Tin(IV) sulfide alkylamine composite mesophase: a new class of thermotropic liquid crystals

The synthesis, structural characterization, thermal, electronic, optical birefringence and electrical properties of a new class of semiconducting 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 sandwiched well organized hexadecylamine bilayers. On warming this material to around 45 degrees C the hexadecylamine bilayer first becomes disordered while the porous tin(Iv) sulfide sheets remain registered. This is followed, around 85 degrees C, by a transition where both the alkylamine bilayer and the porous tin(Iv) sulfide lamellae become liquid crystalline at which point the intralayer but not the interlayer registry is lost. The liquid-crystal organic-inorganic composite phase has either a nematic or smectic C structure. Electrically, the room-temperature ordered phase has a conductivity of 5.3 x 10(-8) Omega(-1) cm(-1) which increases by more than a 1000 times on transforming to the LC phase where it behaves as a semiconducting metallogen. The conductivity of Meso-SnS-1 cycles reversibly with temperature and displays discontinuities that are coincident with the crystal-semiliquid crystal and semiliquid crystal-liquid crystal thermal transitions that are defined by differential scanning calorimetry and variable-temperature powder X-ray diffraction. Meso-SnS-1 readily forms electrically conducting thin films which are able to reversibly adsorb molecules like H2O and CO2. These properties bode well for the use of this new class of inorganic semiconducting LCs for electro-optical displays and chemical sensing applications.