Question

What is the systematic name for each of the following compounds? (a) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}\) (b) \(\operatorname{Cr}(\mathrm{CO})_{6}\) (c) \(\mathrm{K}_{3}\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (d) \(\left[\mathrm{Co}(\mathrm{en})_{2}\left(\mathrm{NH}_{3}\right) \mathrm{CN}\right] \mathrm{Cl}_{2}\)

Short answer

(a) Tetraamminecopper(II) sulfate; (b) Hexacarbonylchromium(0); (c) Potassium tris(oxalato)ferrate(III); (d) Diethylenediamineamminecyano cobalt(III) chloride.

Step-by-step solution

Name the Coordination Entity for Compound (a)

For compound (a), \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}\), the complex ion is \([\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+}\). Copper has a +2 oxidation state. The ligand \(\mathrm{NH}_3\) is ammonia and is named "ammine." Therefore, the coordination entity is named as tetraamminecopper(II).

Name the Anion for Compound (a)

The anion is sulfate (\(\mathrm{SO}_{4}^{2-}\)).

Combine Names for Compound (a)

Combine the coordination entity with the anion: Tetraamminecopper(II) sulfate.

Name the Compound (b)

For \(\operatorname{Cr}(\mathrm{CO})_{6}\), the ligand \(\mathrm{CO}\) is carbonyl and the complex is neutral, so we name the metal without modification. The compound is named hexacarbonylchromium(0).

Name the Coordination Entity for Compound (c)

For compound (c), \(\mathrm{K}_{3}\left[\mathrm{Fe}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}\right]\), identify \(\mathrm{Fe}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}^{3-}\). Oxalate \((\mathrm{C}_{2}\mathrm{O}_{4}^{2-})\) is a bidentate ligand. Iron has a +3 oxidation state. The complex is named as tris(oxalato)ferrate(III).

Name the Cation for Compound (c)

The cation is potassium (\(\mathrm{K}^{+}\)).

Combine Names for Compound (c)

Combine the cation with the coordination entity: Potassium tris(oxalato)ferrate(III).

Name the Coordination Entity for Compound (d)

For compound (d), \([\mathrm{Co}(\mathrm{en})_{2}(\mathrm{NH}_{3})\mathrm{CN}] \mathrm{Cl}_{2}\), \(\mathrm{en}\) is ethylenediamine, a bidentate ligand, and \(\mathrm{NH}_{3}\) and \(\mathrm{CN}^-\) are monodentate ligands. Cobalt has a +3 oxidation state. The coordination entity is named as diethylenediamineamminecyano cobalt(III).

Name the Anion for Compound (d)

The anion is chloride (\(\mathrm{Cl}_2\)).

Combine Names for Compound (d)

Combine the coordination entity with the anion: Diethylenediamineamminecyano cobalt(III) chloride.

Key concepts

Systematic Naming in Coordination Chemistry

Systematic naming in coordination chemistry helps us ensure we have a clear and standard way to describe complex compounds. This avoids confusion and makes communication easier across the scientific community.
In coordination compounds, the systematic name typically includes:

• The identity of the ligands around the central metal ion
• The oxidation state of the metal
• The structure and order of the compound

For example, a compound like \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}\) is named based on its coordination entity \([\mathrm{Cu}(\mathrm{NH}_3)_4]^{2+}\) and its sulfate anion. Each ligand, like \(\mathrm{NH}_3\), is given a specific name—in this case, "ammine." The metal's oxidation state is indicated by a Roman numeral following its name, like "Copper(II)."
This results in the full name: "tetraamminecopper(II) sulfate." This systematic approach helps identify exactly what each compound is composed of.

Understanding Ligands

Ligands play a major role in forming coordination complexes. A ligand is an ion or molecule that donates at least one pair of electrons to a central metal atom or ion.
The interactions between ligands and metals are essential for stability and the overall characteristics of the complex.
Here's how ligands are classified in coordination chemistry:

• Monodentate: Ligands that donate a single pair of electrons. Example – \(\mathrm{NH}_{3}\) (ammonia), \(\mathrm{CN}^-\) (cyano)
• Bidentate: Ligands that can donate two electron pairs. Example – \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\) (oxalate), \(\mathrm{en}\) (ethylenediamine)

These ligands form coordinate bonds with the metal center, impacting properties like stability and reactivity. For instance, in \(\mathrm{K}_{3}\left[\mathrm{Fe}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{3}\right]\), bidentate oxalate ligands create a stable chelate with the iron ion.

Determining Oxidation States

The oxidation state of the central metal in a coordination compound reveals valuable information about its electronic structure and reactivity.
It is typically a positive integer representing the number of electrons the metal has effectively "lost" to the surrounding ligands.
To determine the oxidation state:

• Assign a charge of 0 to neutral ligands like \(\mathrm{NH}_{3}\) or \(\mathrm{CO}\).
• Assign the known charge to ionic ligands, such as -2 for oxalate \((\mathrm{C}_2\mathrm{O}_4^{2-})\) or -1 for cyano \((\mathrm{CN}^-)\).
• Combine these with the overall charge of the complex to solve for the metal's oxidation state.

For instance, in \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+}\), \(\mathrm{NH}_3\) is neutral, and assigning these charges leads to understanding copper is in a +2 oxidation state.

Foundations of Coordination Chemistry

Coordination chemistry explores the structure and behavior of complexes formed between transition metals and ligands.
This field underscores the bond formation between metals, which often involve d-orbitals, and surrounding ligands.
Key aspects of coordination chemistry include:

• The coordination number, which is the count of ligand attachment points to the central metal, varying widely from 2 to 8 or more.
• The geometry of complexes, which can be linear, square planar, tetrahedral, octahedral, etc., based on coordination number and ligand type.
• Stability of complexes, influenced by the nature of the metal, the ligands, and the metal-ligand interactions.

An example is \(\operatorname{Cr}(\mathrm{CO})_{6}\), which is hexacoordinate and exhibits an octahedral geometry due to the symmetrical distribution of the carbonyl ligands. Understanding these aspects is crucial for predicting and controlling the chemical behavior of coordination compounds.