Crystalline products of the reactions of piperazine (PZ) solutions with CO 2 sourced from the air and dry ice represent three carboxamides of piperazine, piperazinium carboxamide trihydrate (PZH + CO 2 − )•3H 2 O, piperazinium piperazine-4-carboxamide (PZH + )(PZCO 2 − ), and bis-(piperazinium) piperazine-1,4bis(carboxamide) trihydrate (PZH + ) 2 (PZ(CO 2 − ) 2 )•3H 2 O, whose crystal structures were revealed by single crystal X-ray diffraction studies. The interplay of hydrogen bonding affords the crystal stability of these hydrolytically labile piperazine carbamate derivatives which have not been observed in the solid state before. The crystal structure of piperazine monohydrate PZ•H 2 O is reported as well.

In an attempt to grow 8-hydroxyquinoline–acetaminophen co-crystals from equimolar amounts of conformers in a chloroform–ethanol solvent mixture at room temperature, the title compound, C9H7NO, was obtained. The molecule is planar, with the hydroxy H atom forming an intramolecular O—H...N hydrogen bond. In the crystal, molecules form centrosymmetric dimersviatwo O—H...N hydrogen bonds. Thus, the hydroxy H atoms are involved in bifurcated O—H...N hydrogen bonds, leading to the formation of a central planar four-membered N2H2ring. The dimers are bound by intermolecular π–π stacking [the shortest C...C distance is 3.2997 (17) Å] and C—H...π interactions into a three-dimensional framework. The crystal grown represents a new monoclinic polymorph in the space groupP21/n. The molecular structure of the present monoclinic polymorph is very similar to that of the orthorhombic polymorph (space groupFdd2) studied previously [Roychowdhuryet al.(1978).Acta Cryst.B34, 1047–1048; Banerjee & Saha (1986).Acta Cryst.C42, 1408–1411]. The structures of the two polymorphs are distinguished by the different geometries of the hydrogen-bonded dimers, which in the crystal of the orthorhombic polymorph possess twofold axis symmetry, with the central N2H2ring adopting a butterfly conformation.

Due to their unique ability to react directly and reversibly with CO2 to form carbamates, primary and secondary amines are widely acknowledged as a prospective means of CO2 capture and solid storage. Piperazine has become a prime focus of amine-based research for post-combustion capture. The kinetics of piperazine's reversible reactivity with CO2 have been vastly described in literature. A series of experiments was carried out to determine the effectiveness of certain amines in CO2 capture.Different conditions of reactions of amines with CO2 were utilized to obtain crystalline products. The following amines were used: anhydrous piperazine and its hexahydrate, 2,6 dimethylpiperazine, 4-piperidone monohydrate hydrochloride, piperidine and 4methylpiperidine. Saturated aqueous amine solutions were prepared, as well as a 1:1 water:ethanol solutions. CO2 was added to these solutions sourcing from both solid (dry ice) and gas. Time intervals and rates of CO2 distribution were varied to discover if it affected the structure of final products. In addition to saturated solutions, pure piperidine, dimethylpiperizine, anhydrous piperazine, and its hexahydrate were allowed to react with atmospheric CO2. Crystalline products obtained from this spontaneous reactions were analyzed.Single crystal X-Ray analysis revealed the formation of mono-and dicarbamate derivatives that have been previously observed, with the exception of a monohydrate product. Cation-anion interactions and hydrogen bonding patterns in the resulting carbamates are discussed.

Recently cocrystallization became a popular tool for crystal engineering that allows, for instance, improving properties of pharmaceutical materials, creating new materials for nonlinear optical applications and solar cell technologies. To attract students to crystallographic studies we carried out project that included crystal growth of two series of cocrystals with acetaminophen and with dicarbonic glutaric acid. We attempted cocrystallization of acetaminophen with more than ten different coformers which gave no cocrystals or salts. However, as a result of cocrystallization we obtained new polymorph modification of hydroxyquinoline. On the contrary, cocrystallization of glutaric acid with basic organic compounds gave several new salts. Interesting examples among them are systems of glutaric acid with 2-pyridinamine and with 6-methyl-2-pyridinamine. In spite of the presence of the same substituents that are prone to H-bond formation, cocrystals have different H-bonding systems and even different molecular conformation of glutaric acid. Details of physical properties, such as spectral characteristics and melting points, of obtained multicomponent materials are discussed.