Abstract

An electrolysis of bis(ethylenedithio)tetrathiafulvalene (ET) and a Mn-cluster in a 1,1,2-trichloroethane solution containing 10% (vol/vol) of ethanol yields black lustrous single crystals, β″-(ET)₃(MnCl₄)(1,1,2-C₂H₃Cl₃) based on the X-ray structural study. The crystal structure can be characterized as alternating two-dimensional donor sheets and insulating sheets made of isolated [MnCl₄]²⁻ ions and the 1,1,2-C₂H₃Cl₃ molecules. Every pair of the neighbouring donor molecules has a large displacement along both short and long molecular axes. A tight-binding band calculation suggests that this arrangement should lead to a weak but isotropic intermolecular interaction in the donor sheets, and this in turn should lead to a marginally metallic or semiconducting electronic structure. Although the polarized reflectance spectra and the temperature-dependent spin susceptibility derived from the EPR spectra on the single crystal indicate metallic nature, the electrical behaviour under atmospheric pressure is semiconductive with room temperature conductivity of 35 S cm⁻¹ and apparent activation energy of 0.023 eV. It exhibits a resistive hump with hysteresis at around 60 K, which could be associated with a structural transition demonstrated by a series of low temperature X-ray oscillation photographs. The magnetic susceptibility at 4.5–300 K does not exhibit any anomaly and is well reproduced by the Curie–Weiss model with Curie constant C/emu K mol⁻¹ = 3.89 and Weiss temperature θ/K  = −0.10. This magnetic behaviour can be quantitatively understood as the sum of Pauli paramagnetism of the π-electrons and the contribution from the local spins on the Mn(II) ions with d⁵-configuration (S = 5//₂). High pressure easily suppresses the increase in resistivity at low temperature, and the electrical behaviour is particularly sensitive to the first 3–5 kbar.