New Series of Ruthenium(II) and Osmium(II) Complexes Showing Solid-State Phosphorescence in Far-Visible and Near-Infrared

A new Ru^II complex, [Ru(fpbpymH)2]Cl₂ (1), in which fpbpymH = [5-(trifluoromethyl)pyrazol-3-yl](2,2'-bipyrid-6-yl)methane, was prepared by the treatment of [Ru(DMSO)₄Cl₂] with 2 equiv of the terdentate chelate fpbpymH in refluxing ethanol. A single-crystal X-ray diffraction study of 1 revealed a distorted octahedral Ru^II framework, showing strong N-H- ... Cl hydrogen bonding between the fpbpymH ligand and Cl anions. In the presence of Na₂CO₃, the methylene linkers of chelates in 1 underwent stepwise oxygenation, forming the charge-neutral complexes [Ru(fpbpym)(fpbpyk)] (2) and [Ru(fpbpyk)₂] (3) [fpbpykH = [5-(trtfluoromethyl)pyrazol-3-yG(2,2'-bipyrid-6-yl) ketone] in sequence. The respective charge-neutral Os^II complex [Os(fpbpyk)₂] (4) was also isolated by the treatment of OsCl₃·3H₂O with 2 equiv of the terdentate chelate fpbpymH. Electrochemical analysis indicated that the introduction of the electron-withdrawing ketone group in 2-4 increased the metal-based oxidation potential in sequence. For the photophysical properties, complexes 1-4 are essentially nonluminescent in solution (e.g., CH₂Cl₂ or MeOH) at room temperature, but all exhibit 600-1100 nm phosphorescence with moderate intensity for the powdery, solid sample at room temperature. The trend in terms of the emission peak wavelength of 1 (666 nm) < 3 (795 nm) < 2 (810 nm) < 4 (994 nm) among titled complexes is in agreement with the corresponding onset of absorption spectra as well as the time-dependent density functional theory calculation of 1 < 3 < 2 < 4.