In the isoelectronic series of metal carbonyl, the CO bond strength is expected to increase in the o — Coordination Compounds Chemistry Question

💡 Solution & Explanation

Step 1: In metal carbonyl complexes, synergic back-bonding (d_pi -> pi* of CO) weakens the carbon-oxygen triple bond, reducing the CO bond strength. Step 2: A higher negative charge on the metal center increases electron density, increasing back-donation and weakening the CO bond. A positive charge on the metal decreases back-donation, keeping the CO bond strong. Step 3: Thus, back-donation increases in the order [Mn(CO)6]^+ (weakest back-donation) < [Cr(CO)6] < [V(CO)6]^- (strongest back-donation), meaning CO bond strength increases in the order [V(CO)6]^- < [Cr(CO)6] < [Mn(CO)6]^+, matching option (b).