Crystal structure of 1,1′-(pyridine-2,6-diyl)bis[N-(pyridin-2-ylmethyl)methanaminium] dichloride dihydrate

In the title compound,the two pyridine side arms are not coplanar, with the terminal pyridine rings subtending a dihedral angle of 26.45 (6)°. In the crystal, hydrogen bonds, intermolecular C—H⋯Cl contacts and a weak C—H⋯O interaction connect the molecule with neighbouring chloride counter-anions and lattice water molecules. The crystal packing also features by π–π interactions.


Chemical context
In recent years, ruthenium nitrosyl complexes have attracted considerable attention, essentially because of their interesting photoreactivity properties such as photochromism (Schaniel et al., 2007) and nitric oxide photorelease (Rose & Mascharak, 2008a). Ruthenium nitrosyl complexes could have desirable photoreactivity properties relying on the nature of the ligands. The utilization of polydentate ligands in coordination chemistry gives a few benefits over monodentate ligands, in particular because of the chelate effect (Martell, 1967). Multidentate pyridylamine derivative ligands can better control the stability (Afshar et al., 2004;Eroy-Reveles et al., 2007), solubility (Harrop et al., 2005) and structural characteristics of the resulting complex. More particularly, ruthenium complexes derived from pentadentate ligands are generally stable in physiological media (Halpenny et al., 2007;Rose & Mascharak, 2008b). This stability is necessary for (i) maintaining pharmacological activity, (ii) reducing the toxicity of free metal ions, and (iii) avoiding non-specific binding of partially connected metal ions with other biomolecules (Fry & Mascharak, 2011;Hoffman-Luca et al., 2009;Patra & Mascharak, 2003;Heilman et al., 2012). In the search for new systems, we report here the synthesis and crystal structure of 1,1 0 -(pyridine-2,6-diyl)bis[N-(pyridin-2-ylmethyl)methanaminium] dichloride dihydrate, which contains multiple coordination sites, and is thus an excellent candidate for forming stable ruthenium nitrosyl complexes.

Structural commentary
The title compound crystallizes in the triclinic space group P1 with one cationic molecule, two chloride anions, and two water ISSN 2056-9890 molecules per asymmetric unit. In the organic molecule, one terminal pyridine ring is almost co-planar with the central pyridine ring, making a dihedral angle of 4.56 (8) , while the second terminal pyridine ring is out of the plane with a dihedral angle between the two terminal pyridine rings of 26.45 (6) (Fig. 1). Bond lengths are within normal ranges and comparable with values found for a similar compound, N,N 0dialkyl-2,6-pyridinedimethanaminium (Kobayashi et al., 2006).

Supramolecular features
In the crystal, there are intermolecular hydrogen bonds (Table 1) and C-HÁ Á ÁCl and C-HÁ Á ÁO interactions between the molecules, the chloride anions and the lattice water molecules. The molecular structure of the compound is illustrated in Fig. 1 with hydrogen bonding indicated.

Figure 2
Views of the stacking along the a axis. Orange lines indicateinteractions. Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
Molecular structure showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are drawn as small spheres of an arbitrary radius. The orange dashed lines represent hydrogen bonds, C-HÁ Á ÁCl interactions and the weak C-HÁ Á ÁO interaction. [Symmetry codes: 2002) and 2,6-bis[(2-pyridiniomethyl)ammoniomethyl]pyridine tetrachloride monohydrate (IRODAV; Kobayashi et al., 2006). In those compounds, the two terminal pyridine rings are rotated out of the plane of the central pyridine ring with dihedral angles ranging from 63 to 89 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms of the water molecules and those bonded to nitrogen atoms were located in difference-Fourier maps and refined freely with isotropic displacement parameters. All C-bound H atoms were placed in calculated positions and refined using a riding model, with C-H = 0.95 (aromatic) or 0.99 Å (methylene) and with U iso (H) = 1.2U eq (C). For two similar N-H distances, a restraint was applied to make them approximately equal with an effective standard deviation of 0.02 Å .
Acta Cryst. (2021). E77, 1296-1298 research communications  Data collection: APEX3 (Bruker, 2012); cell refinement: APEX3 and SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT (Sheldrick 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 −0.0133 (