The reactions of MoCl5 with 2-(2′-thienyl)benzimidazole (I) and 2-(2′-thienyl)-1-(2′-thienylmethyl)benzimidazole (II) have been carried out. From the reaction of (I) a molybdenum complex was obtained, which surprisingly was found to contain (II), by X-ray diffraction analysis. Crystals of the complex are triclinic, space group P, with unit-cell dimensions, a= 10.524(2), b= 14.352(4), c= 10.213(2)A, α= 95.49(1), β= 100.68(3), γ= 118.79(1)°, Z= 1, and R= 0.076 for 2 129 observed reflections. The structure has been solved by direct methods and refined by least squares. It consists of centrosymmetric tetramers, [{MoClO2(OEt)}4]2–, surrounded by 2-(2′-thienyl)-1-(2′-thienylmethyl)benzimidazolium cations linked to the tetramers through O ⋯ HN+ bridges.