Question

For coordination compounds \(\mathrm{Na}_{3}\left[\mathrm{Ir} \mathrm{Cl}_{6}\right]\) and \(\left[\mathrm{Mo}(\mathrm{CO})_{4}\right] \mathrm{Br}_{2},\) identify in cach case (a) the ligands. (b) the central metal ion and its charge. (c) the formula and charge of the complex ion. (d) any ions not part of the complex ion.

Short answer

Na3[IrCl6]: ligands are Cl, Ir+3, [IrCl6]3-, Na+ [Mo(CO)4]Br2: ligands are CO, Mo, [Mo(CO)4] (neutral), Br-

Step-by-step solution

Identify ligands in the compounds

For the compound \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the ligands are the chlorine atoms \( \text{Cl}^- \). In the compound \( [\text{Mo} (\text{CO})_4 ]\text{Br}_2 \), the ligands are the carbonyl groups \( \text{CO} \).

Identify the central metal ion and its charge

In \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the central metal ion is iridium \( \text{Ir} \). The complex ion \( [\text{Ir}\text{Cl}_6]^{3-} \) indicates that iridium has a charge of \( +3 \). In \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), the central metal ion is molybdenum \( \text{Mo} \). It is in a neutral complex as no net charge is given.

Determine the formula and charge of the complex ion

For \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the complex ion is \( [\text{Ir}\text{Cl}_6]^{3-} \), since it requires three positive sodium ions to neutralize this charge.For \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), the complex ion is \( [\text{Mo}(\text{CO})_4] \) with a neutral charge, as no charge is indicated and the compound is completed by two bromide ions.

Identify ions not part of the complex ion

In the compound \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the ions not part of the complex ion are the sodium ions \( \text{Na}^+ \). In the compound \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), the ions not part of the complex are the bromide ions \( \text{Br}^- \).

Key concepts

Ligands

In coordination compounds, ligands play a fundamental role as they are what bind to the central metal ion. They are molecules or ions that donate a pair of electrons to form a coordination bond with the metal. This action helps stabilize the metal ion in a complex. Ligands can be neutral molecules like water or carbon monoxide, or they can be anions like chloride.

In the compound \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the ligands are six chloride ions \( \text{Cl}^- \). These provide the electrons needed to form bonds with the central metal. On the other hand, in \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), the ligands are four carbon monoxide molecules \( \text{CO} \), each acting as a strong electron donor.

Central Metal Ion

The central metal ion is at the heart of the coordination compound. It is the species to which ligands are attached. The metal ion's oxidation state can greatly influence the stability and reactivity of the entire complex.

In \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the central metal ion is iridium \( \text{Ir} \). The charge on the complex suggests that iridium has an oxidation state of \(+3\). Conversely, in the compound \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), molybdenum \( \text{Mo} \) is the central metal ion. There is no net charge on this complex, indicating that molybdenum remains in its neutral state.

Complex Ion

A complex ion is formed when a central metal ion is bonded to one or more ligands through coordinate bonds. This can either be anionic, cationic, or neutral, depending on the charges of the metal and the ligands.

For \( \text{Na}_3[\text{Ir}\text{Cl}_6] \), the complex ion is \( [\text{Ir}\text{Cl}_6]^{3-} \). This indicates that the entire complex carries a 3- charge, which is why three sodium ions are needed to balance it. Meanwhile, \( [\text{Mo}(\text{CO})_4] \) constitutes a neutral complex ion as presented in \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \). This means there is no overall charge on the complex.

Coordination Chemistry

Coordination chemistry is the study of compounds characterized by coordinate bonds between metal ions and ligands. These compounds have fascinating structural features and diverse chemical properties that make them very important in both chemistry and industry.

Such compounds can range from simple structures to very intricate ones. Their properties are highly influenced by the type of ligands and the oxidation state of the metal. Understanding coordination chemistry allows chemists to predict and explain the reactivity and stability of these compounds, which is crucial for applications like catalysis or material design.

• Complexes such as \( \text{Na}_3[\text{Ir}\text{Cl}_6] \) highlight how metal ions interact with anions to form stable entities.
• Neutrally charged complexes, like \( [\text{Mo}(\text{CO})_4]\text{Br}_2 \), show how even without net charge, significant coordination can occur to create stable structures.