N,N′-Dimethylpiperazine mono-betaine complex with two molecules of 3-iodobenzoic acid and water studied by X-ray diffraction, DFT, FTIR and NMR methods

N,N′-Dimethylpiperazine mono-betaine (N-carboxymethyl-N,N′-dimethylpiperazinium inner salt, MBPZ) forms a crystalline complex with two molecules of 3-iodobenzoic acid (3IBA). The complex crystallizes as a monohydrate, MBPZ(3IBA)2H2O. The complex has been characterized by X-ray diffraction and FTIR, Raman, 1H and 13C NMR spectroscopies. The crystals are monoclinic, space group P21/c, with a = 6.7810(17), b = 38.391(4), c = 10.0542(16) Å, β = 90.024(18)°. The piperazinium ring has a chair conformation with the N+CH2COO− substituent in the axial and both methyl groups in the equatorial positions. The 3IBA molecules interact with the carboxylate group of N+CH2COO− and N′ atom through the O–H···O and O–H···N hydrogen bonds of the lengths 2.550 and 2.695 Å. The water molecules link MBPZ(3IBA)2 complexes by the O–H···OOCCH2N+ hydrogen bonds of 2.850 and 2.793 Å into infinite chains. The MBPZ(3XBA)2H2O (X = I, Br, Cl), MBPZ(3IBA)2 complexes and MBPZ have been analyzed by the B3LYP/MidiX level of theory. The conformers with the axial CH2COO− substituent have lower energies than these with the equatorial CH2COO− one. The bands at 3433, 2790, 2450, 1915 cm−1 assigned to the ν(OH) vibration of the various hydrogen bonds, and two bands attributed to the ν(CO) (1680 cm−1) and νas(COO) (1660 cm−1) vibrations in the FTIR spectrum confirm the structure of the title complex. The 1H–13C HMBC spectrum has been analyzed in order to assign the carbon-13 chemical shifts.