Synthesis and Properties of a New Kind of One-Dimensional Conductors. 2. Extended Hückel Calculations on the Energy Band Structure

Abstract

Abstract The co-ordination polymer of tetrazaporphin (TAP) with a transition metal, say FeII , in its center and acetylide anion, C2 2⊖ , as an axial bidentate bridging ligand is taken as a model sub-stance for the new type of one-dimensional conductors introduced in the preceding communication of this series. Although the monomer shows D4h symmetry, this is reduced to C4v for arbitrary kz -values of the Bloch functions of the first Brillouin zone. From the irreducible representations a1, a2, b1, b2, and e only a1 and e have contributions from all components, namely TAP2⊖ , Fe2⊕ and C2 2⊖, so that for these races broad energy bands can be expected. The a2, b1, and b2 MOs of the TAP-FeII subunits are separated fairly well and have no counterparts in the C2 2⊖ bridges so that very narrow bands should arise. This is confirmed by an EH calculation. Unexpectedly the a1 bonds which have contributions from the σ-MOS of C2 2⊖ are broader than the e-bands which contain the two crossed π-MO systems of C2 2⊖ . The quantitative results of the nearly self-consistent iterative EH calculation indicate overlap of the energy bands near the Fermi level and fulfill thus one necessary condition for metal-like electrical conductivity.