Question

Write names for the following coordination compounds: (a) \(\left[\mathrm{Cd}(\mathrm{en}) \mathrm{Cl}_{2}\right]\) (b) \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\) (c) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{CO}_{3}\right] \mathrm{Cl}\) (d) \(\left[\mathrm{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\)

Short answer

The names of the given coordination compounds are: (a) dichloridoethylenediaminecadmium(II) (b) potassium hexacyanidomanganese(II) (c) pentaamminecarbonatochromium(III) chloride (d) tetraamminediaquairidium(III) tri-nitrate

Step-by-step solution

(a) Identify the central atom and ligands for the first coordination compound

For the compound \(\left[\mathrm{Cd}(\mathrm{en}) \mathrm{Cl}_{2}\right]\), the central metal atom is cadmium (Cd) and the ligands are ethylenediamine (en) and two chloride ions (Cl).

(a) Name the first coordination compound

According to IUPAC nomenclature rules, the name of this compound is "dichloridoethylenediaminecadmium(II)".

(b) Identify the central atom and ligands for the second coordination compound

For the compound \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\), the central metal atom is manganese (Mn) and the ligands are six cyanide ions (CN). Additionally, there are four potassium ions (K) outside the coordination sphere.

(b) Name the second coordination compound

According to IUPAC nomenclature rules, the name of this compound is "potassium hexacyanidomanganese(II)".

(c) Identify the central atom and ligands for the third coordination compound

For the compound \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{CO}_{3}\right]\mathrm{Cl}\), the central metal atom is chromium (Cr) and the ligands are five ammonia molecules (NH3) and one carbonate ion (CO3). Additionally, there is one chloride ion (Cl) outside the coordination sphere.

(c) Name the third coordination compound

According to IUPAC nomenclature rules, the name of this compound is "pentaamminecarbonatochromium(III) chloride".

(d) Identify the central atom and ligands for the fourth coordination compound

For the compound \(\left[\mathrm{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\), the central metal atom is iridium (Ir) and the ligands are four ammonia molecules (NH3) and two water molecules (H2O). Additionally, there are three nitrate ions (NO3) outside the coordination sphere.

(d) Name the fourth coordination compound

According to IUPAC nomenclature rules, the name of this compound is "tetraamminediaquairidium(III) tri-nitrate".

Key concepts

IUPAC Nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) has established a systematic method of naming chemical compounds, which ensures that each compound has a unique and universally accepted name. In coordination chemistry, the IUPAC nomenclature system is vital for clearly specifying the composition of coordination compounds.

When naming a coordination compound, we identify and name the ligands first, followed by the central metal atom. Ligands are named in alphabetical order regardless of their charge, with prefixes like 'di-', 'tri-', 'tetra-', etc., to indicate the number of each type. Neutral ligands are typically given their common names (e.g., water is 'aqua'), whereas anionic ligands end in 'o' (e.g., chloride becomes 'chlorido').

The central metal's name is then stated, with a Roman numeral in parentheses indicating the metal's oxidation state. If there's a counter-ion present (outside the coordination sphere), it is named last, just like in the naming of salts. For example, the name 'dichloridoethylenediaminecadmium(II)' reveals that the compound includes a cadmium ion with an oxidation state of +2, coordinated with two chloride ions and one ethylenediamine molecule.

Transition Metal Complexes

In the realm of coordination chemistry, transition metal complexes form the centerpiece, with their unique ability to bond with various ligands creating an array of structures and colors. These complexes consist of a transition metal ion surrounded by molecules or anions termed ligands.

The coordination of ligands to a central metal ion is facilitated through coordinate covalent bonds, which are formed when both electrons in a bonding pair come from the same atom. Transition metals are particularly suited to forming such bonds owing to their d orbitals, which can accommodate the shared electron pairs.

Several examples highlighted in the exercise, such as \(\mathrm{K}_{4}[\mathrm{Mn}(\mathrm{CN})_{6}]\) or \(\left[\mathrm{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\), illustrate diverse coordination numbers and ligand types. These factors, among others, ultimately influence the properties such as geometry, stereochemistry, and reactivity, of the transition metal complexes.

Ligands in Coordination Chemistry

Ligands are ions or molecules that bind to a central metal atom to form a coordination complex. They are pivotal in dictating the structure and function of coordination compounds.

In the examples given in the exercise, we encounter a variety of ligands, such as ethylenediamine (en), chloride (Cl), cyanide (CN), ammonia (NH3), carbonate (CO3), and water (H2O). Ligands can be classified based on the number of attachment points or bonding locations they provide to the metal center:

• Monodentate ligands: Bind through a single atom, like chloride or water.
• Bidentate ligands: Have two binding sites, such as ethylenediamine, which can wrap around the metal ion and bind it at two points.
• Polydentate (or chelating) ligands: Possess multiple binding sites, allowing them to form stable rings with the central atom, greatly enhancing the stability of the complex.

These ligands can also bring about different colors in coordination compounds due to variations in metal-ligand bonding, which affects the d-electron configuration of the metal ion. As a result, understanding ligands is crucial for predicting and explaining the behavior of transition metal complexes in chemical reactions.