps

Since Pt usually coordinates with \([\mathrm{NH}_3]\) in tetrahedral or square planar and Cu generally coordinates with \([\mathrm{Cl}]^-\), potential swaps involve creating alternative complexes like \([\mathrm{PtCl}_4][\mathrm{Cu(NH}_3)_4]\) and checking for compounds like \([\mathrm{PtCl}_2(NH}_3)_2][\mathrm{Cu(NH}_3)_2\mathrm{Cl}_2]\).

Count Viable Isomers

Review possible ligand swaps: (1) \([\mathrm{Pt(NH}_3)_4][\mathrm{CuCl}_4]\), (2) \([\mathrm{PtCl}_4][\mathrm{Cu(NH}_3)_4]\). Others such as \([\mathrm{PtCl}_2(NH}_3)_2][\mathrm{Cu(NH}_3)_2\mathrm{Cl}_2]\) may not stabilize due to mismatches in typical coordination preferences.

Key concepts

Ligand Swapping

Ligand swapping is a fascinating process where the ligands attached to different metal centers in a complex can exchange places. This idea helps explain the formation of coordination isomers. Imagine our complex, \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\), which has ligands amine \((\mathrm{NH}_3)\) bound to platinum \(\mathrm{Pt}\) and chloride \((\mathrm{Cl}^-)\) bound to copper \(\mathrm{Cu}\). Through ligand swapping, we can test out different configurations of these ligands around the metal centers.The basic principle of swapping is to maintain the identity of the compounds, where ligands switch from one metal to another, such as having chloride take the place of amine in the coordination sphere of \(\mathrm{Pt}\), and vice versa for \(\mathrm{Cu}.\) This is really important because it leads us to new and stable isomers of a complex, potentially affecting their chemical properties and reactivity.

Coordination Sphere

The coordination sphere is like the inner circle of a coordination complex. It consists of the central metal atom and all the ligands directly bonded to it. In our complex \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\), \(\mathrm{Pt}\) and its four ammonia ligands form one coordination sphere, and \(\mathrm{Cu}\) with four chloride ions form another. It's important to note that the coordination sphere is crucial for determining the chemical properties and behavior of the complex. Ligands inside this sphere are involved in the primary coordination bonds with the metal. When these are rearranged, as in coordination isomerism, the compound's properties can change.To visualize better, think of the coordination sphere as the innermost "bubble" holding the heart of the metal-ligand interactions intact, while the external environment could affect but doesn't break these primary bonds.

Charge Balance

Maintaining charge balance in coordination isomers is essential for the stability of the compound. Charge balance ensures that, despite the swapping of ligands, the overall charge of the complex remains unchanged.In \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\), the original complex is neutral. When we think about ligand swapping to create potential isomers like \([\mathrm{PtCl}_4][\mathrm{Cu(NH}_3)_4]\), each new arrangement must still result in electrically neutral or adequately charged complexes.Keeping the charge balanced involves checking the oxidation states and the number of positive and negative charges within each new coordination structure. This requirement constrains which ligand arrangements are possible or viable during swapping, ensuring realistic isomeric forms.

Viable Coordination Structures

Viable coordination structures refer to isomers that are synthetically feasible and stable in their physical form. When rearranging ligands between metal centers, only certain configurations will lead to stable coordination structures that do not violate chemical principles or typical metal coordination patterns.In determining the viability of \(\left[\mathrm{PtCl}_{4}\right]\left[\mathrm{Cu(NH}_3)_{4}\right]\), would \(\mathrm{Pt}\) and \(\mathrm{Cu}\) comfortably host swapped ligands while maintaining their preferred coordination geometries, such as square planar or tetrahedral shapes?These considerations guide us when examining potential isomers like \([\mathrm{Pt(NH}_3)_4][\mathrm{CuCl}_4]\), alongside other speculative structures. If a proposed isomer would disrupt the balance too greatly, or violate stable coordination types, it wouldn't be considered viable on paper or in practice.