Electric dipole of metal–benzene sandwiches

We measured the permanent electric dipole moment of transition metal–(C6H6)2 sandwich complexes in the gas phase. The electric dipole for complexes with Sc, Ti, V, Nb, Ta, and Zr is zero (μ<0.2 D), which is in agreement with a symmetric structure. The electric dipole on the A principal inertial axis of the molecule is 0.7 ± 0.3 D for Co–(C6H6)2, and 1.3 ± 0.3 D for Ni–(C6H6)2. This shows that they have an asymmetric structure.