| Summary: | More than one hundred and twenty conducting salts based on the organic donor-molecule BEDT-TTF are known, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene (abbreviated herein as ET). Several of the early salts possessed tetrahedral and octahedral anions, such as (ET){sub 2}ClO{sub 4}(TCE), (ET){sub 2}PF{sub 6}, (ET){sub 2}ReO{sub 4}, and (ET){sub 2}BrO{sub 4}. The perchlorate salt is metallic to 1.4 K,{sup 1} and the perrenate derivative was the first ET based organic superconductor ({Tc} 2 K, 4.5 kbar). Since the discovery of ambient pressure superconductivity in {beta}-(ET){sub 2}I{sub 3} ({Tc} 1.4 K),{sup 5} other isostructural {beta}-(ET){sub 2}X salts have been prepared with higher {Tc}'s. A structure-property correlation for the {beta}-type salts has been reviewed in this volume; it predicts that {Tc}'s higher than 8K are possible if {beta}-salts with linear anions longer than I{sub 3}{sup {minus}} can be synthesized. During the search for new linear anions, a variety of compounds with discovered with polymeric anions. The report of superconductivity in {kappa}-(ET){sub 4}Hg{sub 3}X{sub 8} (X = Cl, {Tc} 5.4 K 29 kbar and X = Br, {Tc} 4.3 K ambient pressure and 6.7 K 3.5 kbar) and {kappa}-(ET){sub 2}Cu(NCS){sub 2} ({Tc} 10.4 K) further stimulated the search for novel polymeric anions. A general synthetic strategy for preparing new salts containing polymeric anions is to couple a coordinatively unsaturated neutral transition metal halide/pseudohalide with a simple halide or pseudohalide during an electrocrystallization synthesis. In this article, the authors discuss three new ambient pressure organic superconductors with novel polymeric anions, {alpha}-(ET){sub 2}(NH{sub 4})Hg(SCN){sub 4}, {beta}m-(BO){sub 3}Cu{sub 2}(NCS){sub 3} and {kappa}-(ET){sub 2}Cu(N(CN){sub 2})Br. 48 refs., 8 figs., 2 tabs.
|
|---|