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Structural Investigations and Thermal Behavior of (EMIm)[Cr(C 2 O 4 ) 2 ]·2H 2 O [1‐Ethyl‐3‐methylimidazolium Chromium(III) Dioxalate Dihydrate]
Author(s) -
Kahlenberg Volker,
Wertl Waltraud,
Többens Daniel M.,
Schottenberger Herwig
Publication year - 2011
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201100109
Subject(s) - triclinic crystal system , crystallography , octahedron , crystal structure , chromium , hydrogen bond , molecule , chromate conversion coating , chemistry , oxalate , inorganic chemistry , organic chemistry
The 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) Å 3 . The crystal structure was solved by direct methods and refined (using anisotropic displacement parameters for all non‐hydrogen atoms) to a final residual of R 1 = 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(C 2 O 4 ) 2 (H 2 O) 2 – anions, respectively. The two crystallographically independent Cr(C 2 O 4 ) 2 (H 2 O) 2 octahedra reside on centers of symmetry (Wyckoff sites 1 a and 1 f ). 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 Cr 2 O 3 and Cr 3 C 2 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.