Question

The donation of lone pair of electrons of $CO$ carbon into the vacant orbital of metal atom results in _______.

• A. back bond
• B. $\sigma$- bond
• C. $\pi$-bond
• D. synergic bond

Answer 1

The correct option is B $\sigma$- bond

Synergic bonding interactions are present in metal carbonyls. The sigma bond is formed when lone pair of electrons of carbonyl carbon is donated to vacant orbital of metal. To form a pi bond, an electron pair donated from filled metal d orbital to vacant anti bonding pi orbital of $CO$.
Hence, option (a) is correct.