Binuclear Cp2M2(mu-C8H8) derivatives have been synthesized for M = V, Cr, Co, and Ni and have now been studied theoretically for the entire first row of transition metals from Ti to Ni. The early transition metal derivatives Cp2M2(mu-C8H8) (M = Ti, V, Cr. Mn) are predicted to form low-energy cis-Cp2M2(mu-C8H8) structures with a folded C8H8 ring (dihedral angle similar to 130 degrees) and short metal-metal distances suggesting multiple bonding. These predicted structures are close to the experimental structures for M = V, Cr with V V and Cr Cr bond lengths of similar to 2.48 and similar to 2.36 angstrom, respectively. The middle to late transition metals form trans-Cp2M2(mu-C8H8) structures (M = Mn, Fe, Co, Ni) with a twisted mu-C8H8 ring and no metal-metal bonding. The hapticity of the central mu-C8H8 ring in such structures ranges from five for Mn and Fe to four for Co and three for Ni and thus depend on the electronic requirements of the central metal atom. This leads to the favored 18-electron configuration for both metal atoms in the singlet Fe, Co, and Ni structures but only 17-electron metal configurations in the triplet Mn structure. In addition, the late transition metals form trans-Cp2M2(mu-C8H8) structures (M = Fe, Co, Ni), with the tub conformation of the mu-C8H8 ring functioning as a tetrahapto (M = Fe, Co) or trihapto (M = Ni) ligand to each CpM group. A mu-C8H8 ring in the tub conformation also bonds to two CpFe units as a bis(tetrahapto) ligand in both singlet and triplet cis-Cp2Fe2(mu-C8H8) structures.