The common heptacity observed for coordination of C60 to a metal center is

Concept:

→ The coordination number of a metal center is determined by the number of ligands that can bind to it. In the case of C₆₀, it can act as a ligand by donating its π-electrons to the metal center, forming a coordination complex.

→ C₆₀ has a spherical structure with 60 carbon atoms arranged in a pattern of hexagons and pentagons, giving it a cage-like structure. It has 60 π-electrons that can participate in coordination to a metal center.

→ These π-electrons are delocalized over the entire molecule, making C₆₀ a good electron donor and capable of coordinating to metal ions.

→ When C₆₀ coordinates to a metal center, the metal ion can accept up to two π-electrons from each C₆₀ molecule. This is because each C₆₀ molecule has a total of 60 π-electrons, and the metal ion can accept up to two electrons from each of the 30 double bonds in C₆₀.

Explanation:

→ One example of a C₆₀ coordination complex with heptacoordinate metal center is [Ru(bpy)₃]₂(C₆₀), where bpy stands for 2,2'-bipyridine.

→ In this complex, the ruthenium(II) ion serves as the metal center, and the C₆₀ molecule coordinates to it through the π-electrons in the fullerene cage.

→ The heptacoordinate geometry is achieved by the coordination of three bipyridine ligands to the ruthenium center, each donating two nitrogen lone pairs, resulting in six coordination sites occupied.

→ The remaining coordination sites are occupied by two π-electrons from the C₆₀ molecule, with each double bond of the fullerene donating a pair of π-electrons to the ruthenium ion.

Overall, each C₆₀ molecule donates two π-electrons to the metal center, resulting in a heptacoordinate ruthenium(II) ion with a stable coordination complex. The [Ru(bpy)₃]₂(C₆₀) complex has been studied for its electrochemical and photochemical properties, demonstrating the ability of C₆₀ to act as a ligand and donate π-electrons to a metal center.

Conclusion:
Therefore, the common heptacity observed for coordination of C₆₀ to a metal center is 2, meaning that each C₆₀ molecule can coordinate to a metal center and donate up to two π-electrons. This results in a total of 14 π-electrons donated by each C₆₀ molecule to the metal center, forming a stable coordination complex.