ONE-DIMENSIONAL STAIRCASE AGGREGATES IN CRYSTALS OF 1,7-BIS(DIMETHYLAMINO)HEPTAMETHINIUM HEXAFLUOROPHOSPHATE, A POLYMETHINE DYE

The title compound C11H19N2 . PF6 crystallises in the monoclinic space group C2/m (no. 12) with a = 1234.4 pm, b = 942.8 pm, c = 717.6 pm, b eta = 109.95 degrees, Z = 2 and D-x = 1.372 g cm(-3). R = 0.08 for 627 unique reflections with I > 2 sigma(I) at 298 K. The cation as well a s the anion are disordered. A polarization of the polymethine system b y the counterion is not observed, be cause the dye molecule exhibits a symmetrical polymethine structure. The chromophores are closely stack ed in one-dimensional staircase aggregates which are separated by the counterions. Their parallel arrangement in the unit cell should lead t o only one transition dipole moment.