Problem 36 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) hexaammineiron(II) nitrate (b) tetraaquadibromochromium(III) perchlorate (c) ammonium hexachloropalladate(IV) (d) diammineoxolatonickel(II) (e) Hexaamminemolybdenum(III) tetrachlorocuprate(II)

Step-by-Step Solution

Answer

(a) \([Fe(NH3)_6] (NO3)_2\) (b) \([Cr(H2O)_4Br_2] (ClO4)_3\) (c) \((NH4)_2 [PdCl_6]\) (d) \([Ni(NH3)_2(C2O4)]\) (e) \([Mo(NH3)_6] [CuCl_4]_2\)

Step 1: Identify the components

In this compound, we have a central metal ion of iron (Fe) with an oxidation state of +2, the ligand is ammine (NH3) which has a coordination number of 6, and the counterion is nitrate (NO3^-).

Step 2: Write the formula

Now we can write the formula as: \([Fe(NH3)_6] (NO3)_2\) (b) tetraaquadibromochromium(III) perchlorate

Step 1: Identify the components

Here, we have a central metal ion of Chromium (Cr) with an oxidation state of +3, the ligands are aqua (H2O) with a coordination number of 4, and bromo (Br^-) with a coordination number of 2. The counterion is perchlorate (ClO4^-).

Step 2: Write the formula

The formula for this compound is: \([Cr(H2O)_4Br_2] (ClO4)_3\) (c) ammonium hexachloropalladate(IV)

Step 1: Identify the components

In this compound, the central metal ion is palladium (Pd) with an oxidation state of +4, the ligand is chloro (Cl^-) with a coordination number of 6, and the counterion is ammonium (NH4^+).

Step 2: Write the formula

The formula for this compound is: \((NH4)_2 [PdCl_6]\) (d) diammineoxolatonickel(II)

Step 1: Identify the components

Here, we have a central metal ion of nickel (Ni) with an oxidation state of +2, and the ligands are ammine (NH3) with a coordination number of 2, and oxolato (C2O4^2-) with a coordination number of 1.

Step 2: Write the formula

The formula for this compound is: \([Ni(NH3)_2(C2O4)]\) (e) Hexaamminemolybdenum(III) tetrachlorocuprate(II)

Step 1: Identify the components

In this compound, we have a central metal ion of molybdenum (Mo) with an oxidation state of +3, the ligand is ammine (NH3) with a coordination number of 6. The counterion is tetrachlorocuprate(II) \([CuCl_4]^{2-}\).

Step 2: Write the formula

The formula for this compound is: \([Mo(NH3)_6] [CuCl_4]_2\)

Key Concepts

Coordination Chemistry

Coordination chemistry is a fascinating branch of chemistry focusing on complex structures formed by transition metals and ligands. At the core of coordination compounds is a central metal ion. This metal ion is typically surrounded by molecules or ions known as ligands. These ligands form what we call a coordination sphere.

A key feature of coordination compounds is their unique geometries and binding characteristics, which vary based on the types of ligands and metals. This chemistry helps us understand many natural and synthetic processes.

• Found in biological systems (e.g., hemoglobin).
• Applications in medicine, such as contrast agents.
• Catalysts in industrial processes.

Understanding the fundamental principles of coordination chemistry provides insight into the structural and reactive properties of these critical compounds.

Ligands

Ligands are molecules or ions that donate a pair of electrons to the central metal atom, creating a coordination bond. These are crucial in determining the properties and reactivity of coordination complexes.

Ligands can be categorized based on:

• Charge: Neutral (e.g., H₂O, NH₃) or anionic (e.g., Cl^-, Br^-).
• Number of donor atoms: Monodentate (single donor atom, e.g., NH₃), bidentate (two donor atoms, e.g., C₂O₄^2-), or polydentate (more than two, e.g., EDTA).

The nature and number of ligands impact the geometry around the metal center and influence the compound's overall stability and chemical behavior. Ligands thus play a pivotal role in shaping coordination chemistry.

Oxidation States

Oxidation states in coordination compounds are vital for identifying the charge of the metal center and predicting the chemical reactivity. Each metal has a specific oxidation state, dictated by the number of ligands and the type of interactions within the coordination sphere.

To determine the oxidation state:

• Sum the charges of the ligands and the counterions.
• Use this sum to balance the overall charge of the compound.

If a metal in a complex has more electrons than its elemental form, it has a negative oxidation state. For fewer electrons, it has a positive oxidation state. Understanding oxidation states helps us predict how the complex will undergo various chemical transformations, providing insight into the compound's potential behavior in reactions.

Coordination Number

The coordination number in coordination chemistry describes the number of ligand donor atoms bonded to the central metal ion. This is fundamental in determining the geometry and stability of the complex.

Coordination number can vary:

• 4: Often results in tetrahedral or square planar geometries.
• 6: Commonly leads to an octahedral arrangement.
• Bidentate and polydentate ligands: These can increase the effective coordination number without changing the geometry.

By identifying the coordination number, chemists can predict the structure, reactivity, and properties of these complexes in various environments. This knowledge aids in the synthesis and application of coordination compounds in both laboratory and industrial settings.