Problem 64 - Chemistry and Chemical Reactivity

Question

A platinum-containing compound, known as Magnus's green salt, has the formula \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{PtCl}_{4}\right]\) (in which both platinum ions are \(\mathrm{Pt}^{2+}\) ). Name the cation and the anion.

Step-by-Step Solution

Answer

Cation: tetraammineplatinum(II); Anion: tetrachloroplatinate(II).

Step 1: Identify the Cation

The cation in the compound is enclosed in the first set of square brackets: \( [\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}] \). This consists of the platinum ion \( \mathrm{Pt}^{2+} \) surrounded by four \( \mathrm{NH}_{3} \) (ammonia) ligands. The name for this cation is 'tetraammineplatinum(II)'.

Step 2: Identify the Anion

The anion is enclosed in the second set of square brackets: \( [\mathrm{PtCl}_{4}] \). This part contains the platinum ion \( \mathrm{Pt}^{2+} \) with four chloride ions. The name for this anion is 'tetrachloroplatinate(II)'.

Key Concepts

Complex Ions

In coordination chemistry, a complex ion is a central atom or ion that is bonded to a group of molecules or anions, known as ligands. These complex ions are essential in diverse chemical compounds and reactions. The central atom is often a transition metal, which can form multiple bonds with the ligands. This multi-bond property is due to their ability to donate and accept electrons, which stabilizes the structure of the entire compound.
Complex ions can carry a positive, negative, or neutral charge, depending on the combination of the metal ion and its ligands. For instance, in the exercise, the cation \([\mathrm{Pt}(\mathrm{NH}_{3})_{4}]^{2+}\) is a complex ion, where platinum acts as the central metal ion. This platinum ion is enveloped by four ammonia ligands, making it a complete tetrahedral configuration. Such configurations contribute to the ion's overall charge.
Understanding complex ions is crucial as they play a key role in the reactivity and color of the compounds. They are also involved in catalysis and various biochemical processes, like photosynthesis and respiration.

Transition Metals

Transition metals are a group of elements found in the center of the periodic table, famously known for their ability to form various oxidation states. Unlike elements that stick to a single oxidation state, transition metals like platinum, as seen in this example, can have multiple charges. This ability comes from unpaired d-electrons that can participate in chemical bonding.
Platinum, a transition metal, is a key player in the compound Magnus's green salt. It exhibits the oxidation state of +2 in both cation and anion as shown by \(\mathrm{Pt}^{2+}\).
These metals are incredibly versatile because they can interact with a variety of ligands, leading to the formation of complex ions. Their unique properties allow them to participate widely in not only coordination chemistry but in real-world applications, from catalysts in industrial processes to significant roles in biological systems and materials.

Chemical Nomenclature

Chemical nomenclature refers to the systematic naming of chemical compounds. It allows scientists and students to communicate unambiguously. In coordination chemistry, the naming follows specific rules outlined by IUPAC.
Firstly, in naming a complex ion, the ligands are identified first followed by the central metal ion. Ligands like ammonia (\(\mathrm{NH}_3\)) in the earlier example are named before the metal. When multiple identical ligands are present, prefixes like 'di-' or 'tetra-' are used to indicate the number of such ligands. Thus, the cation \([\mathrm{Pt}(\mathrm{NH}_{3})_{4}]^{2+}\) is named 'tetraammineplatinum(II)'.
Secondly, the oxidation state of the metal within the complex ion is indicated in parentheses using Roman numerals. This important step helps in specifying the exact form of the metal in the compound, crucial for determining its chemical behavior.
Lastly, when it comes to the anion naming in complex ions, the suffix '-ate' is often added to the name of the metal, such as 'tetrachloroplatinate(II)', indicating a complex anion with chlorine as ligands.