NEET2016ChemistryCoordination CompoundsActual
Which of the following has the longest C − O bond length? (Free C − O bond length in CO is 1 . 128   A o ).
Options
- AN i C O 4
- BCo CO 4 −
- CF e C O 4 2 -
- DMn CO 6 +
Correct answer
C. F e C O 4 2 -
Step-by-step solution
Metal carbon bond in metal carbonyls possess both σ and π character. M − C π bond is formed by donation of a pair of electrons from filled orbital of metal into vacant antibonding π orbital of CO . CO bond length increases if M has more tendency to donate lone pair. Tendency to donate lone pair is Fe 2 − > Co − > Ni > Mn +