What kind of molecular orbitals are formed when d-orbitals overlap?
When you deal with the MO treatment of transition metal complexes (the only way to go) such as in [Co(NH3)6]^3+ you do not hybridize the TM AOs but rather overlap the TM AOs separated according to symmetry with linear combinations of ligand σ orbitals (:NH3 lone pairs). For example, the 3dx^2-y^2 Cr AO (part of the Eg set) is overlapped with the four NH3 σ orbitals in the x/y plane using the appropriate phase sign (ψ(Eg) = [3d(x^2-y^2) + σx, +σy, -σ-x, -σ-y). But I don’t think this is what you you are looking for. The only time you get a bonding overlap of two d orbitals on two atoms is when you have quadruple bonds between two transition metals as in [Re2Cl8]2- and [Cr2(OAc]4 [1]. The bonding consists of a σ bond, two π bonds, and a δ bond. The last bond is produced by the four fold overlap of the two 3dxy AOs on each TM (z is the MM axis). Take your thumb and three fingers on each hand and bring them together: this is the overlap. It results in a large 3dxy-type MO situated between t
