Molecular structure of hydrated complex of 1,4-dimethylpiperazine di-betaine with l-tartaric acid

1,4-Dimethylpiperazine di-betaine (DBPZ) forms a crystalline complex with l-tartaric acid (TA) and two and a half water molecules. The crystals are monoclinic, space group P21. The piperazine has a chair conformation with the methyl groups in the equatorial positions and the axial CH2COO substituents. One of the CH2COO group is protonated and forms with the neighboring DBPZ molecule the COOH⋯OOC hydrogen bond of the length 2.476(3) Å, which links them into a chain. The semi-tartrate anions, form a chain through the symmetrical, short COO⋯H⋯OOC hydrogen bond of 2.464(3) Å. The crystals have a layer structure, where hydrogen-bonded sheets of TA and water molecules are separated by the chains of DBPZ; no H-bonds between water and DBPZ are present. In the optimized molecules in the B3LYP/6-31G(d,p) approach, the tartaric acid interacts with the tartrate di-anions through the COOH⋯OOC hydrogen bonds of 2.506 Å, while the DBPZ has the same conformation as in the crystals. The FTIR spectrum of the solid complex is consistent with the X-ray results.