Key indicators: single-crystal X-ray study; T = 297 K; mean (C-C) = 0.003 Å; R factor = 0.051; wR factor = 0.132; data-to-parameter ratio = 12.9.The structure of the title compound, C 13 H 12 N 3 + ÁClO 4 À , reveals a twofold axis through the ring N and para-C atoms; a twofold rotation axis also passes through the Cl atom. The structure of the organic fragment is similar to that of homologous heterocyclic systems. The organic cations and perchlorate anions self-assemble in the solid state through C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, leading to a two-dimensional layer parallel to the (112) plane. The layers are stacked along the c axis through offsetinteractions between cations from different layers (the distance between the planes through two cations is 3.35 Å ), resulting in a three-dimensional supramolecular architecture. ExperimentalCrystal data C 13 H 12 N 3 + ÁClO 4 À M r = 309.71 Monoclinic, C2=c a = 15.122 (3) Å b = 13.477 (3) Å c = 6.6922 (13) Å = 101.21 (3) V = 1337.8 (5) Å 3 Z = 4 Mo K radiation = 0.31 mm À1 T = 297 (2) K 0.33 Â 0.29 Â 0.19 mm Data collection Bruker SMART APEX CCD areadetector diffractometer Absorption correction: multi-scan (SHELXTL; Bruker, 2001) T min = 0.906, T max = 0.934 7044 measured reflections 1378 independent reflections 1271 reflections with I > 2(I) R int = 0.034

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