Comparative Electrochemistry, Electronic Absorption Spectroscopy and Spectroelectrochemistry of the Monometallic Ruthenium Polypyridyl Complexes, [Ru(Bpy)(Dpb)2](Pf6)2, [Ru(Bpy)2(Dpb)](Pf6)2, [Ru(Bpy)2(Dpq)](Pf6)2, [Ru(Bpy)(Dpq)2](Pf6)2
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The novel compound [Ru(bpy)(dpb)â (PFâ )â was synthesized, in a manner similar to the literature synthesis of [Ru(bpy)(dpq)â (PFâ )â . For the sake of completeness, the related analogs, [Ru(bpy)â (dpb)](PFâ )â , [Ru(bpy)â (dpq)](PFâ )â and [Ru(bpy)(dpq)â ](PFâ )â were also synthesized. Alumina adsorption chromatography was used for purification purposes. Liquid secondary ion mass spectroscopy was used to confirm identity of compounds. The new compound contained 1% electroactive impurity as determined by OSWV. Spectroelectrochemical studies were conducted with both a bulk H-cell and a ~0.2 mm pathlength, optically transparent thin layer electrode (OTTLE) cell. High reversibility (a 99%) is possible with dilute solutions (ca 10â »â ´ M) and the OTTLE cell as compared to ca 50% with the H-cell. Spectroelectrochemical data supported the following electronic transitions for the new compound [Ru(bpy)(dpb)â ](PFâ )â : (1) the Ru (dÏ ) â dpb MLCT at 552 nm, (2) a d â d at 242 nm, a bpy Ï â Ï * at 285 nm. (3) The location of the Ru (dÏ ) â bpy MLCT peak is obscured by shoulders from 390-420 nm. (4) The strong peak at 316 nm may be dpb Ï â Ï â *, the location of the lower energy intraligand dpb Ï â Ï â * is uncertain. Upon oxidation of the metal center, no LMCT was observed within the UV-VIS range. This is in direct contrast to the results of Gordon et al. This author hypothesizes that their LMCT found in the visible region was actually the result of incomplete electrochemical conversion and that a LMCT should be seen in the NIR. The spectroelectrochemical properties of [Ru(bpy)(dpq)â ](PFâ )â were also presented for the first time. These results indicated that the 256 nm transition was d â d and not bpy Ï â Ï â * as suggested by Rillema et al.
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