Crystal structure of 2,6-bis(2-hydroxy-5-methylphenyl)-4-phenylpyridinium bromide dichloromethane hemisolvate hemihydrate

The asymmetric unit in the structure of the title compound, C25H22NO2 +·Br −·0.5CH2Cl2·0.5H2O, comprises two pseudosymmetry-related cations, two bromide anions, a dichloromethane molecule and a water molecule of solvation. The two independent cations are conformationally similar with the comparative dihedral angles between the central pyridine ring and the three benzene substituent rings being 3.0 (2), 36.4 (1) and 24.2 (1)°, and 3.7 (2), 36.5 (1) and 24.8 (1)°, respectively. In the crystal, the cations, anions and water molecules are linked through O—H⋯O and O—H⋯Br hydrogen bonds, forming an insular unit. Within the cations there are also intramolecular N—H⋯O hydrogen bonds. Adjacent centrosymmetrically related aggregates are linked by π–π stacking interactions between the pyridine ring and a benzene ring in both cations [ring-centroid separations = 3.525 (3) and 3.668 (3) Å], forming chains extending across the ac diagonal. Voids between these chains are filled by dichloromethane molecules.

investigation on the synthesis of tridentate ligands (Kireenko et al., 2013;Huang et al., 2013Huang et al., , 2012 we obtained and studied the structure of the title compound, 2(C 25 H 22 NO 2 + ) . 2Br -. CH 2 Cl 2 . H 2 O, which may be regarded as a precursor of a promising ligand for the preparation of complexes of main group metal elements.
The asymmetric unit comprises two independent ligand cations, two bromide anions, a dichlormethane and a water molecule of solvation (Fig. 1). The cations are related by pseudotranslation (one half of the ab diagonal) and possess very similar geometrical parameters and conformations. The comparative dihedral angles between the central pyridine ring and the three benzene substituent rings are 3.0 (2), 36.4 (1), 24.2 (1)° and 3.7 (2), 36.5 (1), 24.8 (1)°, respectively for cations 1 and 2. Figure 2 represents the superposition of one independent cation with another shifted by x + 0.5, y + 0.5, z.
However, the bromide anions and the solvent water molecules do not satisfy this pseudosymmetry law.
In the crystal, the two crystallographically independent organic cations, the two bromide anions, and the water molecules are associated through moderately strong inter-species O-H···O and O-H···Br hydrogen bonds (Table 1), forming an insular framework (Fig. 3). Within the unit there are also intramolecular N-H···O hydrogen bonds. Adjacent centrosymmetrically-related aggregates are linked by π-π stacking interactions between the pyridine ring (N1-C31 in cation 1 and N2-C61 in cation 2) and a benzene ring (C11-C16 in cation 1 and C41-C46 in cation 2), giving ring centroid separations of 3.525 (3) and 3.668 (3) Å, respectively. This results in the formation of chains extending across the ac diagonal (Fig. 4).

S2. Experimental
The precursor of the title salt, 2,6-bis(2′-hydroxy-5′-methylphenyl)-4-phenylpyridine, was obtained from 2-hydroxy-5methylacetophenone via two parallel reactions: (a), condensation of the above acetophenone with benzaldehyde in the presence of NaOH and (b), iodination of above acetophenone in the presence of pyridine. The reaction of an equimolar mixture of the above intermediates with ammonium acetate led to formation of the precursor, with moderate yield.

S3. Refinement
All hydrogen atoms on aromatic atoms (both C and N) and methyl groups were placed in calculated positions and refined using a riding model, with C-H = 0.95-0.98 Å, with N-H = 0.88 Å, and with U iso (H) = 1.2 U eq (C,N) or 1.5 U eq (C) for methyl H atoms. A rotating model was applied to the methyl groups. All hydroxy and water hydrogen atoms were found from difference Fourier syntheses and refined with U iso (H) = 1.5 U eq (O) and restrained O-H distances (SADI). Three outliers (-1 1 1, 0 1 1, 1 1 0) were omitted from the data set in the last cycles of refinement.

Figure 1
The asymmetric unit in the structure of the title compound, with displacement ellipsoids shown at the 50% probability level. Hydrogen bonds are shown as dashed lines.
supporting information

Figure 2
The result of superposition of one independent cation with another shifted by an x + 1/2, y + 1/2, z operation.

Figure 3
Insular hydrogen bonded aggregates in the structure. Hydrogen bonds are shown as dashed lines. Suffix A indicates the symmetry operator -x + 1, y -1/2, -z + 1/2.  Chains formed by π-π stacking interactions between aromatic ring systems in adjacent H-bonded frameworks.

2,6-Bis(2-hydroxy-5-methylphenyl)-4-phenylpyridinium bromide dichloromethane hemisolvate hemihydrate
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.