The correct electronic configuration of frontier MO’s of  Mn(η5−C5Me5)2\text{Mn}(\eta^5-\text{C}_5\text{Me}_5)

Correct option is A

The cyclopentadienyl metallocenes of the elements of transition metals of 3d series are isomorphous. Except ferrocene, all other metallocenes are paramagnetic.

The molecular orbital energy diagram supported by photoelectron spectroscopy studies in conjunction with ligand field theory for ferrocene in figure.

The energy of a_1gorbital of cyclopentadiene is too much less than a_1g(4s or 3dz² ) orbitals, therefore, a_1gorbital of the ring interacts slightly with a_1gorbitals of iron. Thus, a_1gbonding molecular orbital is mainly ligand based and a_1g(3dz²) orbital is non-bonding and localized on the metal. Similarly, the a_2uorbital has little interaction with even higher energy Fe 4p_zorbital with which it is formally able to combine. The pair of e_1gMOs arises from the bonding combination of the ligand e_1gorbitals with e_1g(dxz and dyz) orbitals on metal and form two strong pi-bonds. This is due to the reason that energy difference between e_1gorbitals of ligand and e_1gorbitals of metal and their symmetries are well-matched. This is the main contribution to the stability of the complex. The corresponding anti-bonding e_1g^*orbitals are unoccupied but involve in electronic transitions. Although the interaction of ligand e_1uorbitals with metal e_1u(px, py) orbitals is favourable, but due to large energy difference they interact very little and the e_1umolecular orbitals are again mainly ligand based but with some contribution from metal 4p_xand 4p_yorbitals. Since the energy of ligand e_2gorbitals is higher than those of e_2g(dxy and dx²-y²) orbitals of same symmetry of the metal, they do not interact very effectively and, therefore, the e_2gmolecular orbitals are metal based and are non-bonding. Also the metal a_1g(i.e., dz²) orbital does not interact very effectively with a_1gorbitals of the ligand, therefore, is localized on metal and is non-bonding.

The orbitals of metallocenes that are of most interested are those having the greatest d-orbital character. These orbitals are the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO respectively).

The electron-electron repulsion between the pi-electron density of the ligand e_2gorbitals and the metal e_2g(dx²-y²and dxy) orbitals is minimum as the lobes of the dx²-y²and dxy orbitals are not directed towards the cyclopentadiene ring. The a_1g(dz²) orbital has one lobe and e_1g(dyz and dzx) orbitals have two lobes directed towards the cyclopentadiene ring and, therefore, repulsion between a_1gof metal and that of Cp ring lower than between e_1gof metal and e_1gof Cp ring.