Hybrid molecular materials based upon organic pi-electron donors and metal complexes. Radical salts of bis(ethylenethia)tetrathiafulvalene (BET-TTF) with the octahedral anions hexacyanoferrate(III) and nitroprusside. The first kappa phase in the BET-TTF family.

Abstract

The synthesis, structure, and physical characterization of two new radical salts formed with the organic donor bis(ethylenethia)tetrathiafulvalene (BET-TTF) and the octahedral anions hexacyanoferrate(III), [Fe(CN)(6)](3-), and nitroprusside, [Fe(CN)(5)NO](2-), are reported. These salts are (BET-TTF)(4)(NEt(4))(2)[Fe(CN)(6)] (1) (monoclinic space group C2/c with a = 38.867(7) A, b = 8.438(8) A, c = 11.239(6) A, beta = 90.994(9) degrees, V = 3685(4) A(3), Z = 4) and (BET-TTF)(2)[Fe(CN)(5)NO].CH(2)Cl(2) (2) (monoclinic space group C2/c with a = 16.237(6) A, b = 18.097(8) A, c = 12.663(7) A, beta = 106.016(9) degrees, V = 3576(3) A(3), Z = 4). In salt 1 the organic BET-TTF molecules are packed in orthogonal dimers, forming the first kappa phase observed for this donor. The analysis of the bond distances and the electronic and IR spectra suggests a degree of ionicity of 1/4 per BET-TTF molecule, in agreement with the stoichiometry of the salt. The electrical properties show that 1 is a semiconductor with a high room-temperature conductivity (11.6 S cm(-1)) and a low activation energy (45 meV), in agreement with the band structure calculations. The magnetic susceptibility of 1 shows, besides the paramagnetic contribution from the anion, a temperature-independent paramagnetism (TIP) of the Pauli type due to the electronic delocalization observed at high temperatures in the organic sublattice. This Pauli type paramagnetism is confirmed by the ESR spectra that also show a Dysonian line when the magnetic field is parallel to the conducting plane, typical of metallic and highly conducting systems. Salt 2 presents an unprecedented packing of the organic molecules that form zigzag tunnels where the anions and the solvent molecules are located. The stoichiometry indicates that all the BET-TTF molecules bear a charge of +1, and accordingly, 2 behaves as a semiconductor with a very low room-temperature conductivity. The magnetic properties of this salt indicate that the unpaired electrons on the organic molecules are strongly antiferromagnetically coupled, giving rise to a diamagnetic behavior of 2, as the nitroprusside anion is also diamagnetic.