The preparation of multiple-decker sandwich clusters V-n(C6H6)(n+l) and their large size dependence of the ionization energies have recently been reported by Kaya and his co-workers (J. Phys. Chem. 1995, 99, 3053). In the present paper, the bonding scheme between benzene and metal atoms (Ti, V, and Cr) was investigated by using Mayer's bond order analysis with ab initio MO calculations, and it was attributed mainly to the delocalization of metal d delta electrons via the LUMOs of the benzene molecules. Moreover, the lowest ionization of most multiple-decker sandwich clusters was found to occur from the upper end of the d delta orbitals, and the large size dependence of the ionization energies was also related to the significant one-dimensional delocalization of these d delta electrons. The proposed Huckel type treatment for these frontier orbitals explains the above properties very simply and suggests also the large size dependence of the photoabsorption band positions and even the thermodynamical stability of the one-dimensional polymer materials denoted by [M(C6H6)](infinity) Besides, the ionization energies of these polymeric species are estimated to be 2.68, 3.15, and 4.28 eV for M = Ti, V, and Cr, respectively.