Synthesis, spectroscopic and hydrogen storage studies of mono or bimercury(II) mixed ligand complexes of amines with 2-cyanoamino thiophenolate ligand

Abstract

Organic heterocyclic compounds play a significant role in coordination chemistry due to their ability to act as donor atoms for coordinating with various metal or metal ions. In this study, particular attention was given to the conversion of the 2-aminobenzothiazole ligand into 2-cyanoaminothiophenolate (LH) through a ring-breaking reaction. This transformation was achieved by reacting 2-aminobenzothiazole with phenyl mercury(II) acetate in the presence of sodium hydroxide, resulting in the formation of the complex [pHHg(LH)]n. During this process, mono-deprotonation of 2-aminobenzothiazole occurred, accompanied by facial carbon-sulfur bond breaking. This complex was used as a synthon to prepare four new mononuclear and binuclear complexes, which were [pHHg(LH)(apmy)2] (apmy= 2-aminopyrimidine) and [PhHg(LH)(bipy)] and [pHHg(LH)(μ-Cl)2Hg(bipy)] and [pHHg(LH)(μ-Cl)2Hg(phen)]. The prepared complexes were characterized using melting point, elemental analysis, FTIR, 1HNMR and 13CNMR. The results showed that the 2-cyanoamino thiophenolate ligand exhibited a monodentate behavior across the thiol sulfur atom, while the nitrile group remained free. The complex [pHHg(LH)(μ-Cl)2Hg(phen)] was used to study its ability to store hydrogen at different temperatures in order to study the thermodynamic parameters (enthalpy and entropy). The study proved that the highest stored value was 1.92 wt.% H2. It was noted that this ratio can be stored at lower pressures as the temperature decreases, proving that the storage is of a physical type with the value of R2= 0.92602 for the Van't Hof plot. The enthalpy value was 0.1131118 (kJ/(mol H2) while the entropy value was 0.60649754 (J/mol H2. K).