INTERACTIONS IN CRYSTALS .89. DONOR ACCEP TOR COMPLEXES OF ALKYL AND AMINOBENZENES, ANTHRACENE OR PYRENE AND 1,3,5-CYANO/NITRO-BENZENES - CRYSTALLIZATION, STRUCTURES AND ELECTRONIC-SPECTRA/

The following mixed-stack donor/acceptor complexes {D ... A}(infinity) have been crystallized and their structures determined: {hexamethylbe nzene ... 3,5-dicyano-1-nitrobenzene}(infinity), {hexamethylbenzene .. . 3,5-dinitro-1-cyanobenzene}(infinity), {pyrene ... 3,5-dinitro-1-cya nobenzene}(infinity), {anthracene ...(3,5-dinitro-1-cyanobenzene)(2)}( infinity), {N,N-dimethylanilin ... 3,5-dinitro-1-cyanobenzene}(infinit y) and {1,3-phenylenediamine ... 3,5-dinitro-1-cyanobenzene}(infinity) . Their lattice packing consists of parallel layers, which contain eit her donors adn acceptors as for hexamethylbenzene and pyrene or compos ite ones as in the 1:2 complex of anthracene with each one of the acce ptors above and below its peripheral rings. The isostructural hexameth ylbenzene complexes exhibit almost identical packing coefficients as w ell as a hexagonal coplanar arrangement of the C-6(CH3)(6) donors. Wea k intermolecular van der Waals interactions are also observed between antiparallel cyano substituents. The interplanar pi distances range be tween 334 and 353 pm, i.e. around 340 pm of two van der Waals pi radii . In none of the complexes, however, significant structural changes in either the donor or the acceptor components due to the complex format ion are observed. In both the crystals as well as in solution, the don or/acceptor complexes exhibit colours between yellow and red; their lo ng-wavelength charge transfer absorption maxima, therefore, correspond to a lowering in excitation energy of only up to 1 eV relative to tha t of the components. The different charge transfer in the ground and t he CT excited states is also discussed referring to other data such as vertical first ionization energies of interplanar distances {D ... A} , as well as to results from semiempirical calculations based on the c rystal structure data determined adn including approximate configurati on interaction.