2-(4-Aminophenyl)-3,4,5,6-tetrahydropyrimidin-1-ium chloride

In the title compound, C10H14N3 +·Cl−, the tetrahydropyridinium ring of the cation, which adopts a slightly distorted envelope conformation, is disordered over two orientations with an occupancy ratio of 0.653 (5):0.347 (5). The amidinium fragment of the major conformer is twisted relative to the benzene ring by 22.5 (6)° and the two C—N bond lengths of this fragment are similar [1.3228 (16) and 1.319 (2) Å]. In the crystal, the chloride anions are involved in three N—H⋯Cl hydrogen bonds, which link the components into a two-dimensional hydrogen-bonded network parallel to (010).

In the title compound, C 10 H 14 N 3 + ÁCl À , the tetrahydropyridinium ring of the cation, which adopts a slightly distorted envelope conformation, is disordered over two orientations with an occupancy ratio of 0.653 (5):0.347 (5). The amidinium fragment of the major conformer is twisted relative to the benzene ring by 22.5 (6) and the two C-N bond lengths of this fragment are similar [1.3228 (16) and 1.319 (2) Å ]. In the crystal, the chloride anions are involved in three N-HÁ Á ÁCl hydrogen bonds, which link the components into a twodimensional hydrogen-bonded network parallel to (010).
The tetrahydropyrimidinium ring is disordered over two positions designated as A and B (Fig. 1). Their respective occupancies are 0.347 (5)/ 0.653 (5). While there is a formal double C=N bond in the neutral tetrahydropyrimidine, both C-N bonds in the cation are approximately equal. However, the positive charge is localized on the C7 atom, as confirmed by DFT calculations (Fig. 3). Such a delocalization poses a significant restraint to conformation of the tetra-  Table 1)
DFT calculations. The structure, obtained from the X-ray structural analysis was optimized without symmetry constrains by using MP2/6-31+G(d,p) level of theory implemented in the GAMESS program package (Schmidt et al., 1993) . Tight convergence criteria were used in the optimization. The calculation was checked for convergence and frequencies were calculated in order to prove that the optimized structure was the minimum. The optimized geometry shows agreement with experimental one (conformer B); only four bonds (N1-C1, N3-C7, C2-C3 and C5-C6) differ more than 3 e.s.d.'s.

Refinement
Hydrogen atoms were located from a difference Fourier map and refined as riding on their parent atoms. C-H bond lenghts were constrained to 0.93 and 0.97 Å for aromatic and methylene H atoms, respectively, while N-H bonds were constrained to 0.90 Å; U iso (H) = 1.2 U eq (C,N). Since the disordered atoms are very close to each other, they were refined with equal displacement ellipsoids using the command EADP in SHELXL97 (Sheldrick, 2008) for every pair of disordered atoms (A and B), except C9A and C9B which had their displacement parameters refined independently.

Figure 3
Mulliken charges calculated by DFT method.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (