Among the following , metal carbonyls, the C-O bond is strongest :

Options

A. `[Mn(CO)_(6)]^(+)`
B. `[Cr(CO)_(6)]`
C. `[V(CO)_(6)]^(-)`
D. `[Ti(CO)_(6)]^(2-)`

Answer

To determine which metal carbonyl has the strongest C-O bond among the given options, we can follow these steps:

### Step 1: Identify the Metal Carbonyls
Let's assume we have the following metal carbonyls to compare:
- Mn(CO)6^+
- Cr(CO)6
- V(CO)6^−
- Ti(CO)6^2−

### Step 2: Determine the Isoelectronic Nature
All these complexes are isoelectronic, meaning they have the same number of electrons. This is important because it allows us to compare their properties directly without considering differences in electron count.

### Step 3: Analyze the Oxidation States
- Mn is in the +1 oxidation state.
- Cr is in the 0 oxidation state.
- V is in the -1 oxidation state.
- Ti is in the -2 oxidation state.

### Step 4: Understand the Relationship Between Charge and Back Bonding
The key concept here is that the more positive the charge on the metal complex, the less back bonding occurs with the CO ligands. Back bonding involves the donation of electron density from the metal d-orbitals to the π* orbitals of CO, which weakens the C-O bond.

### Step 5: Relate Charge to CO Bond Strength
- A complex with a higher positive charge (like Mn(CO)6^+) will have less back bonding, resulting in a higher bond order for the C-O bond.
- Conversely, complexes with negative charges (like Ti(CO)6^2−) will have more back bonding, which weakens the C-O bond.

### Step 6: Rank the Metal Carbonyls by CO Stretching Frequency
The CO stretching frequency is directly proportional to the bond order and thus the bond strength. Therefore, we can rank the complexes based on their expected CO stretching frequencies:
1. Mn(CO)6^+ (highest frequency)
2. Cr(CO)6
3. V(CO)6^−
4. Ti(CO)6^2− (lowest frequency)

### Step 7: Conclusion
Since Mn(CO)6^+ has the highest CO stretching frequency, it also has the highest bond order and therefore the strongest C-O bond among the given metal carbonyls.

### Final Answer
The metal carbonyl with the strongest C-O bond is **Mn(CO)6^+**.

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