Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The number of bridging CO ligand(s) and Co-Co bond(s) in \(\mathrm{Co}_{2}(\mathrm{CO})_{8}\), respectively are:[Main Jan. \(\left.11,2019(\mathrm{II})\right]\) (a) 2 and 1 (b) 2 and 0 (c) 0 and 2 (d) 4 and 0

Step-by-Step Solution

Answer

(a) 2 bridging CO ligands and 1 Co-Co bond.

Step 1: Understanding the Structure

The compound given is \(\mathrm{Co}_2(\mathrm{CO})_8\), known as dicobalt octacarbonyl. It contains two cobalt metal centers coordinated with a total of eight carbonyl (CO) ligands.

Step 2: Identifying Bridging CO Ligands

In \(\mathrm{Co}_2(\mathrm{CO})_8\), there are typically two structures: a staggered conformation with two bridging CO ligands and an eclipse conformation. Here we focus on the more common staggered conformation which features 2 bridging CO ligands.

Step 3: Counting Co-Co Bonds

In \(\mathrm{Co}_2(\mathrm{CO})_8\), the two cobalt atoms are directly bonded to each other. This direct bond constitutes a single Co-Co bond in the structure.

Step 4: Concluding the Number of Ligands and Bonds

Based on the above analyses, \(\mathrm{Co}_2(\mathrm{CO})_8\) has 2 bridging CO ligands and 1 Co-Co bond. Thus, the correct answer is (a) 2 and 1.

Key Concepts

Bridging Ligands

In coordination chemistry, bridging ligands play a crucial role by connecting two or more metal centers in a coordination complex. These ligands help stabilize complex structures and often influence their reactivity and properties.
For example, in the dicobalt octacarbonyl compound, \(\mathrm{Co}_2(\mathrm{CO})_8\), there are CO ligands that can act as bridging ligands. This means that some of the carbonyl ligands span between the two cobalt metal centers, forming bridges.
Bridging ligands are highly versatile and can include atoms like oxygen, nitrogen, sulfur, and a variety of carbon-based ligands. Their presence affects both the stereochemistry and the function of the complex.
Understanding the role of bridging ligands allows chemists to predict and manipulate the properties of coordination compounds effectively. They are a key component of multi-metallic catalyst systems used in industrial processes.

Coordination Compounds

Coordination compounds are complex molecules consisting of a central metal atom or ion surrounded by molecules or anions, known as ligands. These ligands are bound to the metal center through coordinate covalent bonds.
The concept becomes particularly intriguing in the case of complex structures involving multiple metal atoms, such as the compound \(\mathrm{Co}_2(\mathrm{CO})_8\). This is known as a coordination cluster, where the metal-metal bonds and bridging ligands play a significant role in holding the structure together.
In coordination chemistry, these complexes are written in a specific notation that reflects their composition and the arrangement of ligands around the metal center. Recognizing the arrangement and the types of ligands involved is important for understanding properties like reactivity, color, and magnetic behavior.
Coordination complexes are essential in many areas of chemistry, including catalysis, materials science, and bioinorganic chemistry, where they have applications in drug development and enzyme function.

Metal-Metal Bonds

Metal-metal bonds are a fascinating aspect of coordination chemistry, particularly in metal cluster compounds where two or more metal atoms are directly bonded. These bonds can significantly affect the chemical and physical properties of the compound.
In dicobalt octacarbonyl, \(\mathrm{Co}_2(\mathrm{CO})_8\), the cobalt atoms form a direct bond. This bond contributes to the overall stability of the structure. Metal-metal bonding can vary greatly in strength and type, from weak dative bonds to strong covalent metal-metal bonds, depending on the metals involved and their oxidation states.
The presence of metal-metal bonds in coordination compounds is crucial for understanding their reactivity, electronic configuration, and potential uses in areas like catalysis.
Studying these bonds helps chemists design and synthesize new compounds with desirable properties for various industrial and research applications.