HYDROGEN-BOND TUNING OF MACROSCOPIC TRANSPORT-PROPERTIES FROM THE NEUTRAL MOLECULAR-COMPONENT SITE ALONG THE SERIES OF METALLIC ORGANIC-INORGANIC SOLVATES (BEDT-TTF)4RE6SE5CL9.[GUEST], [GUEST = DMF, THF, DIOXANE]

A series of single crystals of tetrakis[3,4,3',4'-bis(ethylenedithio)-2,2',5,5'-tetrathiafulvalene]Re6Se5Cl9.-[guest] (2a-d) have been prepared where the monoanion is a hexanuclear chalcohalide rhenium cluster and the neutral guest molecules are dimethylformamide (DMF) in 2a (monoclinic modification) and 2b (triclinic modification), tetrahydrofuran (THF) in 2c, and dioxane in 2d. All four compounds present the same basic structural organization in which conducting organic cation radical slabs are sandwiched by inorganic cluster monoanion layers. The guest molecules are shown to be selectively incorporated into a single site located at the organic-inorganic interface of these layer-like structures. In compounds 2c and 2d, a set of C-H...O hydrogen bonds is found to anchor the THF and dioxane molecules to the organic slabs. Although the four compounds are metallic at room temperature, their electrical conductivity at low temperatures and their degrees of structural ordering are shown to strongly depend upon the size, shape, and symmetry of the neutral guest molecule. The latter induces structural changes which are shown to be associated with significant modifications of the band electronic structures, Fermi surfaces, and ultimately the dimensionality of the materials. Altogether, the activated conductivity behavior observed from 90 K down to low temperatures in the case of the disordered DMF solvates 2a and 2b appears at only 50 K in the THF-phase 2c. The inclusion of dioxane successfully orders the structure in 2d, and the metallic regime is then found to be sustained down to 4.5 K.