Fine Tuning of MLCT States in New Mononuclear Complexes of Ruthenium (II) Containing Tris(1-pyrazolyl)methane, 2,2'-Bipyridine and Aromatic Nitrogen Heterocycles

KATZ, NÉSTOR E; ROMERO, ISABEL; LLOBET, ANTONI; PARELLA, TEODOR; BENET-BUCHHOLZ, JORDI

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

Wiley-VCH

Lugar: Weinheim; Año: 2005 p. 272 - 277

1434-1948

The syntheses of new mononuclear ruthenium (II) complexes of the type: [Ru(tpm)(bpy)(L)](PF6)2, with tpm = tris(1-pyrazolyl)methane, bpy = 2,2´-bipyridine, and L = pz (pyrazine), 1, 4,4´-bpy (4,4´-bipyridine), 2, and BPE (trans-1,2-bis(4-pyridyl)ethylene), 3, are described, together with their spectroscopic, electrochemical and photophysical properties. A complete assignment of NMR resonances of the three species could be made in CD3CN by bidimensional techniques. A fine tuning of the energies of MLCT (metal-to-ligand charge transfer) states in these complexes is disclosed when comparing, in CH3CN, their values of the maximum absorption wavelengths for the most intense visible bands (lmax) and their redox potentials for the Ru(III)/Ru(II) couples; this effect, relevant to the design of efficient photocatalysts, can be attributed to a decreasing order of dp(Ru)® p*(2,2´-bpy) backbonding when decreasing the distance between both N atoms in the aromatic nitrogen heterocycle L that acts in a monodentate manner. Only the species with L = BPE emits at room temperature, pointing to the conclusion that MLCT excited states in this series become higher in energy than dd excited states when the value of lmax is lower than 400 nm. These species are also useful building blocks for new dinuclear mixed-valent complexes.