Stability of Manganese(II)–Pyrazine, –Quinoxaline or –Phenazine Complexes and Their Potential as Carbonate Sequestration Agents

Carbonate sequestration technology is a complement of CO(2) sequestration technology, which might assure its long-term viability. In this work, in order to explore the interactions between Mn(2+) ion with several ligands and carbonate ion, we reported a spectrophotometric equilibrium study of complexes of Mn(2+) with pyrazine, quinoxaline or phenazine and its carbonate species at 298 K. For the complexes of manganese(II)–pyrazine, manganese(II)–quinoxaline and manganese(II)–phenazine, the formation constants obtained were log β(110) = 4.6 ± 0.1, log β(110) = 5.9 ± 0.1 and log β(110) = 6.0 ± 0.1, respectively. The formation constants for the carbonated species manganese(II)–carbonate, manganese(II)–pyrazine–carbonate, manganese(II)–quinoxaline–carbonate and manganese(II)–phenazine–carbonate complexes were log β(110) = 5.1 ± 0.1, log β(110) = 9.8 ± 0.1, log β(110) = 11.7 ± 0.1 and log β(110) = 12.7 ± 0.1, respectively. Finally, the individual calculated electronic spectra and its distribution diagram of these species are also reported. The use of N-donor ligand with π-electron-attracting activity in a manganese(II) complex might increase its interaction with carbonate ions.