1,2-Dimethyl-1,4-diazoniabicyclo[2.2.2]octane tetrachloridocuprate(II)

In the title compound, (C8H18N2)[CuCl4], torsion angles on the ethylene bridges of the 1,4-diazoniabicyclo[2.2.2]octane fragment are in the range 11.9 (5)–15.0 (5)° and the [CuCl4]2− anion has a strongly distorted tetrahedral geometry. The cation is connected to the anion via three-center N—H⋯Cl hydrogen bonds.


Comment
The synthesis and characterization of copper halides in which organic ligands link metal centres have attracted much attention. One of the reasons for that is the fact that the copper environment of these compounds can adopt different geometries: tetrahedral, pseudo-tetrahedral or square-planar (Corzo-Suárez et al., 1997). This coordination variety allows the study of the relationship between the different geometries and the structural and magnetic properties of these compounds.
The title compound at room temperature crystallizes in the centrosymmetric Pbca space group and is paraelectric. It contains an isolated distorted (compressed) tetrahedral [CuCl 4 ] 2anion, and a protonated (C 8 H 18 N 2 ) 2+ cation. In this salt, the N-H + group of the dication forms bifurcated hydrogen bond to two chloride ligands of the adjacent [CuCl 4 ] 2anion.
In [CuCl 4 ] 2anion distortion from tetrahedral geometry is typically measured by the value of the trans Cl-Cu-Cl angle and by the dihedral angle between CuCl 2 planes. In the present case, the two 'trans' angles are 131.30°(5) and 131. 22° (6) and the dihedral angle between the CuCl 2 planes is 65.72 (5).
The dielectric measurements (capacitance and dielectric loss measurements) on the powder samples pressed into tablets with a conducting carbon glue depositing on it, were carried out with an automatic impedance TongHui2828 Analyzer.
Dielectric permittivity of the compound was tested to investigate the possibility of ferroelectric phase transitions. In the temperature range 80-423 K no dielectric anomaly was observed revealing no phase transition in the studied temperature range.

Experimental
To a mixture of iodomethane (10 mmol) and chloroform (15 ml) at 273 K was added dropwise a chloroform solution of To the mixture of 1,2-methyl-1,4-diazabicyclo[2.2.2]octane iodide (4 mmol,1.07 g) and water (7 ml), concentrated hydrochloric acid (12 mmol) was added dropwise. Concentrated hydrochloric acid was also added dropwise to a mixture of CuCl 2 (2 mmol,0.341 g) and ethanol (5 ml). The two solutions were then mixed and stirred for 20 minutes. The resulting precipitate was dissolved in water. Yellow crystals suitable for X-ray analysis were formed after several weeks on slow evaporation of the solvent at room temperature (m.p. > 473 K).

Refinement
All the H atoms were positioned geometrically (C-H = 0.96-0.97 Å; N-H = 0.91 Å) and in the refinement process were allowed to ride on their carrier atoms with U iso (H) = 1.2U eq (C, N). Fig. 1. The molecular structure of the title compound, with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Dashed lines indicate hydrogen bonds.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.