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) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{CO}_{3}\right)\right] \mathrm{Cl}\) (d) \(\left[\operatorname{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\)

Short answer

The names of the given coordination compounds are: (a) dichloroethylenediaminecadmium(II) (b) potassium hexacyanomanganate(IV) (c) pentaamminecarbonatochromium(III) chloride (d) hexaamminediaquairidium(III) nitrate

Step-by-step solution

Identify the central atoms and ligands in each compound

For each compound, the central atom is the metal atom that is bonded to the ligands. Ligands are ions or molecules surrounding the central atom and bonded to it. (a) In \(\left[\mathrm{Cd}(\mathrm{en})\mathrm{Cl}_{2}\right]\), Cd is the central atom and en and Cl are the ligands. (b) In \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\), Mn is the central atom and CN is the ligand. (c) In \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{CO}_{3}\right)\right]\mathrm{Cl}\), Cr is the central atom and NH3 and CO3 are the ligands. (d) In \(\left[\operatorname{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\), Ir is the central atom, NH3 and H2O are the ligands, and NO3 is the counterion.

Name the central atom and ligands

We will now write the names for the central atoms and the ligands, taking into account their oxidation states and the multiplicity of the ligands. (a) Cd is Cadmium. The en ligand is ethylenediamine, and the Cl ligand is chloride. (b) Mn is Manganese. The CN ligand is cyanide. (c) Cr is Chromium. The NH3 ligand is ammine and the CO3 is carbonate. (d) Ir is Iridium. The NH3 ligand is ammine, the H2O ligand is aqua, and the NO3 counterion is nitrate.

Write the coordination compound names

Following the IUPAC rules and our findings in the previous steps, we can now write the names for each coordination compound. (a) \(\left[\mathrm{Cd}(\mathrm{en})\mathrm{Cl}_{2}\right]\) - This compound is called dichloroethylenediaminecadmium(II). (b) \(\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]\) - This compound is called potassium hexacyanomanganate(IV). (c) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{CO}_{3}\right)\right]\mathrm{Cl}\) - This compound is called pentaamminecarbonatochromium(III) chloride. (d) \(\left[\operatorname{Ir}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2}\mathrm{O}\right)_{2}\right]\left(\mathrm{NO}_{3}\right)_{3}\) - This compound is called hexaamminediaquairidium(III) nitrate.

Key concepts

Understanding Inorganic Chemistry

Inorganic chemistry is a branch of chemistry that deals with inorganic compounds, typically those which do not contain carbon-hydrogen bonds. These include metals, salts, and minerals, among many others. Understanding inorganic chemistry involves studying the synthesis and behavior of inorganic and organometallic compounds. This field covers all chemical compounds except the myriad organic compounds (carbon-based compounds, usually containing C-H bonds) which are the subjects of organic chemistry.

In the context of coordination compounds, such as the ones presented in the exercise, inorganic chemistry explores the structures, properties, and reactions of molecules that contain a central metal atom or ion surrounded by different ligands. These coordination compounds are pivotal in numerous areas, including catalysis, materials science, and biochemistry. As students of inorganic chemistry, learning about these compounds includes understanding their compositions, geometries, and the nature of the bond between the metal and the ligands.

The Role of Ligands in Coordination Chemistry

Ligands in coordination chemistry are ions or molecules that bind to the central metal atom or ion in a coordination compound. They are essential for creating the complex structures that give these compounds their unique properties. A ligand can be an anion, a neutral molecule, or a cation, and they attach to the central metal atom by donating a pair of electrons to form a coordinate covalent bond.

Ligands can be classified based on the number of electron pairs they donate. Monodentate ligands, like water (aqua) and ammonia (ammine), donate one pair of electrons. Bidentate ligands, such as ethylenediamine (en), donate two pairs of electrons, one from each of two donor atoms. The flexibility and type of ligands determine the structure and reactivity of the coordination compound. The exercise that students encounter requires understanding these ligand-metal interactions which directly influence the nomenclature and chemical properties of coordination compounds.

Grasping IUPAC Naming Conventions

The International Union of Pure and Applied Chemistry (IUPAC) naming conventions for coordination compounds involve a systematic approach to naming complex chemical structures based on their composition and structure. The central principles behind these conventions include the following:

• Identify the central metal and its oxidation state, which is given in Roman numerals within parentheses.
• Name any anionic ligands first, followed by neutral ligands, and use specific names for each type of ligand (e.g., ammine for NH3, aqua for H2O).
• If present, name the central metal. For anionic complexes, use the suffix '-ate' on the metal's name.
• Specify the number of each type of ligand by using appropriate prefixes (mono-, di-, tri-, etc.).
• Follow the entire ligand-metal assembly by the counterion, if any.

In the exercise given, by following these rules, compounds were named systematically to reflect the central metal, the ligands surrounding it, their count, and the overall charge on the compound. These conventions ensure uniformity and clarity in communicating complex chemical information.