Syntheses, Spectral and Electrochemical Investigation of Coordination Complexes of Octakis(benzylthio)tetraazaporphyrinmaganese(II)

Abstract

Synthesis of [Mn(OBTTAP)], 1 and bichromophoric, di- and pentanuclear complexes with diimine-ruthenium(II) of the type [{Mn(OBTTAP)}{Ru(bpy)2}][PF6]2, 2, [{Mn(OBTTAP)}{Ru(phen)2}][PF6]2, 3, [{Mn(OBTTAP)}{RuCp(PPh3)}][PF6], 4, [{Mn(OBTTAP)}{Ru(bpy)2}4]- [PF6]8, 5, [{Mn(OBTTAP)}{Ru(phen)2}4][PF6]8, 6 and [{Mn(OBTTAP)}{RuCp(PPh3)}4][PF6]4, 7, (OBTTAP = octakis(benzylthio)tetraazaporphyrin) have been described. They were characterized using IR, 1H NMR, UV–visible, and mass spectral data. In the electronic absorption spectra the relative intensities and positions of the Soret and Q-bands, in the di- and pentanuclear complexes were observed shifted vis-à-vis that in the precursor complex 1. They all exhibit strong S2 emission. The emission intensity of the equimolar solutions of complexes 2, 3, 4 and 7 were found to be significantly higher than that of 1. The excitation-emission behaviors of the complexes are indicative of interchromophore energy transfer. Complexes 2–7 exhibited good electrode activity, particularly with multiple reversible redox waves in oxidative CV scans. The OBTTAP ring oxidations were observed as one or two reversible waves, depending upon number and nature of the peripheral metal units. Particularly, with four (bpy)2RuII units bonded to the [Mn(OBTTAP)] periphery, it was observed as two reversible, one electron oxidation waves at E 1/2 0.81 and 1.02 V vs. Ag/AgCl. Also the Ru(II)/Ru(III) oxidations were observed at significantly lower potential, in this complex, at E1/2 0.49 V vs Ag/AgCl due to weaker π-inteaction with dπ(S) orbitals.