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Abstract:
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Electronic structure aspects related to the semiconducting properties of monomers and polymers of phythalocyanoiron with bidentate bridging ligands, PcFe-L-2 and -[PcFe(L)](n), have been investigated from density functional calculations [L pyrazine, triazine, tetrazine, pyridine, 4,4 ' -bipyridine, bipyridyacetylene, and bis(4-pyridyl)bencene]. The following relevant results have been obtained: (a) an energy analysis in terms of electrostatic interaction, Pauli repulsion, and occupied/virtual orbital interactions show that the Pauli repulsion is the origin that the axial ligands (L) prefer be located toward the aza positions of the macrocycle, and (b) the intrinsic semiconducting properties depend of the frontier band. The valence band is composed largely by the transition metal d(xy) orbital. The conduction band is composed of a mixture between the metallomacrocycle and bridged ligand orbitals for systems formed by pyrazine, bipyridine, and bipyridyacetylene. However, this composition is different when the ligands are triazine and tetrazine, which show a band composed of pi* orbitals. These systems are predicted to show the higher conductivity within the series, in agreement with experimental results. |