Polymorphism in Hybrid Organic−Inorganic Bilayered Magnetic Conductors (BEDT-TTF)₃(Fe^IIICl₄)₂, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene

Two polymorphic hybrid organic−inorganic bilayered magnetic conductors (BEDT-TTF)3(FeCl4)2 (I and II) (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) were obtained by the diffusion method. I crystallizes in a monoclinic system with cell parameters: a = 55.9187(7) Å, b = 6.7424(1) Å, c = 14.9057(3) Å, β = 101.056(1)°, V = 5515.5(2) Å3, Z = 4, and C2/c at 290 K, and it transforms to a triclinic system at 220 K: a = 13.4440(2) Å, b = 14.6761(2) Å, c = 28.1529(5) Å, α = 100.738(1)°, β = 96.875(1)°, γ = 90.017(1)°, V = 5416.8(2) Å3, Z = 4 and P1̅ which is stable to 110 K. II crystallizes in a triclinic system with cell parameters: a = 6.7396(3) Å, b = 9.9640(5) Å, c = 21.132(1) Å, α = 79.536(2)°, β = 81.032(2)°, γ = 81.066(3)°, V = 1367.3(1) Å3, Z = 1, and P1̅ at 290 K. They both contain two donor layers having formal charge of BEDT-TTF+0.5 in layer-A and BEDT-TTF+1.0 in layer-B. The donor arrangements in layer-A are δ-type in I and β′-type in II, while the donor arrangements in layer-B and anion arrangements in I and II are also different. Layer-A is separated from layer-B by FeCl4−. The energy band calculation indicates a Peierls-like metal−insulator transition in the transverse direction at 220 K in I (σ300Κ = 120 S·cm−1), and a Mott insulating state in II (σ300Κ = 10−2 S·cm−1 and Eα = 0.2 eV). The presence of π−d interactions between donors and anions results in the magnetic anomalies observed at 4.8 K in I and 2.7 K in II.