X-ray crystal structure, magnetic and electric properties of TTF trimer-based salts of FeCl4-, [TTF7(FeCl4)2]

A new TTF trimer-based charge transfer salt, TTF7(FeCl4)(2), has been synthesized and characterized. It belongs to the monoclinic space group C2/m, M = 1812.75, a = 28.433(5), b = 16.524(3), c = 16.981(3) Angstrom, beta = 121.17(2)degrees, V = 6826(2) Angstrom(3) and Z = 4. The crystal structure shows the two types of layers O and I; the layer O is composed of two sets of TTF trimers orthogonal to each other, providing a two-dimensional interacting network of TTF molecules, while the layer I consists of TTF molecules and FeCl4 anions. The FeCl4 anions can interact magnetically with the TTF molecules in both the layers O and I because of the short S ... Cl distance. Single-crystal temperature-dependent conductivity measurements show that this material is a semiconductor with a room-temperature conductivity of 0.055 S cm(-1) and a thermal activation energy of 0.15 eV. The temperature dependence of magnetic susceptibilities indicates antiferromagnetic behavior based on FeCl4- anions and radical cations. Two EPR signals were observed for the microcrystals; the broader signal afforded a large temperature dependence of the g value ranging from 2.15 (292 K) to 1.86 (5 K).