beta(CO)-(ET)(2)I-3: Co-existence of ordered beta-(ET)(2)I-3 (T-c approximate to 8 K) and disordered beta-(ET)(2)I-3 (T-c approximate to 2 K)

The crystal structures of beta (CO)-(ET)(2)I-3 were determined at temperatu res of 293, 200, 130, 100, and 35 K from X-ray single crystal diffraction d ata. At 293 K, one ethylene group of the ET cations is disordered with the eclipsed conformation prevailing over the staggered conformer; at 200 K the occupancies of both arrangements are equal. Upon cooling to 130 K and belo w, about 60 % of the ethylene groups adopt a staggered conformation, thus p roviding evidence for a temperature-induced, partial ordering process.