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New superconducting charge-transfer salts (BEDT-TTF)4[A·M(C2O4)3]·C6H5NO2 (A = H3O or NH4, M = Cr or Fe, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene)

2001; Royal Society of Chemistry; Volume: 11; Issue: 9 Linguagem: Inglês

10.1039/b101134k

1364-5501

Samina Rashid, Scott S. Turner, Peter Day, Judith A. K. Howard, Philippe Guionneau, Eric J. L. McInnes, Frank E. Mabbs, Robin J. H. Clark, Steven Firth, Tim Biggs,

Inorganic Chemistry and Materials

The syntheses, crystal structures, and physical properties of two new crystalline charge-transfer salts of BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, containing tris(oxalato)metallate(III) anions of 3d elements are reported. Electrochemical oxidation of BEDT-TTF in the presence of (NH4)3[Fe(C2O4)3]·3H2O or (NH4)3[Cr(C2O4)3]·3H2O in C6H5NO2, yields crystals of β′′-(BEDT-TTF)4[A·Fe(C2O4)3]·C6H5NO2[1] or β′′-(BEDT-TTF)4[A·Cr(C2O4)3]·C6H5NO2[2] (A = H3O+ or NH4+). The crystal structure of [1] has been solved at 120 K in the monoclinic space group C2/c, and that of [2] in the same space group at 298 and 120 K. For [1], a = 10.273 Å, b = 19.949 Å, c = 35.030 Å, β = 92.97°, V = 7169.6(2) Å3, Z = 8. For [2], at 298 K: a = 10.304 Å, b = 20.091 Å, c = 35.251 Å, β = 92.70°, V = 7289.3(2) Å3, Z = 8, and at 120 K a = 10.283 Å, b = 19.917 Å, c = 34.939 Å, β = 93.30°, V = 7144.4(1) Å3, Z = 8. The crystal structures of both compounds consist of alternating layers of BEDT-TTF cations and layers containing [M(C2O4)3]3−, H3O+ or NH4+, and PhNO2. The BEDT-TTF molecules are arranged in the β′′ packing motif and the tris(oxalato)metallate(III) ions form the well-known honeycomb motif found in many molecular based magnets. SQUID magnetometry, Raman spectroscopy and electron paramagnetic resonance (EPR) measurements were performed on crystals of [1]. SQUID magnetometry, single-crystal four-probe conductivity measurements, Raman spectroscopy, EPR and polarised infrared reflectance were performed on crystals of [2]. Both compounds have metal to superconducting transitions with Tc = 6.2 K for [1] and for [2], Tc = 5.8 K.