Question

How many geometric isomers are possible for the square-planar complex ion \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)(\mathrm{CN}) \mathrm{Cl}_{2}\right]^{-} ?\)

Short answer

There are 2 geometric isomers possible.

Step-by-step solution

Identify the Structure

The ion is square-planar, which means it has a planar, roughly square arrangement of its ligands around a central metal atom, in this case, platinum (Pt). The ligands are two chlorine atoms (Cl), one cyanide ion (CN), and one ammonia molecule (NH extsubscript{3}).

Determine Possible Arrangements

We arrange the four ligands around the Pt center. Given the symmetry and position differences for square-planar complexes, different configurations can arise based on which ligands are adjacent or opposite.

Analyze Ligand Positions for Isomers

For each ligand, examine physical adjacency or diagonal placement relative to the others to form distinct geometric arrangements. Possible positions include: adjacent pairs of NH extsubscript{3}, CN, and Cl, or opposite pairs.

Count Unique Isomers

By arranging the ligands, it is possible to have different arrangements: 1) NH extsubscript{3} and CN adjacent, with Cl extsubscript{2} opposite, and 2) NH extsubscript{3} and CN opposite each other, with each paired next to two Cl's. There are no more unique arrangements making a total of 2 geometric isomers.

Key concepts

Square-Planar Complexes

Square-planar complexes are fascinating structures found in coordination chemistry. They feature a metal ion at the center with ligands positioned at the corners of a square plane. This geometric arrangement means the metal is coordinated by four atoms or groups.

The most commonly associated metal with square-planar complexes is platinum, but other transition metals can also form them. The symmetry of this complex gives rise to interesting chemical properties and potential geometric isomers.

In the square-planar arrangement, the 90-degree angles between adjacent ligands offer distinct possibilities in terms of spatial arrangement, especially when different types of ligands are involved. This can lead to differences in physical and chemical properties among the isomers.

Ligand Arrangement

In square-planar complexes, the arrangement of ligands around the central metal is crucial for understanding geometry and isomerism. Ligands like Cl, NH extsubscript{3}, and CN can occupy any of the four positions around the metal.

Consider each pair of ligands, since they can be either adjacent or opposite each other. This difference can lead to distinct geometric structures known as geometric isomers. The spatial relationship between ligands affects the properties and reactivity of the complex.

When arranging ligands, understanding which are adjacent or opposite helps determine the possible isomers. The choice of positions will affect, for example, how the ligands interact or how the complex absorbs light.

Platinum Complex

The platinum complex \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)(\mathrm{CN})\mathrm{Cl}_{2}\right]^{-}\) exemplifies a classic square-planar design. Here, platinum serves as the central metal atom, coordinating with four distinct ligands.

Platinum is favored in square-planar structures due to its electronic configuration. This configuration stabilizes the planar form and facilitates interesting chemical behavior. This particular complex consists of two chlorine ions, one ammonia, and one cyanide ligand.

Platinum complexes are well-known for their role in catalysis and medicinal chemistry. Understanding the coordination and ligand positions within them is essential for predicting and explaining their reactivity and functionality.

Coordination Chemistry

Coordination chemistry explores how metal ions interact with molecules or ions, known as ligands. It studies the formation of complex structures where ligands coordinate to a central metal.

This field delves into geometries such as square-planar and others (e.g., octahedral). The specific geometry depends on various factors:

• The metal ion's electronic configuration
• The number of ligands
• The types of bonds formed

Coordination chemistry is foundational in understanding how complexes like the platinum example form. It enables the prediction of properties and the utility of these complexes in practical applications. It provides insight into behavior, reaction pathways, and stability, crucial in diverse areas like catalysis and drug design.