¹H NMR (400 MHz, CDCl₃) δ 8.90 (s, 1H), 7.51 (s, 1H), 7.01 (s, 1H), 6.53 (s, 1H); ¹³C NMR (101 MHz, CDCl₃) δ 159.5 (s), 143.7 (s), 139.3 (s), 112.2 (s), 112.0 (s), 108.9 (s). HRMS (EI): calculated for C₇H₄N₂O₄: 180.0171; found: 180.0169.