Nature and Origin of Stable Metallic State in Organic Charge-Transfer Complexes of Bis(ethylenedioxy)tetrathiafulvalene

The complex formation of bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) with 29 organic electron acceptors and six organic anions yielded 37 charge-transfer (CT) complexes, about three-quarters of which exhibited metallic behavior. The BEDO-TTF molecule proves to be an excellent source for stable metals irrespective of the structure, shape, size, and electron affinity of counter components. The crystal structure of metallic BEDO-TTF complexes indicates a strong aggregation of donor molecules into a two-dimensional (2D) layered structure by the aid of both intermolecular CH···O and side-by-side heteroatom contacts. Band calculations based on an extended Huckel method demonstrate that the sulfur atoms of the BEDO-TTF molecule are dominant for 2D intermolecular overlap. The resulting 2D electronic bands with large band width serve to stabilize the metallic state even at low temperatures. A comparison between the structural properties of complexes of BEDO-TTF and those of its sulfur analog BEDT-TTF (BEDT-TTF...