Structural Investigations and Thermal Behavior of (EMIm)[Cr(C2O4)2]·2H2O [1‐Ethyl‐3‐methylimidazolium Chromium(III) Dioxalate Dihydrate

Abstract

AbstractThe crystal structure of EMIm diaquobis(μ‐oxalato)chromate(III) (1‐ethyl‐3‐methylimidazolium chromium(III) dioxalate dihydrate) was determined from X‐ray single crystal diffraction studies. A pale violet crystal of good optical quality was used for the structure determination at –100(2) and 25(2) °C. The basic crystallographic data for the low temperature structure are as follows: triclinic symmetry, space group P$\bar{1}$ , a = 7.6202(8) Å, b = 9.7668(9) Å, c = 10.7171(11) Å, α = 109.257(9)°, β = 90.494(8)°, γ = 105.685(8)°, V = 720.75(1) Å3. The crystal structure was solved by direct methods and refined (using anisotropic displacement parameters for all non‐hydrogen atoms) to a final residual of R1 = 0.039 for 2062 independent observed reflections [I > 2σ(I)]. The compound is built up from alternating layers parallel to (010) containing (EMIm)+ cations or Cr(C2O4)2(H2O)2– anions, respectively. The two crystallographically independent Cr(C2O4)2(H2O)2 octahedra reside on centers of symmetry (Wyckoff sites 1a and 1f). The corners of the octahedra consist of four oxygen atoms from two oxalate groups and two additional water molecules. EMIm+ cations provide linkage between different octahedral layers by hydrogen bridging. The water molecules in turn form hydrogen bonds with adjacent octahedra within the same layer. According to DTA/TG experiments the present compound shows several thermal processes in the range between room temperature and 1000 °C. However, pyrolysis is reproducibly yielding pure inorganic composites, qualifying this novel organic‐inorganic hybrid salt also as a stable precursor for nanoscalar ceramic materials. The final product consists of a distinct mixture of Cr2O3 and Cr3C2 in the molar ratio of 1:1. Concomittant oxide and carbide formation is an unprecedented disintegration pathway of the thermal treatment of oxalatochromates without reducing atmosphere.