2-[(2-Hydroxybenzyl)amino]pyrazinium perchlorate–2-[(pyrazin-2-ylamino)methyl]phenol (1/1)

In the crystal structure of the title co-crystal, C11H12N3O+·ClO4 −·C11H11N3O, the perchlorate ion is disordered about a twofold rotation axis with the Cl atom located on the twofold rotation axis; the 2-[(2-hydroxybenzyl)amino]pyrazinium cation and the neutral 2-[(pyrazin-2-ylamino)methyl]phenol molecule are disordered about the rotation axis in a 1:1 ratio. These two are connected by a pyrazine–pyrazine N1—H⋯N4 hydrogen bond. The cation, whose two aromatic rings are twisted along the –CH2—NH– bond by 76.8 (1)°, is a hydrogen-bond donor to the perchlorate ion through the N atom of this link.


D-HÁ
Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2010 Salicylaldehyde condenses with romatic amines to yield Schiff bases, which serve as chelating ligands to a plethora of metal systems. These Schiff bases can be readily reduce to the corresponding secondary amines, which can also function as chelating ligands. Curiously, there are only few 2-(arylamino)methylphenols compared with the plethora of Schiff bases in the chemical literature. We have communicated the crystal structure of 2-{[(pyrazin-2-yl)amino]methyl}phenol (Gao & Ng, 2012). The compound reacts with half a molar equivalent of perchloric acid to form the co-crystal, C 11 H 12 N 3 O + .ClO 4 -.C 11 H 11 N 3 (Scheme I). The C 11 H 12 N 3 O + cation and the neutral C 11 H 11 N 3 O molecule are disordered about the same position in a 1:1 ratio. The crystal structure is interpreted in terms of the cation and neutral molecule being an N 1-pyrazine -H···N 4-pyrazine hydrogen bond. The cation, whose two aromatic rings are twisted along the -CH 2 -NH-bond by 76.8 (1) °, is hydrogen-bond donor to the perchlorate ion through the N atom of this link.

Experimental
A solution of 2-aminopyrazine (1 mmol) and salicylaldehyde (1 mmol) in toluene (50 ml) was heated for 10 h. The solvent was removed under vacuum, and the residue was reduced in absolute methanol by sodium borohydride. Light yellow crystals were obtained by recrystallization from methanol to which several drops of perchloric acid were added.

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H 0.93 to 0.97 Å, U iso (H) 1.2U eq (C)] and were included in the refinement in the riding model approximation.
The amino/pyrazinium and hydroxy H-atoms were located in a difference Fourier map, and were refined with distance restraints of N-H 0.88±0.01, O-H 0.84±0.01 Å; the temperature factors of the hydroxy amino H atoms were refined. The pyrazinium H atom should have only half-site occupancy; its temperature factor could not be refined and it was instead tied by a factor of 1.2 times.
The perchlorate ion is disordered about a twofold rotation axis; the chlorine atom itself is ordered. The four Cl-O distances were restrained to within 0.01 Å of each other as were the O···O distances. The temperature factors of the O atoms were tightly restrained to be nearly isotropic.