Three-Dimensionally-Modified Tetracyanoquinodimethanes and Their Charge-Transfer Complexes with Tetrathiafulvalene Derivatives Having a Wide Range of Ionicity

Eight different 1:1 charge-transfer(CT) complexes were prepared using tetrahydrobarreleno-tetracyanoquinodimethane(THBTCNQ), dihydrobarreleno-tetracyanoquinodimethane(DHBTCNQ), monobenzobarreleno-tetracyanoquinodimethane(MBBTCNQ), and dibenzobarreleno-tetracyanoquinodimethane(DBBTCNQ) as tetracyanoquinodimethane(TCNQ)-type acceptors, and tetrathiafulvalene(TTF), bis(tetramethyene)-tetrathiafulvalene(OMTTF), and tetramethyl-tetrathiafulvalene(TMTTF) as TTF-type donors. The complexes can be classified into three distinct groups, I–III, on the basis of the magnitude of both the degree of CT and the electrical resistivity of compacted powders. Group-I complexes are characterized by a small band gap semiconductivity and moderate CT, group-II complexes by low conductivity and small CT, and group III complexes by low conductivity and complete CT. The stacking mode of the three groups of complexes are discussed, by comparing the electronic absorption spectra of the three groups of CT complexes with those of the complexes for which the crystal structures are known. A crystal structure analysis of OMTTF–DBBTCNQ revealed that it is the first example of a highly ionic CT complex of a TTF–TCNQ type with a regular mixed stacking mode. These three groups of complexes containing bulky acceptor groups will be of theoretical interest in studying the crystal properties of organic CT complexes.