Question

What is the formula, including the charge, for each of the following complexes? (a) An iron(III) complex with six water ligands (b) A nickel(II) complex with two ethylenediamine and two bromide ligands (c) A platinum(II) complex with two chloride and two ammonia ligands

Short answer

(a) \\[\text{[Fe(H}_2 \text{O})_6]^{3+}\\], (b) \\[\text{[Ni(en})_2 \text{Br}_2]}\\], (c) \\[\text{[Pt(NH}_3\text{)}_2 \text{Cl}_2]}\\].

Step-by-step solution

Understand the Complex Formation

Complexes consist of a central metal atom surrounded by ligands, which are atoms or groups of atoms that can donate a pair of electrons to the metal. Iron(III), nickel(II), and platinum(II) indicate that the metal ions have a charge of +3, +2, and +2 respectively.

Determine the Ligands and their Charges

For (a), water (H₂O) is a neutral ligand. For (b), ethylenediamine (en) is a neutral ligand and bromide (Br⁻) has a charge of -1. For (c), both chloride (Cl⁻) and ammonia (NH₃) are neutral ligands.

Construct Each Complex Formula

(a) The iron(III) complex with six water ligands is \[{\text{[Fe(H}_2 \text{O})_6]}^{3+}\], since water is neutral.(b) The nickel(II) complex with two ethylenediamine (en) and two bromide ligands is \[{\text{[Ni(en})_2 \text{Br}_2]}\]. Nickel has a charge of 2+, and the two bromide ions total -2, balancing to a neutral complex.(c) The platinum(II) complex with two chloride and two ammonia ligands is \[{\text{[Pt(NH}_3\text{)}_2 \text{Cl}_2]}\]. The Pt has a 2+ charge, and each chloride is -1, balancing the charge to zero.

Summarize Each Complex Formula with Charges

(a) \[{\text{[Fe(H}_2 \text{O})_6]}^{3+}\](b) \[{\text{[Ni(en})_2 \text{Br}_2]}\](c) \[{\text{[Pt(NH}_3\text{)}_2 \text{Cl}_2]}\]

Key concepts

Ligands

In coordination chemistry, ligands play a pivotal role. These are atoms or molecules that bind to the central metal atom or ion to form a coordination complex. Ligands function by donating one or more pairs of electrons to the central metal, forming what is known as a "coordinate covalent bond."
Types of ligands can vary based on the number of donor atoms they contain. Some common categories include:

• Monodentate Ligands: These ligands have only one donor atom, such as water (H₂O) and chloride (Cl⁻).
• Bidentate Ligands: These have two donor atoms that can bind to the metal, like ethylenediamine (en).
• Polydentate Ligands: They contain multiple donor sites, allowing them to "wrap around" the metal ion.

Water and ammonia (NH₃) are neutral ligands, while bromide (Br⁻) and chloride (Cl⁻) are charged ligands, contributing to the complex's overall charge.

Coordination Chemistry

Coordination chemistry deals with the study of complexes comprising a central metal and surrounding ligands. The central metal ion can bind to several ligands due to its ability to accept electron pairs. This subject provides insights into the formation, structure, and properties of these complexes.
The central concept here is the coordinate covalent bond, which involves the sharing of electrons between the ligand and the central atom. This bond is formed when a ligand donates an electron pair to the metal ion. The strength and stability of coordination complexes depend on several factors:

• The nature and charge of the metal ion
• The type and number of ligands
• The size of the metal ion and ligands

The study of coordination chemistry is significant as it leads to the development of materials with diverse applications, such as catalysts, dyes, and drugs for therapeutic uses.

Chemical Formulas

Chemical formulas for coordination complexes convey information about the composition and arrangement of the atoms within the complex. When constructing such formulas, it is important to reflect the number of each type of ligand and the charge on the complex.

• Start with the central metal and its oxidation state, which determines the total number of electrons it can accept.
• Next, list the ligands: within the formula, it is common to enclose the entire complex in square brackets.
• Indicate the charge of the entire complex outside the brackets. For instance, the formula \[\text{[Fe(H}_2 \text{O})_6]^{3+}\] shows that six neutral water molecules surround an iron(III) ion, resulting in an overall +3 charge.

Understanding the arrangement of ligands and metal ions in these formulas is crucial for predicting the properties and reactivity of the complexes.