Synthesis, spectroscopic characterization and structural studies of a new proton transfer (H-bonded) complex of o-phenylenediamine with l-tartaric acid

• A proton transfer complex is synthesized and characterized by spectral techniques.
• Bonding modes and structural information are ascertained from crystallographic studies.
• Single-crystal X-ray studies confirmed the H-bonded network.
• Thermal analysis (TGA–DTA) was also used to confirm the thermal fragmentation and the stability of the CT complex.
• Benesi–Hildebrand equation was used to determine KCT, εCT, and ECT of the CT complex.

A proton transfer or H-bonded (CT) complex of o-phenylenediamine (OPD) as donor with l-tartaric acid (TART) as acceptor was synthesized and characterized by spectral techniques such as FTIR, 1H NMR, elemental analysis, TGA–TDA, X-ray crystallography and spectrophotometric studies. The structural investigations exhibit that the cation [OPD+] and anion [TART−] are linked together through strong N+–H⋯O− type hydrogen bonds due to transfer of proton from acceptor to donor. Formed H-bonded complex exhibits well resolved proton transfer bands in the regions where neither donor nor acceptor has any absorption. The stoichiometry of the H-bonded complex (HBC) was found to be 1:1, determined by straight line methods. Spectrophotometric studies have been performed at room temperature and Benesi–Hildebrand equation was used to determine formation constant (KCT), molar extinction coefficient (εCT) and also transition energy (ECT) of the H-bonded complex. Spectrophotomeric and crystallographic studies have ascertained the formation of 1:1 H-bonded complex. Thermal analysis (TGA–DTA) was also used to confirm the thermal fragmentation and the stability of the synthesized H-bonded complex.