The Crystal and Molecular Structure of Piperazinium Terephthalate, (H2NC4H8NH2)2+(O2C·C6H4·CO2)2−

Piperazinium terephthalate has been prepared and examined by X-ray analysis. The compound crystallizes in the monoclinic space group P21⁄c with two formula units in a unit cell. The cell dimensions are: a=9.45, b=8.30, c=8.33 Å, and β=117.3°. The structure was determined by the Patterson method from the data collected with CuKα radiation on Weissenberg photographs, and refined by the block-diagonal least-squares method with anisotropic temperature factors for non-hydrogen atoms and fixed isotropic ones for hydrogen atoms. The final R value is 0.108 for 941 non-zero reflections. Acid and base moieties occupy the positions of center of symmetry in the cell. Two N+−H…O− hydrogen bonds (2.612 and 2.737 Å) link a nitrogen atom of piperazine with two carboxyl oxygens of the acids related by c glide plane to form a three-dimensional hydrogen bond network, in which each oxygen atom accepts one hydrogen bond. The coordination around the nitrogen atom is nearly tetrahedral. The piperazine ring takes a chair form. The twisting angle between the carboxyl group and the benzene ring plane is 17.3°.