Question

Write equations for the stepwise formation of each of the following complex ions. a. $\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$ b. $\mathrm{V}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3{}^{3-}$

Short answer

The stepwise formation equations for the given complex ions are: a. For $\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$: 1. ${\mathrm{Ni}}^{2+}+{\mathrm{CN}}^{-}\to {\mathrm{NiCN}}^{+}$ 2. ${\mathrm{NiCN}}^{+}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_2$ 3. $\mathrm{Ni}(\mathrm{CN}{)}_2+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_3^{-}$ 4. $\mathrm{Ni}(\mathrm{CN}{)}_3^{-}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$ b. For $\mathrm{V}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3{}^{3-}$: 1. ${\mathrm{V}}^{3+}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to {\mathrm{VC}}_2{\mathrm{O}}_4^{+}$ 2. ${\mathrm{VC}}_2{\mathrm{O}}_4^{+}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to \mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2^{-}$ 3. $\mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2^{-}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to \mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_3^{3-}$

Step-by-step solution

Identify metal ions and ligands for both complex ions

For the given complex ions, we can identify the metal ions and ligands as follows: a. In $\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$: Metal ion: ${\mathrm{Ni}}^{2+}$ Ligand: ${\mathrm{CN}}^{-}$ (cyanide ion) b. In $\mathrm{V}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3{}^{3-}$: Metal ion: ${\mathrm{V}}^{3+}$ Ligand: ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ (oxalate ion)

Write stepwise formation equations for $\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$

We will now show the stepwise formation of the complex ion $\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$ by adding cyanide ions to the nickel(II) ion: 1. ${\mathrm{Ni}}^{2+}+{\mathrm{CN}}^{-}\to {\mathrm{NiCN}}^{+}$ 2. ${\mathrm{NiCN}}^{+}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_2$ 3. $\mathrm{Ni}(\mathrm{CN}{)}_2+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_3^{-}$ 4. $\mathrm{Ni}(\mathrm{CN}{)}_3^{-}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$

Write stepwise formation equations for $\mathrm{V}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3{}^{3-}$

Similarly, we will show the stepwise formation of the complex ion $\mathrm{V}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3{}^{3-}$ by adding oxalate ions to the vanadium(III) ion: 1. ${\mathrm{V}}^{3+}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to {\mathrm{VC}}_2{\mathrm{O}}_4^{+}$ 2. ${\mathrm{VC}}_2{\mathrm{O}}_4^{+}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to \mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2^{-}$ 3. $\mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2^{-}+{\mathrm{C}}_2{\mathrm{O}}_4^{2-}\to \mathrm{V}({\mathrm{C}}_2{\mathrm{O}}_4{)}_3^{3-}$ These are the stepwise formation equations for the given complex ions.

Key concepts

Stepwise Formation of Complex Ions

Understanding how complex ions form involves looking at the step-by-step addition of ligands to a metal ion. In the exercise, this is shown through stepwise formation equations, illustrating each stage of the process.

For example, when forming $$\mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$$, cyanide ions (the ligands) are added progressively to the nickel (Ni²⁺) ion. Each step adds one ligand, changing the structure of the metal complex:

• ${\mathrm{Ni}}^{2+}+{\mathrm{CN}}^{-}\to {\mathrm{NiCN}}^{+}$
• ${\mathrm{NiCN}}^{+}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_2$
• $\mathrm{Ni}(\mathrm{CN}{)}_2+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_3^{-}$
• $\mathrm{Ni}(\mathrm{CN}{)}_3^{-}+{\mathrm{CN}}^{-}\to \mathrm{Ni}(\mathrm{CN}{)}_4^{2-}$

This method helps to understand how complex ions incrementally grow by binding additional ligands.

Understanding Metal Ions

Metal ions play a central role in the formation of coordination compounds. In the exercise, metal ions like ${\mathrm{Ni}}^{2+}$ and ${\mathrm{V}}^{3+}$ act as the core to which ligands attach.

Metal ions are positively charged particles that attract negatively charged ligands. This electric attraction is what holds the ligands in place.

• The charge of the metal ion can influence the number and type of ligands it can bind with.
• The properties of the metal ion, such as its size and electronic configuration, affect the stability and shape of the coordination compound.

Understanding these properties helps predict how metal ions will interact with ligands to form various coordination compounds.

Role of Ligands in Complex Ion Formation

Ligands are molecules or ions that donate a pair of electrons to a metal ion, forming a coordination bond. In the exercise, ligands like ${\mathrm{CN}}^{-}$ (cyanide) and ${\mathrm{C}}_2{\mathrm{O}}_4^{2-}$ (oxalate) play crucial roles in complex ion formation.

These ligands can vary greatly in structure and charge, influencing the properties of the resulting coordination compound:

• Ligands can be mono-, bi-, or polydentate, meaning they can connect to the metal ion at one or more points.
• The strength and type of bond formed with the metal ion affect the overall stability and reactivity of the complex.
• The choice of ligands can significantly alter the physical properties of the complex, such as color and magnetic behavior.

This versatility makes ligands essential components in the chemistry of coordination compounds.

Coordination Compounds Overview

Coordination compounds are unique chemical structures formed when ligands bind to a central metal ion. This interaction forms complex ions as seen in the exercise examples.

These compounds are integral to many chemical processes and applications:

• Coordination compounds can exhibit various geometric structures, such as octahedral or tetrahedral, depending on the type and number of ligands.
• They play significant roles in biological systems, such as hemoglobin's function in oxygen transport, where iron acts as the metal center.
• Their varied structures make them useful in fields like catalysis and materials science.

Understanding coordination compounds involves recognizing how the combination of metal ions and ligands leads to diverse chemical behaviors and applications.