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), C(13)H(28)N(4)O(2), designated alpha and beta, 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 alpha form was first crystallized from acetonitrile solution, while the beta form was obtained by recrystallization of the alpha phase from diethyl ether. The alpha form crystallizes in the triclinic system (space group P-1), with one molecule in the asymmetric unit, while the crystal of the beta form is monoclinic (space group P2(1)/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.