1,1'-Methyl­enedipyridinium tetra­chloridocuprate(II) and bis­[tetra­chloridoaurate(III)] hybrid salts by X-ray powder diffraction

In order to explore the potential propensity of the 1,1'-methyl­enedipyridinium dication to form organic-inorganic hybrid ionic compounds by reaction with the appropriate halide metal salt, the organic-inorganic hybrid salts 1,1'-methyl­enedipyridinium tetra­chloridocuprate(II), (C₁₁H₁₂N₂)[CuCl₄], (I), and 1,1'-methyl­enedipyridinium bis­[tetra­chloridoaurate(III)], (C₁₁H₁₂N₂)[AuCl₄]₂, (II), were obtained by treatment of 1,1'-methyl­enedipyridinium dichloride with CuCl₂ and Na[AuCl₄], respectively. Both hybrid salts were isolated as pure compounds, fully characterized by multinuclear NMR spectroscopy and their mol­ecular structures confirmed by powder X-ray diffraction studies. The crystal structures consist of discrete 1,1'-methyl­enedipyridinium dications and [CuCl₄]^2- and [AuCl₄]^- anions for (I) and (II), respectively. As expected, the dications form a butterfly shape; the Cu^II centre of [CuCl₄]^2- has a distorted tetra­hedral configuration and the Au^III centre of [AuCl₄]^- shows a square-planar coordination. The ionic species of (I) and the dication of (II) each have twofold axial symmetry, while the two [AuCl₄]^- anions are located on a mirror-plane site. Both crystal structures are stabilized by inter­molecular C-H...Cl hydrogen bonds and also by Cl...[pi] inter­actions. It is noteworthy that, while the average inter­molecular centroid-centroid pyridinium ring distance in (I) is 3.643 (8) Å, giving strong evidence for noncovalent [pi]-[pi] ring inter­actions, for (II), the shortest centroid-centroid distance between pyridinium rings of 5.502 (9) Å is too long for any significant [pi]-[pi] ring inter­actions, which might be due to the bulk of the two [AuCl₄]^- anions.