CONFORMATIONAL POLYMORPHISM OF OLIGOTHIOPHENES - X-RAY STRUCTURE OF THE MONOCLINIC FORM OF 3,3',4'',3'''-TETRAKIS(METHYLSULFANYL)-2,2' 5',2''/5'',2'''-QUATERTHIOPHENE/

Conformational polymorphism of an oligothiophene, the title compound ( T4S), is reported for the first time. Efficient synthesis of T4S produ ced, in addition to the triclinic, deep orange crystals reported previ ously, a second (yellow monoclinic) form of T4S. whose structure as re vealed by single-crystal X-ray diffraction is presented here. The synt hetic pathway is outlined and the molecular structure and crystal pack ing are dis cussed. The significantly different pi-delocalization in t he two conformations indicates the need for very careful molecular cha racterization.