Crystal structure determination of mebendazole form A using high‐resolution synchrotron x‐ray powder diffraction data

The crystal structure determination of mebendazole form A, an anthelmintic drug, was performed for the first time by applying the DASH software program to synchrotron X‐ray powder diffraction data, and supported by a satisfying Rietveld fit. This polymorph of mebendazole crystallizes in a triclinic (P1¯) space group, with unit‐cell parameters a = 5.5044(2) Å, b = 11.2872(2) Å, c = 12.5276(5) Å, α = 66.694(2)°, β = 82.959(2)°, γ = 78.443(2)°, V = 699.52(5) Å3, Z = 2, M = 295.293 g mol−1, ρcalc = 1.4021 g cm−3, and ρmeas = 1.3935(66) g cm−3, which were obtained by means of the unit‐cell formula weight and a picnometric measurement, respectively. The goodness‐of‐fit and R‐factors were, respectively: χ2 = 1.746, RF2 = 1.69%, Rwp = 5.72%, and Rp = 4.37%. A weak nonclassical hydrogen bond involving the atoms N(3)H(23)⋯O(11) may be responsible for the greater stability of the polymorphic form A of mebendazole due to the strongest electronegativity of nitrogen. © 2009 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1734-1744, 2010