Synthesis and structure of trans-2,5-di-methyl-piperazine-1,4-diium di-hydrogen diphosphate.

In the title salt, C6H16N2 2+ ·H2P2O7 2-, the complete dication is generated by a crystallographic centre of symmetry with the methyl groups in equatorial orientations. The complete dianion is generated by a crystallographic twofold axis with the central O atom lying on the axis: the P-O-P bond angle is 135.50 (12)°. In the crystal, the di-hydrogen diphosphate anions are linked by O-H⋯O hydrogen bonds, generating (001) layers. The organic cations bond to the inorganic layers by way of N-H⋯O and C-H⋯O hydrogen bonds. A Hirshfeld surface analysis shows that the most important contributions for the crystal packing are from O⋯H/H⋯O (60.5%) and H⋯H (39.4%) contacts.