STRUCTURAL-CHEMICAL TRANSFORMATIONS DURING ORGANIC SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS - CRYSTAL-STRUCTURE OF PIPERAZINE MALONATE AND ITS CRYSTAL HYDRATE

An organic salt, piperazine malonate, was prepared by self-propagating high-temperature synthesis (SHS) in a solid-phase piperazine-malonic acid (P-M) system. Triclinic crystals of piperazine malonate (PM) hydr ate (1) were isolated from an aqueous solution. Monoclinic crystals of anhydrous piperazine malonate (2) were isolated from a solution in DM SO. Crystals 1 and 2 were studied by X-ray structural analysis. Struct ures 1 and 2 consist of centrosymmetrical piperazinium cations, which are linked to anions of malonic acid through N-H ... O hydrogen bonds. In structure 1, the anion is asymmetrical. The angle between the plan es of the carboxyl groups and the plane of the CH2 groups are 29.2 deg rees and 99.9 degrees. In structure 2, the anion is located on a twofo ld axis, and the corresponding angles are 81.5 degrees. The N ... O di stances are in the range of 2.691(4)-2.838(5) Angstrom.