Structural and spectroscopic studies of the 1:1 complex of meso-tartaric acid with 1,4-dimethylpiperazine di-betaine

Crystal structure of the 1:1 complex of 1,4-dimethylpiperazine di-betaine (1,4-dimethyl-1,4-dicarboxymethylpiperazinium, inner salt, DBPZ) with meso-tartaric acid (meso-TA) has been determined by X-ray diffraction. The crystals are triclinic, space group P  1¯. meso-TA and DBPZ are linked by the COOH···OOC hydrogen bonds of 2.536(2) Å into infinite chains, which are interconnected through the OH···OC hydrogen bonds of 2.693(2) Å. The molecules of DBPZ·meso-TA complex are located on two independent inversion centers, but the crystal is nearly isostructural with the chiral complex of l-tartaric acid [(+)TA] with DBPZ (triclinic, space group P1). In both these structures the piperazine ring has a chair conformation with the axial CH3 groups and the equatorial CH2COO− substituents. The solid-state FTIR spectrum is consistent with the X-ray results. In the structure of the isolated DBPZ·meso-TA complex optimized at the B3LYP/6-31G(d,p) level of theory, the hydrogen-bonded aggregates of DBPZ and meso-TA molecules (the O···O distance of 2.442 Å) are folded.