4-(Dimethylamino)pyridinium tetrachloridoferrate(III)

The title salt, (C7H11N2)[FeCl4], consists of one essentially planar (the r.m.s. deviation for all non-H atoms being 0.004 Å) 4-(dimethylamino)pyridinium cation and a tetrahedral tetrachloridoferrate(III) anion. The cations and anions are arranged in layers parallel to (010). Besides electrostatic interactions, the crystal packing features N—H⋯Cl and C—H⋯Cl hydrogen bonds between cations and anions, forming a three-dimensional network.

The title salt, (C 7 H 11 N 2 ) [FeCl 4 ], consists of one essentially planar (the r.m.s. deviation for all non-H atoms being 0.004 Å ) 4-(dimethylamino)pyridinium cation and a tetrahedral tetrachloridoferrate(III) anion. The cations and anions are arranged in layers parallel to (010). Besides electrostatic interactions, the crystal packing features N-HÁ Á ÁCl and C-HÁ Á ÁCl hydrogen bonds between cations and anions, forming a three-dimensional network.
The asymmetric unit of (I) consists of tetrahedral [FeCl 4 ]anions and one protoned 4-(dimethylamino)pyridine cation that is essentially planar; its r.m.s. deviation for all non-H atoms is 0.0043 Å, with a maximum deviation from the mean plane of -0.0094 (2) Å for the C4 atom. The packing of the ionic entities is realized by alternating layers of cations and anions parallel to (010) whereby the dimethylaminopyridinium molecules are oriented in a zig-zag fashion parallel to the (210) and (210) planes, respectively (Fig. 2). The crystal packing is stabilized by N-H···Cl and C-H···Cl hydrogen bonds involving the chloride atoms of the anions as acceptors (Table 1, Fig. 3). All these interactions link the layers together, forming a three-dimensional network and reinforcing the cohesion of the ionic structure.
A similar complex with a 4-(dimethylamino)pyridinium cation but a different metal-based anion, viz.
Experimental 4-(dimethylamino)pyridine and iron(III) chloride hexahydrate were mixed in an equimolar ratio in acidified water (HCl, 37% wt ). The solution was kept at room temperature for ten days after which crystals suitable for X-ray diffraction could be isolated.

Refinement
H atoms were localized from Fourier maps but introduced in calculated positions and treated as riding on their parent C atoms with C-H = 0.98 Å (methyl) or C-H = 0.95 Å (aromatic), and with U iso (H) = 1.2 U eq (C aryl )and U iso (H) = 1.5 U eq (C methyl ). H3 attached to the pyridinium N atom was refined without constraints.

4-(Dimethylamino)pyridinium tetrachloridoferrate(III)
Crystal data (C 7  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 R-factors(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.