One Dimensional Face-to-Face Stacking of Anderson–Evans [Cr(OH)6Mo6O18]3-Polyoxometalate Anion: Synthesis, Structure, and Physical Properties of (BEDT-TTF)4[Cr(OH)6Mo6O18] 2H2O

Abstract

The synthesis, structural and magnetic characterizations of a new charge transfer salt (BEDT-TTF)4[Cr(OH)6Mo6O18]⋅2H2O based on the planar paramagnetic Anderson–Evans polyoxometalate are reported. Structural parameters: T=293 K, triclinic (P $$\bar 1$$ ), a=5.9545(2) A, b=16.3767(6) A, c=21.8643(6) A, α=110.829(2)°, β=91.262(2)°, γ=98.129(1)°, Z=1, R=0.0540. The crystal structure is characterized by a face-to-face stacking of the anions giving rise to a one-dimensional inorganic chain which develops along the a direction. The organic layers contain two crystallographically independent BEDT-TTF dimers that form alternating stacks along the b direction. This organic chain is perpendicular to the inorganic chains. The charges on BEDT-TTF dimers are deduced to +1.2(1) and +1.7(1) on the basis of the intramolecular bond lengths. The EPR spectrum at 2.5 K is characterized by the superposition of BEDT-TTF•+ and [CrIII(OH)6Mo6O18]3− signals. The static susceptibility can be fitted by the Curie–Weiss law down to 1.9 K and the magnetic moment at 300 K is estimated to 4.21μ B , suggesting the uncorrelated spin system with BEDT-TTF•+ (S=1/2) and CrIII (S=3/2) ions. This interpretion is consistent with the charge disproportionation on BEDT-TTF dimers along the stack, which is supported by the refined molecular structure and is closely related to the insulating behavior (<10−9S⋅cm−1 at RT).