Charge ordering in the TMTTF family of molecular conductors

Using one- and two-dimensional NMR spectroscopy applied to C-13 spin-labele d (TMTTF)(2)AsF6 and (TMTTF)(2)PF6, we demonstrate the existence of an inte rmediate charge-ordered phase in the TMTTF family of charge-transfer salts. At ambient temperature, the spectra are characteristic of nuclei in equiva lent molecules. Below a continuous charge-ordering transition temperature T -co, there is evidence for two inequivalent molecules with unequal electron densities. The absence of an associated magnetic anomaly indicates only th e charge degrees of freedom are involved and the lack of evidence for a str uctural anomaly suggests that charge-lattice coupling is too weak to drive the transition.