Complex formation equilibria of 2,20-bipyridyl and 1, 10-phenanthroline with manganese(II) in methanol


Water photolysis to molecular hydrogen and oxygen is one of the most promising chemical reactions for a sustainable hydrogengeneration. The search for catalysts for this process is an important research area; some of the most suggested catalysts aremanganese complexes. However, several studies propose the use of the complex: tris(bipyridine)ruthenium(II) chloride to be usedas catalyst in artificial photosynthesis. In spite of this, the conferred properties by the 2,20-bipyridyl ligand, in manganese orruthenium complexes has not yet been discussed extensively.In this work, in order to obtain more insight of the behavior of manganese(II) with several ligands such as 2,20-bipyridyl or 1,10-phenanthroline, a spectrophotometric study of the speciation in methanol of these systems at 298 K, was performed. The formationconstants obtained for the manganese(II)-2, 20-bipyridyl system are: log b110 ¼ 7.81 and log b120 ¼ 14.68; for the manganese(II)-1,10-phenanthroline system are log b110 ¼ 6.94 and log b120 ¼ 12.86. These results were obtained by refining the experimentalspectrophotometric data using the HypSpec software. In addition, a brief discussion of the comparison of the calculated individualelectronic spectra of the complexes reported in this work with the spectrum of the tris(bipyridine)ruthenium(II) chloride and themanganese-calcium oxygen-evolving complex of photosystem II is presented.