Question

Which of the following has the smallest bond order for CO? [Mn(CO)6]+, Cr(CO)6, [Ti(CO)6]2−, [V(CO)6]−

Answer 1

Answer:

Explanation:

The Ti^2 −

complex, involving the most negative oxidation state out of all these  

d ^6 complexes (Ti ^2−   being the most electron-rich metal center), is actually the one with the smallest bond order within the   C−O bond because it will involve the most  π  back-bonding.

The more  π backbonding into the  π *  of  CO , the more weakened the  C − O

bond is, within itself.

CARBONYL LIGANDS ARE BOTH SIGMA DONORS AND PI ACCEPTORS

One of the most easily forgotten concepts here to remember is that  

CO  is a  σ  donor AND  π  acceptor, since it has both a  σ  HOMO and two  

π *  LUMOs.