How to Modulate the Absorption Properties of a Novel Iron Bipyridyl Complex by Introducing Peripheral Ruthenium Ammines

MECCHIA ORTIZ, JUAN HUGO; KATZ, NÉSTOR E.

Singapur

Congreso; 41th International Conference on Coordination Chemistry; 2014

IUPAC

Iron bipyridyl complexes are relevant in such fields such as inexpensive dye-sensitized solar cells or non-linear optical materials. In this work, we report the synthesis and spectroscopic and electrochemical properties of PF6- salts of novel mono-, di- and tetranuclear complexes of formulae: [Fe(Mebpy-CN)3]2+ (1), [(Mebpy-CN)2Fe(Mebpy-CN)Ru(NH3)5]4+ (2) and {[Fe(Mebpy-CN)3](Ru(NH3)5)3}8+ (3) respectively, with Mebpy-CN = 4-methyl-2,2'-bipyridine-4'-carbonitrile. By oxidizing (2) and (3) with Br2 in CH3CN solutions, the new mixed-valent species [(Mebpy-CN)2FeII(Mebpy-CN)RuIII(NH3)5]5+ (4) and {[FeII(Mebpy-CN)3](RuIII(NH3)5)3}11+ (5) could be obtained. All the complexes exhibit quasireversible oxidations for the metallic centers. A slight increase of the oxidation potential of the metallic centers is detected along the series. As shown in Figure 1, MLCT [dπ(Fe) → π* (Mebpy-CN)] bands appear at λmax = 546 nm (εmax = 0.9 x 104 M-1cm-1) for (1), 573 nm (εmax = 2.0 x 104 M-1cm-1) for (2) and 581 nm (εmax = 3.8 x 104 M-1cm-1) for (3), in CH3CN. The shift to lower energies and the dramatic increase in intensity in going from (1) to (3) is due to the electron accepting properties of the peripheral ruthenium ammines added in sequence. The corresponding MLCT [dπ(Ru) → π* (Mebpy-CN)] bands appear at λmax ca. 500 nm and increase in intensity in going from (1) to (3). [FeII → RuIII] MMCT bands appear in (4) and (5) at λmax = 850 nm, with the intensity increased in the latter complex by a factor of 4. We conclude that introducing ruthenium ammines one at a time in the periphery of a new iron bypyridyl complex can modulate the absorption coefficients in the UV-visible region when using Ru(II) or in the near-IR region when using Ru(III).