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) A, b = 5.102(3) A, c = 14.401(8) A, β = 96.859(10)°, V = 934.3(9) A3, 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) A, b = 4.815(2) A, c = 17.816(7) A, β = 92.329(8)°, V = 1223.4(9) A3, Z = 2. For compound 2, one dimensional chain structure is formed through hydrogen bonds of N–H+···O−. The chains extend in two crossed directions. These adjacent 1D parallel chains form 2D network structure under the interchain CH2–π associations. There also exist interchain CH2···O interactions between crossed chains. Under these weak interactions, 2 displays 3D network structure. Due to the weak interactions, the complex displays 3D network structure.