2-(4-tert-Butylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline sesquihydrate

In the title compound, C23H20N4·1.5H2O, the mean planes of the imidazo[4,5-f][1,10]phenanthroline system and the benzene ring make a dihedral angle of 21.76 (2)°. One water O atom lies on a twofold rotation axis. The organic molecules and water molecules are linked via N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds. Weak intermolecular C—H⋯N hydrogen bonds and π–π stacking interactions between inversion-related phenanthroline rings complete the three-dimensional hydrogen-bonding network in the crystal structure. The stacking distance is short at 3.513 (2) Å and the perpendicular distance between the rings is 3.355 Å. The three methyl groups are disordered over two positions, with a site-occupancy ratio of 0.875 (14):0.125 (14).

The three methyl groups are disordered over two positions, with a site occupancy ratio of ca 7:1.
Experimental 1,10-Phenanthroline-5,6-dione (0.84 g, 0.004 mol) and ammonium acetate (3.1 g, 0.04 mmol) were dissolved in 40 ml of hot glacial acetic acid. While the mixture was stirred, a solution of 4-tert-butylbenzaldehyde (0.65 g, 0.004 mmol) in 10 ml of glacial acetic acid was added dropwise to the mixture. The mixture was heated at 363 K for 3 h and was then poured in 200 ml of water. The solution was neutralized with ammonia to pH=8 and was then cooled to room temperature. The precipitate was filtered off and recrystallized from dillute ethanol solution to give the title compound (I). Crystals suitable for X-ray diffraction were grown by slow evaporation of the EtOH solutions at room temperature.

Refinement
The methyl groups were found to be disordered over two orientations. The occupancies of the disordered positions C21/ C21', C22/C22' and C23/C23' were refined to 0.875 (14)/0.125 (14). Suitable restraints were applied to the C-C distances involving the disordered atoms. The methyl H atoms were constrained to an ideal geometry with C-H distances of 0.96 Å and U iso (H) = 1.5 U eq (C), but each group was allowed to rotate freely about its C-C bond. Other H atoms were placed in geometrically idealized positions and constrained to ride on their parent C atoms, with C-H distances of 0.93 to 0.97 Å, and with U iso (H) = 1.2 U eq (C). All H atoms on N atoms were positioned geometrically and refined as riding atoms, with N-H = 0.86 Å and U iso (H) = 1.2 U eq (N). The H atoms of the waters were located in a Fourier map following isotropic refinement. In the absence of significant anomalous scattering effects, Friedel related intensity reflections were averaged.
supplementary materials sup-2 Figures Fig. 1. View of the molecular structure of (I), showing the atomic numbering. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are indicated by dashed lines. The three disordered methyl groups were omitted for clarity.

Special details
Geometry. All e.s. 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.