I. INTRODUCTION One-dimensional organometallic sandwich polymers (OSPs) have attracted wide inter- ests in recent years due to their potential applications in spintronic devices and information storage [1–16]. One of the extensively studied systems is TM$_{n}$Bz$_{n}$ +1 which demonstrates versatile properties. The property diversity arises from two facts. On one hand, the prop- erties of [TM(Bz)] ∞ are highly dependent on the TM ions. For example, [V(Bz)] ∞ and [Mn(Bz)] ∞ are ferromagnetic half-metals, while [Cr(Bz)] ∞ is a nonmagnetic insulator. On the other hand, the type of organic molecules can also significantly influence the properties of the one-dimensional OSPs. For example, no magnetic moment appears in [Mn(Cp)] ∞ (Cp = cyclopentadienyl), while [Cr(Cp)] ∞ has a ferromagnetic ground state.[10–12] It is believed that the ferromagnetism obsvered in such OSPs (like V$_{n}$Bz$_{n}$ +1 [1]) may qualify them as good materials for spin polarized transport.[4–7] Because of the abundant magnetic properties and the possibility as candidates for spin- tronic devices and information storage, recently, the study on the one-dimensional OSPs has been extended to the cases of TM-pentalene (Pn), TM-naphthalene (Np) and TM-Ant.[13– 16] The sandwich like clusters of TM-Np and TM-Ant were firstly synthesized in 1999.[13] Further theoretical investigations showed that [V 2 (Ant)] ∞ is a half-metallic ferromagnet. Since in [TM 2 (Ant)] ∞ , the Ant are connected by two TM ions, as shown in Fig 1(a), com- pared with [TM(Bz)] ∞ and [TM(Cp)] ∞ , it should have better stability and conductivity and it may be more suitable for spintronic devices and information storage. Note that, previous theoretical investigation pointed out a possible structural transition from D$_{6}$$_{h}$ to D$_{2}$ symme- try appearing on V$_{n}$Bz$_{n}$ +1 .[4] Consequently, systematic investigate on this kind of polymers is quite interesting and necessary. Therefore, in this work, the structural, electronic and magnetic properties of [TM 2 (Ant)] ∞ (TM=Sc, Ti, V, Cr and Mn) are investigated by first principles calculations. We find that magnetic properties in [TM 2 (Ant)] ∞ are much dif- ferent from those in TM(Bz) ∞ and the difference arises from the different HOMO-LUMO gap of the organic molecules and the subsquent different CT between the TMs and the or- ganic molecules. Especially, we find that [V 2 (Ant)] ∞ and [Cr 2 (Ant)] ∞ are half metals with the 100% spin polarized density of states (DOS) around the Fermi level, which is of great importance for spin transport. 2