Organic Metals from Chiral BEDT-TTF Donors

Abstract

The chemistry and physics of solids with layered structures has been of central interest in the solid state sciences for several decades I I]. One of the many scientifically and technically imponant aspects connected with these materials is the possibility of pronounced two-dimensional delocalized interatomic and/or intennolecular electronic interactions, which lead to unusual magnetic and electric properties in the bulk. Especially remarkable are a variety of phase transitions. which occur in selected materials of this type at different temperatures.Typical, and very welJ -known. examples of such specimens are graphite, the binary sulfides MoS 1 and TaS2' together with several of their intercalation compounds, ternary or quarternary chalcogenides and/or halides of the transition elements, and so on. Inorganic ternary systems. composed of anionic bansition metal oxide layers and different kinds of countercarions located between these anion sheets. are especially well-suited for systematic variations in composition and -as a consequence thereof -in solid state properties. Varying stages of band fillings can be achieved "chemically," depending on the number of electrons per metal ion in the different sheets. The systematic work on these materials culminated in the discovery of superconductivity above 40 K by MiiUer and Bednorz in layered copper oxide structures (2).With the exception of graphite-related compounds -which consist mainly of carbon-there were no comparable classes of electronically collective interacting layered organic materials. Most of the two-dimensional organic solids -which means layered matrices made up mainly of !he main group elements carbon, nitrogen, oxygen, hydrogen and sulfur -are diamagnetic and Insulating. The electrically conducting andlor magnetically interesting organic charge transfer solids, on the other hand, contain columns or chains of interacting molecules or atoms. Th is arrangemem results in pronounced "o ne-dimen sio nal" physical properties, with the well-known phase transi tions at comparatively high temperatures. STATUS QUOUp to now, there is one organic two-dimensional "exception:" the cation radical salts of the donor BEDT-TIF. Numerous BEDT-TTF salts -metallic, semiconducting and/or insulating -have been prepared in the last few years [3,4]