Hydrazine bridged imidazole (1) and its fumarate salt (2) have been synthesized and structurally characterized. Hydrazine bridged imidazole (1) crystallizes in the monoclinic, space group P2(1)/n, with a = 12.809(7) Å , b = 5.102(3) Å , c = 14.401(8) Å , b = 96.859(10)°, V = 934.3(9) Å 3 , Z = 2. In 1, the two imidazolyl rings are located anti-parallely above and below the benzene planes, respectively. This arrangement leads the imidazolyl rings to be in the trans conformation. In addition at each C=N bond, the larger groups linked to C and N atoms are located in the same side of the double bond, thus in the solid state the conformation of the bis-imidazole (1) is E, E. Compound 2 crystallizes in the monoclinic, space group P2(1)/n, with a = 14.272(6) Å , b = 4.815(2) Å , c = 17.816(7) Å , b = 92.329(8)°, V = 1223.4(9) Å 3 , Z = 2. For compound 2, one dimensional chain structure is formed through hydrogen bonds of N-H ? ÁÁÁO -. The chains extend in two crossed directions. These adjacent 1D parallel chains form 2D network structure under the interchain CH 2 -p associations. There also exist interchain CH 2 ÁÁÁO interactions between crossed chains. Under these weak interactions, 2 displays 3D network structure.