Powder X‐ray studies of meso‐hexamethyl propylene amine oxime (meso‐HMPAO) in two different phases

Two different forms of meso‐3,3′‐2,2‐dimethylpropane‐1,3‐diylbis(azanediyl)]dibutan‐2‐one dioxime, commonly called meso‐hexamethyl propylene amine oxime (HMPAO), C₁₃H₂₈N₄O₂, designated α and β, were isolated by fractional crystallization and their crystal structures were determined by powder X‐ray diffraction using the direct‐space method with the parallel tempering algorithm. The α form was first crystallized from acetonitrile solution, while the β form was obtained by recrystallization of the α phase from diethyl ether. The α form crystallizes in the triclinic system (space group P), with one molecule in the asymmetric unit, while the crystal of the β form is monoclinic (space group P2₁/n), with one molecule in the asymmetric unit. In both phases, the molecules have similar conformations and RS/EE geometric isomerism. The crystal packing of the two phases is dominated by intermolecular hydrogen‐bonding interactions between the two O—H oxime groups of an individual molecule and the amine N atoms of two different adjacent molecules, which lead to segregation of extended poly(meso‐HMPAO) one‐dimensional chains along the c direction. The structures of the two phases are primarily different due to the different orientations of the molecules in the chains.