Problem 60 - A Complete Resource Book in Chemistry for JEE Main

Question

The oxidation state of \(\mathrm{Mo}\) in its oxo-complex species \(\left[\mathrm{Mo}_{2} \mathrm{O}_{4}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}\) is (a) \(+2\) (b) \(+3\) (c) \(+4\) (d) \(+5\)

Step-by-Step Solution

Answer

The oxidation state of Mo is +3.

Step 1: Understanding the Complex

The given complex is \( \left[\mathrm{Mo}_{2} \mathrm{O}_{4}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-} \). It consists of two molybdenum (Mo) atoms, four oxygen (O) atoms, two ethylene (\(\mathrm{C}_{2} \mathrm{H}_{4}\)) ligands, and two water (\(\mathrm{H}_{2} \mathrm{O}\)) ligands.

Step 2: Assigning Known Oxidation States

Oxygen typically has an oxidation state of \(-2\). Both \(\mathrm{C}_{2} \mathrm{H}_{4}\) (ethylene) and \(\mathrm{H}_{2} \mathrm{O}\) (water) are neutral ligands, contributing \(0\) to the overall charge of the complex.

Step 3: Setting Up the Equation

Let Mo have an oxidation state of \(x\). The overall charge of the complex is \(-2\). We can set up the equation representing the total charge as follows: \[ 2x + 4(-2) = -2 \]

Step 4: Solving for Oxidation State

Simplify the equation: \(2x - 8 = -2\). Add \(8\) to both sides to get \(2x = 6\). Divide by \(2\) to find \(x = 3\).

Step 5: Conclusion

The oxidation state of each Mo atom in the complex is \(+3\).

Key Concepts

Oxo-Complexes

Oxo-complexes are fascinating structures in coordination chemistry where a metal atom is bonded to one or more oxygen atoms. These complexes are quite prevalent in various catalytic and biological processes. The term "oxo" refers to the presence of oxygen atoms that are often bound to the metal center through a double bond, depicted as M=O. Oxo-groups are particularly influential in terms of the electronic properties of the complex. They can influence the redox potential and stability, often making the complex more rigid.

In our example of an oxo-complex \[\left[\mathrm{Mo}_{2} \mathrm{O}_{4}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}\] the molybdenum atoms are bonded to oxygen atoms, which significantly affects the molecule's reactivity. Oxo-complexes like this play a crucial role in molybdenum chemistry and broader applications, such as in oxygen transfer reactions.

Molybdenum Chemistry

Molybdenum is a transition metal situated in group 6 of the periodic table, known for its variable oxidation states ranging from \(-2\) to \(+6\). It plays an essential role in a variety of chemical and biological systems, not least in the form of complexes. Molybdenum is a key component in many enzymes, particularly those involved in oxygen transfer.

• Molybdenum oxo-complexes are involved in significant catalytic processes.
• They exhibit interesting redox behavior crucial to industrial and environmental chemistry.

In the given oxo-complex\[\left[\mathrm{Mo}_{2} \mathrm{O}_{4}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}\] molybdenum displays an oxidation state of \(+3\). Understanding the oxidation state is vital, as it influences reactivity and stability of the complex, providing insights into how such complexes can be synthesized and manipulated for desired reactions.

Ligand Coordination Chemistry

Ligand coordination chemistry is central to understanding complex formation in transition metals. Ligands are molecules or ions that bind to a central metal atom, forming a coordination complex. The interaction between ligands and metal ions dramatically determines the structure and function of the complex.

In the complex \(\left[\mathrm{Mo}_{2} \mathrm{O}_{4}\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2-}\) ethylene (\(\mathrm{C}_{2} \mathrm{H}_{4}\)) and water (\(\mathrm{H}_{2} \mathrm{O}\)) are neutral ligands. This means they do not contribute to the overall charge of the complex but help determine its geometry and reactivity:

• Neutral ligands like ethylene help stabilize the complex without altering its charge.
• Water molecules can participate in hydrogen bonding, potentially affecting solubility and additional reactions.

By serving different purposes, ligands influence the oxidation state of the metal and the overall structure, aiding in fine-tuning the complex for specific applications.