Question

Write the formulas and names for the coordination isomers of \(\left[\mathrm{Co}(\mathrm{en})_{3}\right]\left[\mathrm{Cr}(\mathrm{ox})_{3}\right] .\)

Short answer

The coordination isomer of \(\left[\mathrm{Co}(\text{en})_{3}\right]\left[\mathrm{Cr}(\text{ox})_{3}\right]\) is \(\left[\mathrm{Co}(\text{ox})_{3}\right]\left[\mathrm{Cr}(\text{en})_{3}\right]\).

Step-by-step solution

Understanding Coordination Isomers

Coordination isomers arise when the composition of ligands in the coordination sphere of metal cations can be interchanged without changing the overall stoichiometry of the complex compounds. In the given complex, \(\mathrm{Co}(\text{en})_{3}\) and \(\mathrm{Cr}(\text{ox})_{3}\) can exchange their ligands, where 'en' stands for ethylenediamine and 'ox' stands for oxalate ion.

Identify Possible Ligand Exchange

The original complex, \(\left[\mathrm{Co}(\text{en})_{3}\right]\left[\mathrm{Cr}(\text{ox})_{3}\right]\), suggests possible isomerism through the exchange of ligands between cobalt and chromium centers. The cobalt complex has 3 bidentate ethylenediamine ligands and the chromium complex has 3 bidentate oxalate ions.

Write the Formulas for Coordination Isomers

For coordination isomers of the given complex, there would be an exchange of ligands between the two metal cations, yielding the following isomers: \(\textbf{Isomer 1}: \left[\mathrm{Co}(\text{ox})_{3}\right]\left[\mathrm{Cr}(\text{en})_{3}\right]\) and \(\textbf{Isomer 2}: \left[\mathrm{Co}(\text{en})_{3}\right]\left[\mathrm{Cr}(\text{ox})_{3}\right]\). Note that Isomer 2 is the original compound, and Isomer 1 is the coordination isomer where the ligands have been swapped.

Key concepts

Coordination Compounds

Coordination compounds, also known as coordination complexes, are unique molecules consisting of a central metal atom or ion bonded to a surrounding array of molecules or ions, which are called ligands. These ligands are typically Lewis bases that can donate a pair of electrons to form coordinate covalent bonds with the metal center.

The characteristics of a coordination compound include its shape, color, magnetism, and reactivity, which are influenced by the nature of the metal ion, the types of ligands attached, and the coordination number, which is the number of points at which ligands are attached to the metal. For example, the compound \[\mathrm{Co}(\mathrm{en})_{3}\] features cobalt as the central metal ion with three bidentate ethylenediamine ligands.

Ligand Exchange

Ligand exchange is a fundamental process in coordination chemistry where one ligand in a coordination complex is replaced by another ligand. This can occur spontaneously or may be induced by various factors such as a change in temperature or the presence of another potential ligand in the solution.

Understanding ligand exchange is crucial for applications in catalysis and drug delivery, as it governs the stability and reactivity of coordination compounds. For instance, \[\mathrm{Co}(\mathrm{en})_{3}\] can undergo ligand exchange with \[\mathrm{Cr}(\mathrm{ox})_{3}\], resulting in the creation of coordination isomers where their ligands are interchanged.

Complex Ion Nomenclature

Nomenclature of complex ions involves a set of rules for naming coordination compounds systematically. When naming a coordination complex, you start with the ligands followed by the metal, and if the complex is an anion, the metal’s name ends in ‘-ate’. The prefixes 'mono', 'di', 'tri', etc., are used before the names of the ligands to indicate their quantities.

The names of the ligands are also modified; anionic ligands end in ‘-o’, while neutral ligands are typically called by their organic name. Using the example given, the name for \[\left[\mathrm{Co}(\mathrm{en})_{3}\right]\left[\mathrm{Cr}(\mathrm{ox})_{3}\right]\] follows these rules, and for its coordination isomer \[\left[\mathrm{Co}(\mathrm{ox})_{3}\right]\left[\mathrm{Cr}(\mathrm{en})_{3}\right]\], the names of metal centers would change accordingly.

Coordination Chemistry

Coordination chemistry is the study of compounds that feature coordinate covalent bonds between a central metal atom and surrounding ligands. It bridges aspects of inorganic and biochemistry with insights into metal ion behavior, electronic structures, and the properties of complexes.

Coordination complexes play pivotal roles in various biological processes and industrial applications. For example, the field of coordination chemistry explains the functioning of metalloenzymes in biological systems, aspects of color in gemstones, and the production of materials with specific magnetic or electronic properties. In our textbook exercise, the swapping of ligands to form coordination isomers is a direct application of principles of coordination chemistry.