Problem 30 - A Complete Resource Book in Chemistry for JEE Main

Question

The formula of a carbonyl complex of cobalt (CO) \(\mathrm{Co}-\mathrm{Co}(\mathrm{CO})_{n}\) in which there is single covalent \(\mathrm{CO}-\) \(\mathrm{CO}\) bond is (a) \(\mathrm{Co}_{2}(\mathrm{CO})_{8}\) (b) \(\mathrm{Co}_{2}(\mathrm{CO})_{10}\) (c) \(\mathrm{Co}(\mathrm{CO})_{4}\) (d) \(\mathrm{Co}(\mathrm{CO})_{8}\)

Step-by-Step Solution

Answer

The correct formula is \( \mathrm{Co}_2(\mathrm{CO})_8 \).

Step 1: Understanding the Problem

We need to determine the correct chemical formula for a carbonyl complex of cobalt that contains a single covalent Co-Co bond. This involves knowledge of chemical bonding and the possible structures of cobalt carbonyl compounds.

Step 2: Review of Cobalt Carbonyl Compounds

Cobalt carbonyl compounds like \( \mathrm{Co}_2(\mathrm{CO})_8 \) and \( \mathrm{Co}_2(\mathrm{CO})_{10} \) can have Co-Co bonds. \( \mathrm{Co}(CO)_{n} \) would typically indicate mononuclear complexes without Co-Co bonds.

Step 3: Analysis of Options

We analyze each given structure:- \( \mathrm{Co}_2(\mathrm{CO})_8 \) is known to form a dimer with a Co-Co bond.- \( \mathrm{Co}_2(\mathrm{CO})_{10} \) is not a commonly possible structure.- \( \mathrm{Co}(CO)_4 \) suggests a mononuclear compound, hence no Co-Co bond.- \( \mathrm{Co}(CO)_8 \) also suggests a mononuclear compound, not feasible.

Step 4: Identifying the Correct Answer

By reviewing existing cobalt carbonyl complexes, \( \mathrm{Co}_2(\mathrm{CO})_8 \) is confirmed to have a single covalent Co-Co bond, differentiating it from the other provided options.

Key Concepts

Cobalt Compounds

Cobalt compounds, particularly those involving carbonyl ligands, have fascinating properties. Cobalt, a transition metal, often forms compounds with carbon monoxide, known as carbonyl complexes. These special compounds are studied due to their unique bond formations and chemical bonding properties. One such example is the compound \( \text{Co}_2(\text{CO})_8 \), which contains a direct cobalt-to-cobalt bond. This compound demonstrates how cobalt can pair with carbon monoxide to form complex structures and provide extra stability through these interactions.

• Cobalt carbonyls are interesting for their ability to create various bond configurations.
• They are often utilized in catalysis and industrial applications.
• Their stability makes them a topic of study for learning about transition metal behaviors.

Chemical Bonding

Chemical bonding is a critical concept to understand when studying cobalt carbonyl compounds. Bonding explains how atoms stick together to form molecules. In the case of cobalt carbonyl complexes, chemical bonding helps us grasp how metal centers bond to ligands like carbon monoxide.

Metal-Ligand Interaction

This interaction is largely due to covalent bonding, where orbitals from the metal overlap with orbitals from the ligand:

• Carbon monoxide serves as a ligand, donating electron pairs to the cobalt atom.
• The cobalt, in turn, back-donates electron density into antibonding orbitals of the CO molecule, stabilizing the complex.

By understanding these chemical bonds, scientists can predict the structure and properties of complex compounds.

Covalent Bonds

Covalent bonds form when two atoms share electrons, creating a stable balance of attractive and repulsive forces between atoms. In the case of cobalt carbonyl complexes, covalent bonds are crucial as they lead to the formation of the structure and properties of the compound.

Cobalt-Carbonyl Bonding

The bonds between cobalt and carbon monoxide in these complexes are examples of metal-to-ligand covalent bonds:

• Covalent bonds are not only formed between Co and CO, but also between two cobalt atoms in some complexes.
• These bonds allow the complex to maintain stability through electron sharing.
• The Co-Co bond, in particular, highlights the unique ability of cobalt to engage in multiple bonding scenarios.

Understanding covalent bonding within cobalt complexes helps in predicting their reactivity and uses.

Complex Structures

Analyzing complex structures advances our understanding of chemistry, especially with transition metals like cobalt. Complexes such as \( \text{Co}_2(\text{CO})_8 \) illustrate how complex structures can form, revealing the versatility of cobalt as a central atom.

Diverse Arrangements

The structure of cobalt carbonyl complexes showcases several important aspects:

• Cobalt carbonyls can exhibit various shapes depending on the number of CO ligands.
• The presence of a direct Co-Co bond in some structures adds an additional layer of complexity.
• These diverse structures have implications in how the complexes interact with other substances and their potential applications.

By examining these structures, scientists discover more about coordination chemistry and the role of transition metals.