Molecular structure of 1:1 complex of 1,4-dimethylpiperazine di-betaine with l-tartaric acid studied by X-ray diffraction, FTIR, Raman and NMR spectroscopy and DFT calculations

Crystal structure of the 1:1 complex of 1,4-dimethylpiperazine di-betaine (1,4-dicarboxymethyl-1,4-dimethylpiperazinium inner salt, DBPZ) with l-tartaric acid (TA) has been determined by X-ray diffraction. The crystals are triclinic, space group P1. TA and DBPZ are linked by two asymmetric COOH···OOC hydrogen bonds of 2.485(3) and 2.566(3) Å into chains. The piperazine ring has a chair conformation with the methyl groups in the axial positions and the CH2COO− substituents in the equatorial ones. In the theoretically optimized structure of isolated DBPZ·TA at the B3LYP/6-31G(d,p) level of theory the non-linear complex, with DBPZ in the same conformation as in the crystal, is formed. The 1H and 13C magnetic isotropic shielding tensors have been analyzed in order to confirm the CH···O contacts, which stabilize the optimized structure of DBPZ·TA. The FTIR spectrum of the solid complex is consistent with the X-ray results.