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

A new RuII 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 RuII 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-(trifluoromethyl)pyrazol-3-yl](2,2′-bipyrid-6-yl) ketone] in sequence. The respective charge-neutral OsII 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.