Problem 49 - Chemistry and Chemical Reactivity

Question

Give the formula of the coordination complex formed from one \(\mathrm{Co}^{3+}\) ion, two ethylenediamine molecules, one water molecule, and one chloride ion. Is the complex neutral or charged? If charged, give the net charge on the ion.

Step-by-Step Solution

Answer

The formula is \( [\mathrm{Co(en)_2(H_2O)Cl}]^{2+}\); the complex is charged with a net charge of +2.

Step 1: Identify the Coordination Sphere

The coordination sphere consists of the central metal ion, which in this case is cobalt ( \(\mathrm{Co}^{3+}\)). It also includes the molecules and ions directly attached to the metal ion inside the brackets. These ligands are two ethylenediamine molecules, one water molecule, and one chloride ion.

Step 2: Determine the Formula of the Complex

Each ethylenediamine (en) is a bidentate ligand, so two en molecules provide 4 coordination sites. The water molecule (H2O) is monodentate, providing 1 coordination site, and the chloride ion (Cl⁻) provides 1 coordination site. Together with the cobalt ion, the formula for the complex becomes:\[[\mathrm{Co(en)_2(H_2O)Cl}]\] where 'en' represents ethylenediamine. Ethylenediamine is represented by en for simplicity.

Step 3: Determine the Charge of the Complex Ion

The ethylenediamine and water are neutral ligands, while the chloride ion carries a charge of -1. The metal ion is \(\mathrm{Co}^{3+}\). Therefore, the overall charge of the complex can be calculated as follows:\[\mathrm{Charge} = +3 - 1 = +2\]Thus, the complex has a net charge of +2.

Key Concepts

Co3+ ion

The cobalt ion (\( \mathrm{Co}^{3+} \)) is an essential part of many coordination complexes. In its +3 oxidation state, cobalt has a high positive charge, which greatly influences its ability to bind with various ligands, such as ethylenediamine and water. When an element like cobalt has a +3 charge, it has lost three electrons. This state is common in complex coordination chemistry as it allows cobalt to achieve different coordination numbers and form stable structures. Cobalt, as a transition metal, can form complexes with different ligands. This flexibility is due to its capability to accept both single- and multi-dentate ligands, adjusting its geometry according to the number and type of ligands. In the context of our given problem, cobalt enhances the stability and specific geometry of the formed coordination complex.

ethylenediamine ligand

Ethylenediamine, represented as 'en' in chemical equations, is a bidentate ligand. This means it can attach to the central metal ion at two coordination sites. The molecule itself is structured with two nitrogen atoms, each possessing a lone pair of electrons, making them capable of forming coordinate bonds with metal ions like \( \mathrm{Co}^{3+} \).Bidentate ligands, such as ethylenediamine, are particularly important in chemistry because they help form more stable complexes compared to monodentate ligands. These types of ligands can wrap around the metal ion, creating a chelate, which enhances the overall stability of the complex. In our exercise, two ethylenediamine molecules contribute significantly to the coordination sphere of cobalt, occupying four sites out of the total possible coordination spots around the metal ion. This plays a key role in the geometric configuration of the complex.

net charge

The net charge of a coordination complex is a crucial feature that defines its chemical behavior. It is the sum of the charges of the central metal ion and all its ligands. In the coordination complex involving \( \mathrm{Co}^{3+} \), two ethylenediamine molecules, a water molecule, and a chloride ion, understanding the net charge begins with analyzing each component individually:

• The \( \mathrm{Co}^{3+} \) ion itself contributes a charge of +3.
• Ethylenediamine and water are neutral, so they contribute no charge.
• The chloride ion adds a charge of -1.

To calculate the net charge of the entire complex, you sum these individual charges: \[\text{Net Charge} = (+3) + (0) + (-1) = +2\]Thus, the complex has a net charge of +2. This positive charge impacts how the complex will interact with other molecules and ions. A net charge often determines the solubility of the complex in various solvents and affects its reactivity in biochemical and industrial processes. Understanding and calculating net charge is essential for predicting these interactions and designing applications in coordination chemistry.