ORIGINAL PAPER Layered, Two-Dimensional Hydrogen Bonding Nets in the Structure of the 1:1 Encounter Complex TMTTF–TCNB: Combined Structural and Spectroscopic Study Eric W. Reinheimer • Maria Fernandez Ballesteros Rivas • Hanhua Zhao • Kim R. Dunbar Received: 28 December 2010 / Accepted: 1 February 2011 / Published online: 19 February 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The synthesis, crystal structure and spectro- scopic properties as determined by infrared spectroscopy of the 1:1 encounter complex TMTTF–TCNB are reported. The complex crystallizes with each of the constituent molecules on an inversion center in the triclinic space group P - 1 with a = 6.7953(16) A ˚ , b = 7.9141(16) A ˚ , c = 9.775(2) A ˚ , a = 98.63(3)°, b = 105.27(3)°, and c = 94.49(3)°. The determination of this crystal structure provided cyanide bond distances which when compared to the reported literature values for free TCNB suggest the presence of the neutral acceptor. The central C=C bond and four ancillary C–S bonds in TMTTF provide structural evidence that the donor, like the acceptor, also exists in its neutral state. These crystallographic observations and conclusions were confirmed by infrared spectroscopic analysis. Of particular interest is a two dimensional hydrogen bonding net which occurs within the (13  1) plane. When stacked as repeat units along the a axis, this net is reminiscent of stacked graphene layers in graphite. Keywords TMTTF Á Tetracyanobenzene Á TTF Introduction The field of organic materials that display charge transfer properties has been a research topic of considerable interest since the discovery of metallic conductivity in the charge transfer salt TTF–TCNQ. In this material, partial chemical oxidation of tetrathiafulvalene (TTF) by TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) results in the formation of a charge transfer salt with metallic conductivity that reaches a maximum of 10 4 S cm -1 at 66 K prior to under- going a metal-to-insulator transition [1–3]. Concomitant with the partial charge transfer is the solid state organization of the donor and acceptor molecules into segregated stacks. This packing orientation maximizes molecular orbital overlap among molecules of similar symmetry thus creating a more facile pathway for the transfer of itinerant electron density. Although the purely organic material TTF–TCNQ is considered a seminal discovery in the realm of TTF-based complexes, a considerably larger number of charge transfer salts have been prepared electrochemically via slow galva- nostatic oxidation at the surface of platinum electrodes in the presence of inorganic anions of various charges and geometries [4]. Central to this field of research is the prep- aration of multifunctional hybrid materials exhibiting physical properties once considered inimical in a continuous crystalline lattice [5–14]. Various novel materials have also been obtained using substituted TTF derivatives. Among those derivatives is the permethylated-TTF 2,3,6,7-tetramethyl-1,4,5,8-tetra- thiafulvalene (TMTTF) which has seen widespread use throughout the field of organic materials. For example, salts have been prepared electrochemically between TMTTF and E. W. Reinheimer (&) Á M. F. B. Rivas Á H. Zhao Á K. R. Dunbar Department of Chemistry, Texas A&M University, College Station, TX 77842-3012, USA e-mail: ewreinheimer@csupomona.edu Present Address: E. W. Reinheimer Department of Chemistry, California State Polytechnic University, 3801 W. Temple Ave., Pomona, CA 91768, USA Present Address: M. F. B. Rivas Departmento de Quı ´mica, Universidad Nacional Auto ´noma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510 Coyoacan, DF, Mexico 123 J Chem Crystallogr (2011) 41:936–943 DOI 10.1007/s10870-011-0021-y