EPR study of (BEDT-TTF) salts with the magnetic cluster [PMo/sub 12/O/sub 40/]/sup -4/ and the non-magnetic [SiW/sub 12/O/sub 40/]/sup -4/

Summary form only given. We present an EPR study of the conductors, (BEDT-TTF)/sub n/X. Solvate, where n=6 or 8, X=PMo/sub 12/O/sub 40/; n=8, X=SiMo/sub 12/O/sub 40/ and the solvent is a mixture of H/sub 2/O and CH/sub 3/CN. The n=6 salt is metallic and shows two EPR signals (the conduction electrons and those localised on the clusters) while the n=8 salts are semiconductors with a single EPR line average between the free electron g-value and that of the cluster for the Mo and only one signal from the BEDT-TTF for the non-magnetic SiMo/sub 12/O/sub 40/ salt. The line shape of the latter is temperature-dependent; below 125K a second signal grows in intensity at the expense of the first on reducing temperature. The intensities are fitted to a two site model below 125K; the temperature at which a change in the E/sub A/ is observed. This is interpreted as the point where the cluster electron becomes localised on one of the Mo sites. For the n=6 salt the intensities of both signals increase as T is lowered. The results so far indicate that in the two cases with the Mo cluster there is moderate interaction between the conduction electrons and those localised on the clusters.