New BEDT-TTF Salts Incorporating the Hydrogen Dichloride (HCl₂^-) Anion

Salts of the π-donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) have been isolated with hydrogen dichloride (HCl₂^-) as the counterion. Two phases were obtained, α′-BEDT-TTF₂(HCl₂) (1) and ∈-BEDT-TTF(HCl₂) (2), by electrocrystallization from solvent mixtures containing ClCH₂COCl. Like previously described α′-BEDT-TTF₂X salts, 1 contains sheets of twisted BEDT-TTF dimers, and conductivity and magnetic susceptibility are consistent with a description of nearly localized (BEDT-TTF)₂⁺ radicals. Salt 2, space group C2/m, undergoes an anion ordering structural phase transition near 200 K, resulting in a new low-temperature phase ∈′-BEDT-TTF(HCl₂) (3) with space group P2₁/c. Below 170 K, 3 undergoes a magnetic phase transition seen in electron paramagnetic resonance data. The HCl₂^- ion is linear in 1 but bent in 2 and 3. α′-(BEDT-TTF)₂(HCl₂), 1, crystallizes in the P2/c space group with a = 7.7023(1) Å, b = 6.6140(1) Å, c = 30.1077(6) Å, β = 96.506(1)°, V = 1523.90(4) ų, and Z = 2. ∈-BEDT-TTF(HCl₂), 2, crystallizes in the C2/m space group with a = 12.9687(8) Å, b = 11.6077(8) Å, c = 5.6949(4) Å, β = 104.688(1)°, V = 829.28(10) ų, and Z = 2. ∈′-BEDT-TTF(HCl₂), 3, belongs to the P2₁/cspace group with a = 12.7112(1) Å, b = 11.5778(2) Å, c = 11.3583(1) Å, β = 101.194(1)°, V = 1639.77(3) ų, and Z = 4.