Synthesis, crystal structure, and characterization of charge-transfer salt: (BEDT-TTF)5[Fe(C2O4)3]·(H2O)2·CH2Cl2 (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene)

Abstract

The synthesis, crystal structure, Raman spectra, XP spectra, conductivity and magnetism of a charge-transfer salt of BEDT-TTF and oxalato-metalate: (BEDT-TTF)₅Fe(C₂O₄)₃(H₂O)₂CH₂Cl₂ (1) are described and interpreted. Electrochemical oxidation of neutral BEDT-TTF in the presence of (Et₄N)₃Fe(C₂O₄)₃ in CH₂Cl₂ solution yields crystals of 1. 1 crystallizes in triclinic form with cell parameters: a = 11.0197(1)Å, b = 11.5010(2) Å, c = 35.2773(5) Å, α = 89.1256(4)°, β = 85.2348(5)°, γ = 70.0039(4)°, V = 4186.5(1) ų, Z = 2, P in 180 K. 1 is different from the well known charge-transfer salt (BEDT-TTF)₄AM(C₂O₄)₃S (A = K⁺, NH₄⁺ and H₃O⁺, S = solvent) in composition and crystal structure. Two donor layers and anion layers stack alternately along the c axis in 1. There is one enantiomer in an anion layer and the crystal remains racemized. The solvent molecule H₂O bonds to two anions through hydrogen bonds and CH₂Cl₂ exists in the cavity of the parallelogram formed by anions but not a pocket of honeycomb of [AM(C₂O₄)₃]²⁻ as in (BEDT-TTF)₄AM(C₂O₄)₃S. The formal charge of donor molecules was assigned to +0.5 and +1.0 from bond lengths in TTF core and corresponded to Raman and XP spectra. 1 is a paramagnetic semiconductor with σ_rt = 4 S cm⁻¹.