Crystal structure of bis(quinolin-1-ium) tetrachloridoferrate(III) chloride

The asymmetric unit of the title hybrid compound, (C9H8N)[FeCl4]Cl, comprises a tetrahedral tetrachloridoferrate(III) anion, [FeCl4]−, a Cl− anion and two quinolinium cations. There are N—H⋯Cl hydrogen-bonding interactions between the protonated N atoms of the quinolinium cations and the chloride anion, which together with π–π stacking between adjacent quinolinium rings [centroid-to-centroid distances between C6 and C5N rings in adjacent stacked quinolinium cations of 3.609 (2) and 3.802 (2) Å] serve to hold the structure together.


S1. Comment
Hybrid compounds are one of the important categories of materials. They have received much attention in research areas including nonlinear optics, second harmonic generation (SHG), third harmonic generation (THG) and optical switching [Bouchouit et al. (2008);Bouchouit, et al. (2010); Jayalakshmi et al. (2006); Sankar et al. (2007); Bouchouit et al. (2015)]. A considerable number of hybrid organic/inorganic compounds have been extensively studied for their promising properties. Crystals of many of these materials can be grown from aqueous solution (Khadri et al. (2013); Chen et al.
(2010); Prommon et al. (2012); Kruszynski et al. (2007)]. In the present work, a mixture of water and acetonitrile is used as solvent for the reaction of quinoline with iron (III) chloride and leads to the generation of crystals of bis-(quinolinium)tetrachloroferrate(III) chloride.
The asymmetric unit of the title hybrid compound consists of a tetrachloroferrate anion, (FeCl 4 ) − , a chloride Cl − anion and two quinolinium cations, (C 9 H 8 N) + (Fig. 1). The iron atom lies at the centre of a regular tetrahedron and it is coordinated to four Cl atoms with Fe-Cl bond lengths in the range 2.1862 (10) to 2.2013 (10) Å. The lengths of the C-C and C-N bonds in the two independent quinolinium cations are comparable to the related distances found in the literature. The quinolium cations stack on top of each other, held together by π-π interactions. The centroid to centroid distances between C 6 and C 5 N rings in adjacent stacked quinolinium cations are 3.609 (2) and 3.802 (2) Å.
The projection of the structure onto the a-c plane ( Fig. 2) shows the N-H···Cl hydrogen bonding interactions between the N-H groups of the quinolium cations and the Cl − anions which, together with the π-π interactions, serve to stabilize the structure.

S2. Experimental
Quinoline, C 9 H 7 N, (0.2 mmol) and iron (III) chloride, FeCl 3 , (0.1 mmol) were dissolved in a mixture of water (10 ml) and acetonitrile (10 ml) at ambient temperature over a period of approximately 30 minutes. After this period, a brown precipitate appeared which was removed by filtration. The filtrate was then left at room temperature until brown crystals appeared.

S3. Refinement
All non-H atoms were refined with anisotropic atomic displacement parameters. The remaining H atoms were localized

Bis(quinolin-1-ium) tetrachloridoferrate(III) chloride
Crystal data (C 9   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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq