Polymorph β of 1H-benzimidazole

Abstract

A second ortho­rhom­bic polymorph (β) of 1H-benzimidazole, C7H6N2, metastable at room temperature, has been obtained. It has a melting point of 431 K and a crystal density of 1.27 Mg m−3. At room temperature, the crystals transform into the well known ortho­rhom­bic α form, with a melting point of 445 K. In both polymorphs, benzimidazole mol­ecules are connected into polymeric chains via N—H⋯N hydrogen bonds. However, the mode of aromatic ring inter­actions differs significantly in the two crystalline forms. In the α form, the mol­ecules show edge-to-face inter­actions, whereas in the new β form, a sandwich–herringbone arrangement of the aromatic mol­ecules is observed.