Multi-layered molecular charge-transfer salts containing alkali metal ions

Abstract

The synthesis, crystal structure and physical properties of two new BEDT-TTF charge-transfer salts containing the tris(oxalato)ferrate(III) anion are described. The most commonly found tris(oxalato)metallate(III) salts of BEDT-TTF contain alternating layers of BEDT-TTF cations and tris(oxalato)metallate anions, but the two salts reported here are multi-layered structures. Compound I is of the type ABCDABCDA as observed previously in the proton-conducting compound β″-(BEDT-TTF)4[Fe(C2O4)3]2·18-crown-6·9HxO and the alpha–beta family of salts α,β″-(BEDT-TTF)4[(NH4)Ga/Fe(C2O4)3]·G (G = PhN(CH3)COH, PhCH2CN and PhCOCH3). In α‴-(BEDT-TTF)9[Fe(C2O4)3]8Na18(H2O)24 (I) the A layers consist of only BEDT-TTF, B/D layers consist of tris(oxalato)ferrate(III) and sodium, and the C layers consist of sodium and water. In α-(BEDT-TTF)10(18-crown-6)6K6[Fe(C2O4)3]4(H2O)24 (II) the packing is of a type not seen before, ABCBABCBA. The A layers in II consist of only BEDT-TTF, B layers consist of tris(oxalato)ferrate(III), potassium, water and 18-crown-6, and C layers consist of 18-crown-6, potassium and water. Both salts are semiconductors between room temperature and 140 K.