Electronic and Magnetic Properties of Metal-(4,4′-bipyridine) Sandwich Complexes and Their Nanowires

Using calculations based on density functional theory, we have investigated the geometric, energetic, and magnetic properties of complexes of 4,4'-bipyridine (BPY) with metal atoms M (= Li, V, and Ti). The systems of interest include BPY-M-2 and BPY2-M-2 complexes and (BPY-M-2)(x) nanowires in which the sandwich structure is stacked infinitely along one direction. For each of these systems, a detailed analysis was performed on the electronic structure. First, we found that BPY-M (M = V and Ti) binding is stronger than BPY-Li binding because of the covalent nature of the former interaction. The difference in the magnetic properties of BPY-M-2 and BPY2-M-2 (M = V and Ti) complexes can be understood in terms of the different strengths of the M-M interactions mediated by d(M) or sd(M)-hybridized orbitals. Second, we found that the (BPY-Li-2)(x) nanowire is a semiconductor, whereas (BPY-V-2)(x) and (BPY-Ti-2)(x) nanowires are magnetic metals due to the spin-polarization in d(z)2(M)-derived bands.