Which of the following complexes can exist as enantiomers? Draw their structures.
(a) [Cr(en)₃]³⁺
(b) cis-[Co(NH₃)Cl]²⁺
(c) trans-[Co(en)₂(NH₃)Cl]²⁺
(d) [Pt(NH₃)₃Cl₃]⁺

Verified step by step guidance

1. Identify the type of isomerism: Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They typically occur in octahedral complexes with bidentate ligands.
2. Analyze each complex: (a) [Cr(en)_3]^{3+} is an octahedral complex with three bidentate ethylenediamine (en) ligands, which can form chiral centers, making it possible to have enantiomers.
3. Consider the geometry: (b) cis-[Co(NH_3)Cl]^{2+} is a square planar complex, which typically does not exhibit chirality, so it cannot have enantiomers.
4. Evaluate the ligand arrangement: (c) trans-[Co(en)_2(NH_3)Cl]^{2+} has a trans configuration, which usually does not allow for chirality, thus it cannot exist as enantiomers.
5. Check the coordination and symmetry: (d) [Pt(NH_3)_3Cl_3]^{+} is a square planar complex, which generally does not form enantiomers due to its symmetry.

Key Concepts

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image, much like left and right hands. Molecules that possess chirality typically have a carbon atom bonded to four different substituents, leading to two distinct configurations known as enantiomers. Understanding chirality is essential for determining whether a complex can exist as enantiomers.

Coordination Complexes

Coordination complexes consist of a central metal atom bonded to surrounding ligands, which can be neutral molecules or ions. The arrangement of these ligands around the metal can lead to different geometric isomers, such as cis and trans forms. The specific geometry of these complexes plays a crucial role in their potential to exhibit chirality and form enantiomers.

Geometric Isomerism

Geometric isomerism occurs when ligands in a coordination complex can be arranged in different spatial orientations, leading to distinct isomers. In octahedral complexes, for example, ligands can be positioned adjacent to each other (cis) or opposite each other (trans). This concept is vital for analyzing the given complexes, as it helps determine which can exist as enantiomers based on their geometric configurations.