The Black Polymorph of TTF-CA: TTF Polymorphism and Solvent Effects in Mechanochemical and Vapor Digestion Syntheses, FT-IR, Crystal Packing, and Electronic Structure

SAUL H. LAPIDUS; AMIT NAIK; ALEX WIXTROM; NESTOR E. MASSA; VINH TA PHUOC,; LEIRE DEL CAMPO; SEBESTIEN LEBEGUE,; JAYNOS G. AYGYAYN,; TAREK ABDEL-FATTAH,; SILVINA PAGOLA

CRYSTAL GROWTH & DESIGN

AMER CHEMICAL SOC

Lugar: Washington; Año: 2014 vol. 14 p. 91 - 100

1528-7483

Tetrathiafulvalene-chloranil (TTF-CA) was synthesized by two methods, liquid assisted grinding (LAG) and vapor digestion(VD), which largely reduce the use of reaction solvents. The effects ofthe small quantities of LAG solvent and solvent vapors in VD towardthe formation of a particular TTF-CA product polymorph were studied from both tetrathiafulvalene forms (orange and brown) as reactants. It was concluded that a high solvent polarity index favors the formation of the ionic black polymorph of TTF-CA vs the quasineutral green form, whereas the crystal structure and crystal habit of the orange tetrathiafulvalene polymorph also favors the formation ofthe black TTF-CA. The crystal structure of the black TTF-CA was determined from synchrotron X-ray powder diffraction (XRPD), and it consists of dimerized TTF+? and CA−? radical ions, in agreement with room temperature magnetic susceptibility measurements indicating the material is diamagnetic. FT-IR showed that the compound is a semiconductor with a small band gap of ∼0.198 eV and it remains ionic at low temperatures. The latter was confirmed by XRPD showing the black TTF-CA does not undergo a phase transition in the range 298−20 K. Band structure calculations are in good agreement with the measured band gap.