2,4,5-Tri-4-pyridyl-1H-imidazole monohydrate

The title compound, C18H13N5·H2O, was synthesized by the condensation of pyridine-4-carbaldehyde and ammonium acetate, forming a multipyridyl ligand. In the crystal, molecules are linked into chains by O—H⋯N hydrogen bonds. The chains are linked by weak C—H⋯N interactions, generating a layer structure.

In 2,4,5-tri(4-pyridyl)imidazole three pyridyl groups are directly connected with the imidazole ring. The dihedral angles between the mean planes of pyridyl ring A and imidazole ring D is 11.6 (4)°, that of pyridyl ring B and imidazole ring D is 8.4 (3)°, and that of pyridyl ring C and imidazole ring D is 84.1 (3)°, suggesting that the plane of ring A and B are co-planar with ring D, but that ring C and ring D are almost vertical.
In the crystal lattice the molecules are linked by O-H···N hydrogen bonds, and by weak C-H···N interactions to generate a three-dimensional layer structure (Fig 2).

Experimental
A mixture of 2 g (0.018 mol) of 4-pyridinecarbaldehyde and 8 g (0.1 mol) of ammonium acetate was heated to 393 K with stirring 3 h. The reaction mixture was cooled, the precipitate was filtered off, washed with water, 5% solution of NaOH, and recrystallized from ethanol. Single crystals of 2,4,5-tri(4-pyridyl)imidazole suitable for X-ray analysis were obtained

Refinement
The H atoms of the pyridyl rings were constrainted as idealized aromatic CH groups. The H atoms of water, H1A and H1B, were located in a difference Fourier map and the O1-H1A and O1-H1B were restrained to 0.85Å, the H1A-H1Bwas restrained to 1.35Å. The proton on the imidazole N atom, H1C,was also located in a difference Fourier map and N1-H1C was restrained to 0.94Å. The U iso (H) was equal to 1.2 times that of the parent atoms for all H atoms.

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 Rfactors(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.