Mr= 153.2, orthorhombic, P212121, a= 7.370(1), b=8.148(1), c=12.847(1)A, V= 771.5(1) A 3, Z=4, D x=1.319Mgm -3, 2(CuKa) =1.5418A, #=0.69mm -1, F(000)=328, T= 289 (1)K. Final R =0.045 for 685 observed reflections. The pyrrolizidine nucleus is planar within +0.04 (1) A except for C(6) which lies on the opposite side of the plane from the C(7)-hydroxyl oxygen substituent; bond lengths in ring B indicate extensive electron delocalization. Hydrogen bonds involving only the hydroxyl substituents link the molecules into sheets perpendicular to the c axis. M r = 497.49, monoclinic, C2/c, a = 39.306(14), b=6.974(3), c=21.291(8)A, fl= 121.83 (3) °, V= 4959 (4) A 3, Z = 8, D m = 1.33 (2), Dx= 1.33 g cm -3, 2(Cu Ka) = 1.54178 .A, # = 8.51cm -~, F(000)=2096, room temperature, R= 0.046 for 1700 observed reflections. The imidazole ring is protonated and is in the same plane as the benzene ring containing the nitro group. Two imidazole rings related by the center of symmetry are linked to each other through four water molecules at the H-N site. The molecules are packed in sheets parallel to the ac plane. The hydration or dehydration of the crystal structure is related to the color change of the crystal