Question

Give the formula of each of these coordination compounds formed with \(\mathrm{Pt}^{2+}\) (a) Two ammonia molecules and two bromide ions (b) One ethylenediamine molecule and two nitrite ions, \(\mathrm{NO}_{2}^{-}\) (c) One chloride ion, one bromide ion, and two ammonia molecules

Short answer

(a) \( [\mathrm{Pt(NH_3)_2(Br)_2}] \), (b) \( [\mathrm{Pt(en)(NO_2)_2}] \), (c) \( [\mathrm{Pt(NH_3)_2(Cl)(Br)}] \).

Step-by-step solution

Understanding Coordination Compounds

Coordination compounds consist of a central metal ion surrounded by molecules or ions called ligands. The metal ion forms coordinate bonds with ligands, which donate electron pairs.

Writing Formula for (a)

The compound has \ \( \mathrm{Pt^{2+}} \) ion, two ammonia molecules (\( \mathrm{NH_3} \)), and two bromide ions (\( \mathrm{Br^-} \)). Ammonia is a neutral ligand, and bromide is a monodentate anionic ligand. The coordination compound will be represented as \( [\mathrm{Pt(NH_3)_2(Br)_2}] \).

Writing Formula for (b)

The compound has \ \( \mathrm{Pt^{2+}} \), one ethylenediamine molecule (en, a bidentate neutral ligand), and two nitrite ions (\( \mathrm{NO_2^-} \)). The coordination compound is \( [\mathrm{Pt(en)(NO_2)_2}] \).

Writing Formula for (c)

The compound contains \ \( \mathrm{Pt^{2+}} \), one chloride ion (\( \mathrm{Cl^-} \)), one bromide ion (\( \mathrm{Br^-} \)), and two ammonia molecules (\( \mathrm{NH_3} \)). Therefore, the coordination compound will be \( [\mathrm{Pt(NH_3)_2(Cl)(Br)}] \).

Key concepts

Metal Ions

In coordination chemistry, metal ions like \( \mathrm{Pt}^{2+} \) play a crucial role as the central atoms around which ligands arrange themselves. The central metal ion, with its positive charge, attracts ligands, which are molecules or ions that have an available pair of electrons to donate. This attraction forms a coordination sphere, fundamentally altering the properties of the central ion. Metals can exhibit various oxidation states, which affect their ability to bind with ligands. In this exercise, we see \( \mathrm{Pt}^{2+} \), indicating platinum in a +2 oxidation state. This means platinum has lost two electrons, allowing it to form stronger bonds with the donating ligands.Understanding these metal ions helps in predicting the geometry and chemical behavior of the resulting coordination compound. Each ion influences the overall structure and stability of the compound, determining the number and type of ligands that can associate to form a stable complex.

Ligands in Chemistry

Ligands are chemical entities capable of donating electron pairs to a metal ion, forming a coordination bond. They are key players in creating the framework of a coordination compound, essentially determining its composition and properties. Different types of ligands include:

• Monodentate ligands: Bind through a single pair of electrons. For example, ammonia \( \mathrm{NH_3} \) and bromide \( \mathrm{Br^-} \), both widely seen in coordination chemistry.
• Bidentate ligands: Have two points of attachment, like ethylenediamine ("en").
• Polydentate ligands: Capable of forming multiple bonds with the central metal ion.

In this exercise, ligands like ammonia and bromide ions may act individually by binding through one atom, while ethylenediamine secures two coordination sites on \( \mathrm{Pt}^{2+} \), forming more stable and often spatially complex structures. Understanding ligand behavior aids in constructing the coordination complexes with correct formulas.

Chemical Formulas

Chemical formulas in coordination chemistry are precise representations of the composition and structure of the compound. Writing them accurately is crucial for reflecting the interactions within the compound, including the nature and arrangement of ligands around the central metal ion.In a chemical formula:

• Ligands are generally placed in square brackets along with the central metal ion, to denote the coordination sphere.
• The order of listing ligands can vary but often follows some convention, like alphabetic when possible.
• Neutral ligands like ammonia \( (\mathrm{NH_3}) \) are represented without a charge, while charged ligands like bromide \( (\mathrm{Br^-}) \) carry their ionic charge, contributing to the overall charge balance.

For coordination complexes given in the exercise, such as \([\mathrm{Pt(NH_3)_2(Br)_2}]\), the formula accurately presents two ammonia molecules and two bromide ions coordinated around the \( \mathrm{Pt}^{2+} \). The notation reflects both the stoichiometry and the spatial arrangement of the ligands, which is essential for understanding the coordination chemistry and potential reactivity of the compounds.