Orthorhombic Polymorphs of 1-Phenyl-3-(3-Hydroxyphenyl)-2-Propen-1-One

Abstract  

Chalcones, 1,3-diphenyl-2-propene-1-ones, exist naturally and synthetically, and are characterized by the linkage of two aromatic rings joining a three carbon α-β-unsaturated carbonyl entity. We report the observation of two new polymorphs of a hydroxy chalcone, C₆H₅–CO–CH=CH–C₆H₄ (m-OH), identified as a result of a Claisen–Schmidt synthesis and manual screening technique. One polymorph of this compound has been reported previously and exists in the monoclinic system, space group P2/n, with unit cell parameters a = 13.295(6) ?, b = 5.659(2) ?, c = 16.144(8) ?, β = 109.73(5)°, V = 1143.3(9) ?³, and Z = 4. Two crystalline forms (II and III) reported herein, are polymorphs of the reported monoclinic form (I). Form II exists in the orthorhombic system, space group Pca2₁, with unit cell constants a = 11.631 (2) ?, b = 13.163 (3) ?, c = 7.3977 (14) ?, V = 1132.6 (4) ?³, and Z = 4. Form III also crystallizes in the orthorhombic system, however in space group Pbca, with unit cell parameters a = 11.8100(8) ?, b = 7.4075(5) ?, c = 25.8729(19) ?, V = 2263.4(3) ?³, and Z = 8. Variations in the hydrogen bonding connectivity help to distinguish these two forms from the monoclinic, whereas crystal packing differentiates the two orthorhombic forms. The conformation of the C=C (C2–C3) is E for both orthorhombic forms.