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

Abstract

Water photolysis to molecular hydrogen and oxygen is one of the most promising chemical reactions for a sustainable hydrogen generation. The search for catalysts for this process is an important research area; some of the most suggested catalysts are manganese complexes. However, several studies propose the use of the complex: tris(bipyridine)ruthenium(II) chloride to be used as catalyst in artificial photosynthesis. In spite of this, the conferred properties by the 2,2′-bipyridyl ligand, in manganese or ruthenium 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 2,2′-bipyridyl or 1,10-phenanthroline, a spectrophotometric study of the speciation in methanol of these systems at 298K, was performed. The formation constants obtained for the manganese(II)-2, 2′-bipyridyl system are: log β110 = 7.81 and log β120 = 14.68; for the manganese(II)-1,10-phenanthroline system are log β110 = 6.94 and log β120 = 12.86. These results were obtained by refining the experimental spectrophotometric data using the HypSpec software. In addition, a brief discussion of the comparison of the calculated individual electronic spectra of the complexes reported in this work with the spectrum of the tris(bipyridine)ruthenium(II) chloride and the manganese-calcium oxygen-evolving complex of photosystem II is presented.