key term - [Cr(H2O)6]3+

Definition

[Cr(H2O)6]3+ is a coordination complex where chromium is at the center, surrounded by six water molecules as ligands, resulting in a +3 charge on the complex. This species is an important example of an octahedral complex, illustrating key concepts related to coordination chemistry, such as ligand substitution reactions and the geometric arrangements that influence chemical behavior.

5 Must Know Facts For Your Next Test

1. [Cr(H2O)6]3+ is commonly encountered in solution and is known for its characteristic color, which results from d-d electron transitions within the chromium ion.
2. The +3 oxidation state of chromium in [Cr(H2O)6]3+ makes it more stable and less reactive compared to its +6 counterpart in other complexes.
3. This complex can undergo substitution reactions where water molecules can be replaced by other ligands, such as chloride ions or ammonia, leading to different properties and colors.
4. The stability and reactivity of [Cr(H2O)6]3+ can be influenced by factors such as the nature of the incoming ligand and the steric and electronic effects related to the ligands present.
5. [Cr(H2O)6]3+ exhibits both kinetic and thermodynamic aspects during substitution reactions, with some ligands being more labile (faster substitution) than others.

Review Questions

• How does the structure of [Cr(H2O)6]3+ influence its reactivity during ligand substitution reactions?
  • [Cr(H2O)6]3+ has an octahedral geometry with six water molecules coordinated to chromium, which creates a specific spatial arrangement. This geometry impacts how easily ligands can approach and replace the existing water ligands during substitution reactions. Factors like sterics and the charge of incoming ligands also play crucial roles in determining how readily these substitutions occur.
• Discuss the significance of charge and oxidation state in determining the properties of [Cr(H2O)6]3+ as compared to [Cr(H2O)6]2+.
  • The +3 oxidation state in [Cr(H2O)6]3+ leads to a more stable configuration than in [Cr(H2O)6]2+, which is +2. This difference affects properties such as color, reactivity, and stability towards oxidation or reduction. In terms of ligand substitution, [Cr(H2O)6]3+ generally shows lower reactivity than its +2 counterpart because it has a greater tendency to retain its ligands due to its increased positive charge.
• Evaluate the factors that affect the kinetics of substitution reactions in complexes like [Cr(H2O)6]3+, considering both thermodynamic stability and kinetic lability.
  • In complexes such as [Cr(H2O)6]3+, factors influencing kinetics include ligand characteristics (size, charge, electron-donating ability), the nature of the metal center, and solvent interactions. Thermodynamic stability relates to the overall energy favorability of the complex; however, kinetic lability determines how fast substitutions occur. For example, small, highly charged ligands may rapidly displace water due to their strong interactions with chromium, while bulkier or less charged ligands may lead to slower substitutions despite possibly being thermodynamically favorable.

Related terms

Ligand:

A ligand is a molecule or ion that can donate a pair of electrons to a central metal atom or ion in a coordination complex.

Octahedral Geometry:

Octahedral geometry refers to the arrangement of six ligands around a central metal atom in a way that they occupy the corners of an octahedron.

Substitution Reaction: A substitution reaction involves replacing one ligand in a coordination complex with another ligand, affecting the properties of the complex.