Ab initio Hartree-Fock crystal orbital studies on charge-transfer complexes: Different crystal modifications of the same compounds

Ab initio Hartree-Fock crystal-orbital calculations of dimorph tetramethyltetraselenafulvalene-tetracyanoquinodimethane (TMTSF-TCNQ) and dibenzotetrathiafulvalene-tetracyanoquinodimethane (DBTTF-TCNQ), both as red and black crystals, were carried out. The crystal structures of the red and black TMTSF-TCNQ are essentially different from each other, whereas the red and black DBTTF-TCNQ are qualitatively very similar (although not completely isomorphous). The results of the present calculations definitely show that even subtle differences in the crystal structures are crucial for the electronic properties of the systems under study. (C) 1998 John Wiley & Sons, Inc.