3,4,7,8-Tetramethyl-1,10-phenanthrolin-1-ium nitrate monohydrate

In the crystal of the title compound, C16H17N2 +·NO3 −·H2O, the tetramethyl-1,10-phenanthrolinium cations, nitrate anions and lattice water molecules are all located on a mirror plane with the methyl H atoms of the cation equally disordered over two sites about the mirror plane. The cation, anion and water molecule are linked by O—H⋯O and N—H⋯O hydrogen bonds into a sheet parallel to the bc plane. π–π stacking between phenanthroline ring systems is observed in the crystal structure, the centroid–centroid distance being 3.4745 (6) Å.

Financial support from the National Natural Science Foundation of Henan Educational Committee, China (2011 C550002) is gratefully acknowledged.
The numbering scheme of (I) is given in Fig. 1, and the selected bond lengths and bond angles are provided in the cif file. The crystal contains one protonated 3,4,7,8-tetramethyl-1,10-1,10-phenanthroline cation, one nitrate anion and one water molecule. In the crystal structure, the cations, anions and water molecules are linked into two dimensional layers parallel to the bc plane by N-H···O and O-H···O hydrogen bonds (Table 1). Among them, N-H···O hydrogen bonds play a very important role in the formation of proton-transfer compounds. Additionally, the monoprotonated 3,4,7,8-tetramethyl-1,10-1,10-phenanthroline cations are parallel to each other in the crystal packing, showing π-π interactions (Fig. 2); the centroid-centroid distance is 3.4745 (6) Å.

Experimental
A aqueous solution (12 ml) of Tb(NO 3 ) 3 .6H 2 O (1 mmol) and 3,4,7,8-tetramethyl-1,10-phenanthroline (1 mmol) was stirred. The mixture was then transferred to a 25-ml Teflon reactor and kept at 433 K for 3 d under autogenous pressure, and then cooled to room temperature at a rate of 10 K h -1 . Colorless crystals of the title compound were obtained.

Refinement
The carbon-bound H atoms were placed in calculated positions and were included in the refinement in the riding model approximation, with C-H = 0.93 Å, U iso (H) = 1.2U eq (C aromatic) and C-H = 0.96 Å, U iso (H) = 1.5U eq (C methyl), respectively. The H atoms bound to O were located in a difference Fourier map, and refined as riding in their as-found relative positions with U iso (H) = 1.5U eq (O). The methyl H atoms are equally disordered over two sites about the mirror plane.

Figure 1
The molecular structure of the title compound, with atom labels and 30% probability displacement ellipsoids for non-H atoms.

Figure 2
π-π interactions between the neighboring aromatic rings of the title compound. Aromatic hydrogen atoms and methyl groups have been omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.22 e Å −3 Δρ min = −0.27 e Å −3 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.