Crystal and molecular structure of Michler’s ketone as a pure phase

Abstract

The pure phase crystals of Michler’s ketone, [4-(CH₃)₂NC₆H₄]₂CO, are reported herein as monoclinic in the space group P2₁/c with Z’ = 2 by single-crystal X-ray diffraction. The data collection of the title compound proved quite difficult, which could explain why the structure has not been reported previously. The crystallographically independent molecules in the asymmetric unit differ by dihedral angles of 24.60/30.34° and 25.25/27.20° between the essentially planar 4-dimethylaminophenyl (DMAP) rings and the central C₂C=O plane of the ketone and dihedral angles of 52.14 and 47.41°, respectively, between the DMAP planes. A DMAP ring of each molecule overlaps in the lattice with a methyl ring that overlays the ring centroid of the opposite number (C_Me-C_g distances of 3.452 and 3.505 Å), describing sets of trifurcated C_Ar-acceptor hydrogen bond interactions (HBIs). The trifurcated HBIs possess H∙∙∙C_Ar distances of 2.90, 2.75, and 2.86 Å; C_Me∙∙∙C_ar distances of 3.554(5), 3.798(5) and 3.881(5) Å; and ÐC_Me-H∙∙∙C_Ar of 115.0, 121.3 and 167.7°, respectively. Stabilization of the asymmetric unit in the title compound is further achieved by supramolecular synthons such as C_Me-H∙∙∙C_Ar (2.831 Å), C_Ar-H∙∙∙O (2.561 Å) and C_Ar-H∙∙∙H-C_Ar (2.290 Å) and coulombic C_Me-Ocontact (3.209 Å). The structures of the two independent molecules in the asymmetric unit of the title compound were compared with the same molecule as found in the following co-crystals, adducts or salts: a halogen-bonded adduct with 1,4-diiodotetrafluorobenzene; a hydrogen-bonded adduct with a fluorinated phenol; a coordination complex between the ketone and a trimeric mercury acceptor; and two salts from protonation or methylation at one of the amino nitrogen atoms.