4-(Naphthalene-2-carboxamido)pyridin-1-ium thiocyanate–N-(pyridin-4-yl)naphthalene-2-carboxamide (1/1)

The asymmetric unit of the title compound, C16H13N2O+·NCS−·C16H12N2O, contains two N-(pyridin-4-yl)naphthalene-2-carboxamide molecules, both are partially protonated in the pyridine moiety, i.e. the H atom attached to the pyridine N atom is partially occupied with an occupancy factor of 0.61 (3) and 0.39 (3), respectively. In the crystal, protonated and neutral N-(pyridin-4-yl)naphthalene-2-carboxamide molecules are linked by N—H⋯N hydrogen bonding; the thiocyanate counter-ion links with both protonated and neutral N-(pyridin-4-yl)naphthalene-2-carboxamide molecules via N—H⋯S and N—H⋯N hydrogen bonding. The dihedral angles between the pyridine ring and naphthalene ring systems are 11.33 (6) and 9.51 (6)°, respectively. π–π stacking is observed in the crystal structure, the shortest centroid–centroid distance being 3.5929 (8) Å. The crystal structure was determined from a nonmerohedral twin {ratio of the twin components = 0.357 (1):0.643 (1) and twin law [-100 0-10 -101]}.


Experimental
A solution of naphthalene 2-carbonyl chloride (0.01 mol) in anhydrous acetone (80 ml) was added dropwise to a suspension of dry sodium thiocyanate (0.01 mol) in acetone (50 ml) and the reaction mixture was refluxed for 45 min.
After cooling to room temperature, a solution of 4-aminopyridine (0.01 mol) in anhydrous acetone (25 ml) was added and the resulting mixture refluxed for 2 h. Hydrochloric acid (0.1 N, 400 ml) was added, and the solution was filtered.
H atoms attached to C atoms were positioned with idealized geometry and were refined isotropic with U eq (H) set to 1.2 times of the U eq (C) using a riding model with C-H = 0.95 Å. H atoms attached to N atoms were positioned with idealized geometry and were refined isotropically with U eq (H) set to 1.2 times of U eq (N) using a riding model with N-H

Figure 1
The molecular structure of the title compound with labeling and displacement ellipsoids drawn at the 30% probability level. The dashed line denotes the hydrogen bond between the neutral and protonated moieties.

Figure 2
The molecular packing of the title compound, viewed down c axis. The dashed lines denote hydrogen bonds.

4-(Naphthalene-2-carboxamido)pyridin-1-ium thiocyanate-N-(pyridin-4-yl)naphthalene-2-carboxamide (1/1)
Special details Experimental. CrysAlis RED, (Agilent, 2011) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm (Clark & Reid, 1995). 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.