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Reports on the spectroscopy, electrochemistry and linkage isomerization in a family of [Ru(tpy)(L2)(dmso)[sup Z+] complexes. Importance of ancillary ligands in photochromic ruthenium-dmso complexes; Role of electron transfer in isomerization.

Discusses the spectroscopy and electrochemistry of halo-ruthenium(sulfoxide) complexes. Structure of mer[RuCl3(dimethylsulfoxide)(tmen0]; Exhibition of two reversible electron waves by the acetonitrile mer [RuCl3(dmso)(tmen)] solution; Indication of a pi-back-bonding between Ru(III) or Ru(II) and dmso in the solution.

The photochromic compounds trans- and cis-[Ru(tpy)(Mepic)(dmso)](OSO2CF3) (2 and 3, respectively; tpy is 2,2′: 6′,2″-terpyridine; Mepic is 6-methyl-2-pyridinecarboxylate; dmso is dimethyl sulfoxide) and cis-[Ru(tpy)(Brpic)(dmso)]- (PF6) (4; Brpic is 6-bromo-2-pyridinecarboxylate) were prepared and characterized by single-crystal X-ray crystallography, electrochemistry, NMR, IR, and UV-vis spectroscopy. The geometry labels refer to the relationship between the carboxylate oxygen of the picolinate ligand and dmso. Electrochemical studies reveal that only the trans isomer shows S-to-O isomerization following oxidation of Ru(ll) and O-to-S isomerization following reduction of Ru(lll). The cis isomers of both complexes feature reversible one-electron Ru(lll/ll) couples. All complexes undergo phototriggered S-to-O isomerization following MLCT (metal-to-ligand charge transfer) excitation with quantum yields (ΦS→O) of 0.79 (2), 0.011 (3), and 0.014 (4). The methyl group in 2 promotes isomerization by hindering rotation of the dmso ligand about the Ru-S bond. Computational results support this role for the methyl group. Relative energy calculations show that the barrier to rotation is approximately 8 kcal mol-1. These results suggest that rotation is an important vibration for isomerization in photochromic ruthenium-dmso complexes. [ABSTRACT FROM AUTHOR]

Compounds of the type [Ru(tpy)(L2)(dmso))2+ (tpy is 2,2′:6′,2″-terpyridine; L2 can be 2,2′-bipyridine (bpy), N,N,N′,N′-tetramethylethylenediamine (tmen), 2-pyridine carboxylate (pic), acetylacetonate (acac), malonate (mal), or oxalate (ox)) have been studied by X-ray crystallography, electrochemistry, NMR, IR, and UV-vis spectroscopy. When L2 is bpy, tmen, or pic, the dmso ligand can be intramolecularly isomerized either electrochemically or photochemically. lsomerization is not observed when L2 is acac, mal, or ox. Isomerization results in a drastic change in the absorption spectrum, as well as in the voltammetry. Absorption maxima shift by 3470 (419-490 nm), 4775 (421-527 nm), and 4440 cm-1 (429-530 nm) for the bpy, pic, and tmen complexes, respectively. Reduction potentials for S-bonded and O-bonded complexes differ by 0.57, 0.75, and 0.62 V for the bpy, pic, and tmen complexes, respectively. Quantum yields of isomerization (ϕS→O) were determined for the bpy (0.024 ± 1), pic (0.25 ± 1), and tmen (0.007 ± 1) complexes. In comparison of these data to photosubstitution quantum yields, it appears that the isomerization mechanism does not involve the ligand field states. This result is surprising given the importance of these states in the photochemistry of ruthenium and osmium polypyridine complexes. These results and details of the mechanism are discussed. [ABSTRACT FROM AUTHOR]

We report the structure, electrochemistry, and isomerization kinetics for [Ru(bpy)(biq)(OSO)](PF6), where bpy is 2,2′-bipyridine, biq is 2,2′-biquinoline, and OSO is 2-methylsulfinylbenzoate. UV-visible and infrared data are suggestive of intramolecular S→O and O→S isomerization of the sulfoxide. Cyclic voltammetry reveals evidence for isomerization triggered by oxidation and reduction. Of particular note is the variation of the S→O isomerization rate constant in different solvents. The rates were found to be 3.2 (±0.4) s-1 in propylene carbonate, 0.80 (±0.03) s-1 in acetonitrile, and 0.26 (±0.01) s-1 in dichloromethane. [ABSTRACT FROM AUTHOR]

The complexes [Ru(bpy)2(OS)](PF6) and [Ru(bpy)2(OSO)](PF6), where bpy is 2,2'-bipyridine, OS is 2-methylthio-benzoate, and OSO is 2-methylsulfinylbenzoate, have been studied. The electrochemical and photochemical reactivity of [Ru(bpy)2(OSO)]+ is consistent with an isomerization of the bound sulfoxide from S-bonded (S-) to O-bonded (O-) following irradiation or electrochemical oxidation. Charge transfer excitation of [Ru(bpy)2(OSO)]+ in MeOH results in the appearance of two new metal-to-ligand charge transfer (MLCT) maxima at 355 and 496 nm, while the peak at 396 nm diminishes in intensity. The isomerization is reversible at room temperature in alcohol or propylene carbonate solution. In the absence of light, solutions of O-[Ru(bpy)2(OSO)+ revert to S-[Ru(bpy)2(OSO)]+. Kinetic analysis reveals a biexponential decay with rate constants of 5.66(3) x 10-4 s-1 and 3.1(1) x 10-5 s-1. Cyclic voltammograms of S-[Ru(bpy)2(OSO)+ are consistent with electron-transfer-triggered isomerization of the sulfoxide. Analysis of these voltammograms reveal ESo' = 0.86 V and EOo' = 0.49 V versus Ag/Ag+ for the S- and O-bonded Ru3+/2+ couples, respectively, in propylene carbonate. We found ks-o = 0.090(15) s-1 in propylene carbonate and ks-o = 0.11(3) s-1 in acetonitrile on RuIII, which is considerably slower than has been reported for other sulfoxide isometizations on ruthenium polypyridyl complexes following oxidation. The photoisomerization quantum yield (Φs-o = 0.45, methanol) is quite large, indicating a rapid excited state isomerization rate constant. The kinetic trace at 500 nm is monoexponential with τ = 150 ps, which is assigned to the excited S-O isomerization rate. There is no spectroscopic or kinetic evidence for an O-bonded 3MLCT excited state in the spectral evolution of S-[Ru(bpy)2(OSO)]+ to O-[Ru(bpy)2(OSO)]+. Thus, isometization occurs nonadiabatically from an S-bonded (or η2-sulfoxide) 3MLCT excited state to an O-bonded ground state. Density functional theory calculations support the assigned spectroscopy and provide insight into ruthenium ligand bonding. [ABSTRACT FROM AUTHOR]