Bis[4-(dimethylamino)pyridinium] octaaquachloridolanthanum(III) tetrachloride trihydrate

The title organic–inorganic salt, (C7H11N2)2[LaCl(H2O)8]Cl4·3H2O, consists of two 4-(dimethylamino)pyridinium and one [La(H2O)8Cl]2+ cations, four chloride anions and three solvent water molecules. In the crystal, the various units are connected by N—H⋯Cl, O—H⋯Cl, O—H⋯O and N—H⋯O hydrogen bonds, forming a network of alternating organic and inorganic layers. The 4-(dimethylamino)pyridinium cations stack along the c axis, while the inorganic layers lie parallel to the ac plane. The chloride anions are located between these entities, forming hydrogen bonds with the NH atom of the pyridinium ions and the water molecules. There are also C—H⋯Cl hydrogen bonds present involving one of the 4-(dimethylamino)pyridinium cations, resulting in the formation of a three-dimensional supramolecular architecture.

Technical support (X-ray measurements) from the Laboratory of Coordination Chemistry, UPR-CNRS 8241, Toulouse, is gratefully acknowledged. Organic-inorganic hybrid compounds are of great interest because of their special magnetic (Cui et al., 2000), electronic (Lacroix et al., 1994) and optoelectronic properties (Chakravarthy & Guloy, 1997). It is expected that the packing interactions that govern the crystal organization will be influenced by the features of the cations and anions, which in turn will affect specific properties of the solids. The supramolecular networks become especially interesting when the cation and anion can participate in hydrogen-bonding. As part of a study of the effect of cations and anions on the crystal structures of organic-inorganic compounds, we report herein on the crystal structure of the title compound. This type of hybrid material generally exhibits a structure consisting of alternating organic-inorganic layers, characterized by isolated anions as found with other compounds involving 4-(dimethylamino)pyridinium (Chao et al., 1977;Mayr-Stein & Bolte, 2000;Ng, 2008, 2009;Koon et al., 2009).
The title structure contains three cations, one inorganic [La(H 2 O) 8 Cl] 2+ cation and two independent monoprotonated 4-(dimethylamino)pyridinium cations, four chloride anions and three water molecules (Fig. 1). Atom La1 is coordinated by eight water molecules with distances ranging from 2.510 (1) to 2.588 (2) Å, and by one chloride ion with La1-Cl5 = 2.8829 (6) Å. The overall structure consists of layers stacked along the c axis. The chloride anions are located between the organic entities forming hydrogen bonds with the NH atoms of the pyridinium ions and the water molecules (Table 1).
Each Clanion accepts hydrogen bonds which can be divided into two groups. The first group involves hydrogen bonds linking Cl4with two organic cations via the pyridinium N4-H4A H atom (Table 1), generating centrosymmetric R 2 2 (4) motifs (Bernstein et al., 1995) along the c axis at y = 1/2. The second 4-(dimethylamino)pyridinium molecule is linked to one [La(H 2 O) 8 Cl] 2+ cation through an intermolecular N2-H2A···Cl5 i hydrogen bond [symmetry code: (i) x -1, y + 1, z] which can be described by the graph-set motif D(3). The second type of hydrogen bond, in which the Clanion is the acceptor, is a linkage between the water molecules (free and coordinated) and the Clanion. The inorganic [La(H 2 O) 8 Cl] 2+ cations are indirectly linked via Clanions through intermolecular O-H···Cl and O-H···O hydrogen bonds generating cycles R 2 2 (8) and R 6 2 (12), which connect cationic and anionic entities ( Fig. 2 and Table 1).
In the 4-(dimethylamino)pyridinium cations the N-C bond linking the dimethylamino substituent to the pyridinium ring is characteristically short [1.321 (3) and 1.324 (3)Å]. The dimethylamino group lies close to the plane of the pyridinium ring with a dihedral angle, between the pyridinium and the dimethylamine plane (C/N/C atoms), of 3.5 (3) and 2.0 (3)°.
On the structural level, the atomic arrangement of this material consists of a network of alternating organic-inorganic layers. The chloride anions are located between these entities forming hydrogen bonds with the NH atoms of the pyridinium ions and the water molecules. There are also C-H···Cl interactions present (Table 1)  Experimental 4-(Dimethylamino)pyridine (1 mmol, 0.08g) and hydrochloric acid (1M) were added slowly to a solution of LaCl 3 .6H 2 O (1mmol, 0.08g). The mixture was refluxed at 353 K for about 1 h and then cooled to room temperature. Slow evaporation of the solvent at room temperature lead to the formation of colourless plate-like crystals of the title compound.

Refinement
The H atoms of the coordinated water molecules were located in difference Fourier syntheses and were initially refined using distance restraints: O-H = 0.85 (2) Å, and H···H = 1.40 (2) Å, with U iso (H) = 1.5U eq (O). In the final cycles of refinement they were constrained to ride on their parent O atoms. The N-bound H atoms were located in a difference Fourier map but like the C-bound H atoms they were included in calculated positions and treated as riding atoms: N-H = 0.86 Å, C-H = 0.93 and 0.96 Å for CH and CH 3 H atoms, respectively, with U iso (H) = 1.5U eq (C) for the methyl groups and = 1.2U eq (N,C) for the other H atoms.

Bis[4-(dimethylamino)pyridinium] octaaquachloridolanthanum(III) tetrachloride trihydrate
Crystal data (C 7  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.76 e Å −3 Δρ min = −1.03 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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 > 2sigma(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.