Charge disproportionation in the organic conductor, alpha-(BEDT-TTF)(2)I-3

We have carried out C-13-NMR measurements on the quasi two-dimensional organic conductor alpha-(BEDT-TTF)(2)I-3, which exhibits metal-insulator transition at 135 K at ambient pressure. The relaxation rate T-1(-1) has two components below the transition. Temperature dependence of the lineshape clearly indicates that there exist two differently charged BEDT-TTF molecules below the transition temperature. (C) 2000 Published by Elsevier Science Ltd.