Superconducting and Semiconducting Magnetic Charge Transfer Salts: (BEDT-TTF)4AFe(C2O4)3.cntdot.C6H5CN (A = H2O, K, NH4)

Abstract

We have shown that the hexagonal layer motif [AM{sup III}(C{sub 2} O{sub 4}){sub 3}]{sup n-} containing bridging oxalate groups, which has been shown to form a wide variety of compounds with electronically inactive counter-cations having unusual cooperative magnetic properties, can also stabilize lattices containing the organic {pi}-donor BEDT-TTF. In the compounds whose structures we describe here, (BEDT-TTF){sub 4}AFe(C{sub 2}O{sub 4}){sub 3}.C{sub 6}H{sub 5} CN (A = H{sub 2}O, K, NH{sub 4}), the lattice is stabilized by C{sub 6} H{sub 5}CN molecules included in the hexagonal cavities. The packing of the BEDT-TTF in the A = K, NH{sub 4} phases is of a type not previously observed with spin-paired (BEDT-TTF){sub 2}{sup 2+} separated by closed shell (BEDT-TTF){sup 0}, while that in the superconductor is of {Beta}{double_prime} type. Both the superconducting A = H{sub 2}O and semiconducting A = K, NH{sub 4} phases contain high spin 3d{sup 5} Fe{sup III} with only very weak exchange interaction between them. Additional low temperature and high magnetic field experiments (e.g., of Schubnikov-de Haas oscillatory magnetoresistance) will be needed to delineate the Fermi surface in the superconductor. 36 refs., 11 figs., 4 tabs.