Bonding Multiplicity and Internal Rotation

Before proceeding to the discussion of multiple metal-metal bonding it is convenient to analyze briefly the relationship existing between bond order and internal molecular rotation. 

The rotation about a (x-bond is free because the atomic orbital overlapping originating this molecular bond does not change with rotation around the bond axis. In the case of species such as ethylene, where beside the a-bond there is a n one, any rotation about the molecular axis will induce a diminution in the 

In a triple bond with an electron configuration the set of molecular orbitals has a cylindrical symmetry again so the system can rotate internally in a free way. 

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