TIN(IV) SULFIDE ALKYLAMINE COMPOSITE MESOPHASE - A NEW CLASS OF THERMOTROPIC LIQUID-CRYSTALS

The synthesis, structural characterization, thermal, electronic, optic al birefringence and electrical properties of a new class of semicondu cting tin sulfide based thermotropic liquid crystals (LCs), Meso-SnS-n , are described for the first time. The assynthesized crystalline form of Meso-SnS-1 has a structure that is based upon well registered yet poorly ordered porous tin(Iv) sulfide layers between which are sandwic hed well organized hexadecylamine bilayers. On warming this material t o around 45 degrees C the hexadecylamine bilayer first becomes disorde red while the porous tin(Iv) sulfide sheets remain registered. This is followed, around 85 degrees C, by a transition where both the alkylam ine bilayer and the porous tin(Iv) sulfide lamellae become liquid crys talline at which point the intralayer but not the interlayer registry is lost. The liquid-crystal organic-inorganic composite phase has eith er a nematic or smectic C structure. Electrically, the room-temperatur e ordered phase has a conductivity of 5.3 x 10(-8) Omega(-1) cm(-1) wh ich increases by more than a 1000 times on transforming to the LC phas e where it behaves as a semiconducting metallogen. The conductivity of Meso-SnS-1 cycles reversibly with temperature and displays discontinu ities that are coincident with the crystal-semiliquid crystal and semi liquid crystal-liquid crystal thermal transitions that are defined by differential scanning calorimetry and variable-temperature powder X-ra y diffraction. Meso-SnS-1 readily forms electrically conducting thin f ilms which are able to reversibly adsorb molecules like H2O and CO2. T hese properties bode well for the use of this new class of inorganic s emiconducting LCs for electro-optical displays and chemical sensing ap plications.