Carbon monoxide (CO) forms bonds to a variety of metals and...

Carbon monoxide (CO) forms bonds to a variety of metals and metal ions. Its ability to bond to iron in hemoglobin is the reason that $\mathrm{CO}$ is so toxic. The bond carbon monoxide forms to metals is through the carbon atom: $$\mathbf{M}-\mathbf{C} \equiv \mathbf{O}$$ a. On the basis of electronegativities, would you expect the carbon atom or the oxygen atom to form bonds to metals? b. Assign formal charges to the atoms in CO. Which atom would you expect to bond to a metal on this basis? c. In the MO model, bonding MOs place more electron density near the more electronegative atom. (See the HF molecule in Figs. $4-54$ and $4-55 .$ ) Antibonding MOs place more electron density near the less electronegative atom in the diatomic molecule. Use the MO model to predict which atom of carbon monoxide should form bonds to metals.

Carbon monoxide (CO) forms bonds to a variety of metals and metal ions. Its ability to bond to iron in hemoglobin is the reason that $\mathrm{CO}$ is so toxic. The bond carbon monoxide forms to metals is through the carbon atom:
$$\mathbf{M}-\mathbf{C} \equiv \mathbf{O}$$
a. On the basis of electronegativities, would you expect the carbon atom or the oxygen atom to form bonds to metals?
b. Assign formal charges to the atoms in CO. Which atom would you expect to bond to a metal on this basis?
c. In the MO model, bonding MOs place more electron density near the more electronegative atom. (See the HF molecule in Figs. $4-54$ and $4-55 .$ ) Antibonding MOs place more electron density near the less electronegative atom in the diatomic molecule. Use the MO model to predict which atom of carbon monoxide should form bonds to metals.

Key Concepts

Formal Charges

Formal charge is a bookkeeping tool used to assess the distribution of electrons in a molecule, calculated by comparing the number of valence electrons in an isolated atom to the number assigned to the atom in the molecule's Lewis structure. This helps determine the most stable electron configuration and the likely sites of reactivity, including predicting which atom might preferentially interact with a metal center based on having a more negative charge.

Molecular Orbital Theory

Molecular orbital (MO) theory explains the bonding in molecules in terms of the combination of atomic orbitals to form delocalized molecular orbitals that extend over the entire molecule. This theory accounts for electron density distribution in bonding and antibonding orbitals, allowing predictions about the reactivity and bonding sites of atoms based on where electron density is concentrated.

Electronegativity

Electronegativity is a measure of an atom's ability to attract electron density towards itself. In the context of bonding, a more electronegative atom will tend to hold electrons more tightly, which influences how atoms interact within a molecule or with a metal, often determining the polarity of bonds and the sites of electrophilic or nucleophilic attack.

Metal-Ligand Bonding

Metal-ligand bonding involves the interaction between a metal atom or ion and a ligand that can donate electron density. The nature of these bonds is influenced by the electronic properties of both the metal and the ligand. Factors such as electronegativity, formal charges, and orbital overlap (as described by MO theory) determine which part of a ligand is most likely to coordinate with the metal, thus affecting the overall stability and reactivity of the complex.

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