Band structures of organometallic polymers containing mu(2)-bridging pentalene or indacene as ligands for transition metals (Fe, Co, Ni) have been calculated by using the tight-binding crystal orbital method. These organometallic polymers are an infinite model of bimetallic complexes of pentalene or s-indacene with pentamethylcyclopentadiene. Polymers containing pentalene and s-indacene with iron atoms possess small band gaps with broad bands near the Fermi level. On the other hand, polymers containing cobalt or nickel atoms exhibit a metallic or semi-metallic character, which suggests the possibility of changes in their structures. We have analysed the crystal orbital phases to examine the electronic structures. (C) 2008 Elsevier B.V. All rights reserved.