Homoleptic tris(dithiolene) and tetrakis(dithiolene) complexes of uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4](infinity) (1). The red crystals of 1 are composed of infinite zigzag chains in which Na2(micro-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties; the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6), only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3].2py (2.2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3) were also obtained along with orange crystals of 2.2py. All the tris(dithiolene) compounds exhibit large folding of the dddt ligand and significant interaction between the C=C double bond and the metal center.     

Generation of bis(dithiolene)dioxomolybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media

Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum(iv) (Mo(IV)OL(x)) complexes is studied as a model of oxidative-half reaction of arsenite oxidase molybdenum enzymes. The reactions are revealed to involve proton-coupled electron transfer. Electrochemical oxidation of Mo(IV)OL(x) yields the corresponding bis(dithiolene)dioxomolybdenum(vi) complexes in basic solution, where the conversion of Mo(IV)OL(dmed) supported by a smaller electron donating dithiolene ligand (1,2-dicarbomethoxyethylene-1,2-dithiolate, L(dmed)) to Mo(VI)O(2)L(dmed) is faster than that of Mo(IV)OL(bdt) with a larger electron donating dithiolene ligand (1,2-benzenedithiolate, L(bdt)) under the same conditions. Titration experiments for the electrochemical oxidation reveal that the reaction involves two-electron oxidation and two equivalents of OH(-) consumption per Mo(IV)OL(x). In the conversion process of Mo(IV)OL(x) to Mo(VI)O(2)L(x), the five-coordinate bis(dithiolene)monooxomolybdenum(v) complex (Mo(V)OL(x)) being a one-electron oxidized species of Mo(IV)OL(x) is suggested to react with OH(-). Mo(V)OL(x) reacts with OH(-) in CH(3)CN or C(2)H(5)CN in a 2?:?2 ratio to give one equivalent Mo(IV)OL(x) and one equivalent Mo(VI)O(2)L(x), which is confirmed by the UV-vis and IR spectroscopies. The low temperature stopped-flow analysis allows investigations of the mechanism for the reaction of Mo(V)OL(x) with OH(-). The kinetic study for the reaction of Mo(V)OL(dmed) with OH(-) suggests that Mo(V)OL(dmed) reacts with OH(-) to give a six-coordinate oxo-hydroxo-molybdenum(v) species, Mo(V)O(OH), and, then, the resulting species undergoes successive deprotonation by another OH(-) and oxidation by a remaining Mo(V)OL(dmed) to yield the final products Mo(IV)OL(dmed) and Mo(VI)O(2)L(dmed) complexes in a 1?:?1 ratio. In this case, the Mo(V)O(2) species are involved as an intermediate in the reaction. On the other hand, in the reaction of Mo(V)OL(bdt) with OH(-), coordination of OH(-) to the Mo(V) centre to give a six-coordinate Mo(V)O(OH)L(bdt) species becomes the rate limiting step and other intermediates are not suggested. On the basis of these results, the ligand effects of the dithiolene ligands on the reactivity of the bis(dithiolene)molybdenum complexes are discussed.     

Monoanionic molybdenum and tungsten tris(dithiolene) complexes: a multifrequency EPR study

Numerous Mo and W tris(dithiolene) complexes in varying redox states have been prepared and representative examples characterized crystallographically: [M(S(2)C(2)R(2))(3)](z) [M = Mo, R = Ph, z = 0 (1) or 1- (2); M = W, R = Ph, z = 0 (4) or 1- (5); R = CN, z = 2-, M = Mo (3) or W (6)]. Changes in dithiolene C-S and C-C bond lengths for 1 versus 2 and 4 versus 5 are indicative of ligand reduction. Trigonal twist angles (Θ) and dithiolene fold angles (α) increase and decrease, respectively, for 2 versus 1, 5 versus 4. Cyclic voltammetry reveals generally two reversible couples corresponding to 0/1- and 1-/2- reductions. The electronic structures of monoanionic molybdenum tris(dithiolene) complexes have been analyzed by multifrequency (S-, X-, Q-band) EPR spectroscopy. Spin-Hamiltonian parameters afforded by spectral simulation for each complex demonstrate the existence of two distinctive electronic structure types. The first is [Mo(IV)((A)L(3)(5-?))](1-) ((A)L = olefinic dithiolene, type A), which has the unpaired electron restricted to the tris(dithiolene) unit and is characterized by isotropic g-values and small molybdenum superhyperfine coupling. The second is formulated as [Mo(V)((B)L(3)(6-))](1-) ((B)L = aromatic dithiolene, type B) with spectra distinguished by a prominent g-anisotropy and hyperfine coupling consistent with the (d(z(2)))(1) paramagnet. The electronic structure disparity is also manifested in their electronic absorption spectra. The compound [W(bdt)(3)](1-) exhibits spin-Hamiltonian parameters similar to those of [Mo(bdt)(3)](1-) and thus is formulated as [W(V)((B)L(3)(6-))](1-). The EPR spectra of [W((A)L(3))](1-) display spin-Hamiltonian parameters that suggest their electronic structure is best represented by two resonance forms {[W(IV)((A)L(3)(5-?))](1-) ? [W(V)((A)L(3)(6-))](1-)}. The contrast with the corresponding [Mo(IV)((A)L(3)(5-?))](1-) complexes highlights tungsten's preference for higher oxidation states.     

The tris(picolinate)vanadate(II) ion: Redox properties and electron transfer kinetics with cobalt(III) amines

Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 10³ M^?1) cm^?1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E_{$\text{1}\text{2}$} = ?0.448 V vs NHE, and ΔS_rc^θ = ?6 cal · mol^?1 · deg^?1. Electron transfer kinetics with [CO(en)₃]³⁺ led to k₁₂ = 3100 M^?1 s^?, ΔH^≠ = 12.4 kcal · mol^?1 and ΔS^≠ = ?0.9 cal · mol^?1 · deg^?1 (I = 0.10 M). For the related [Co(NH₃)₆]³⁺ complex, k₁₃ = 1.9 × 10⁴ M^?1 s^?1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.     

Tuning of the spin distribution between ligand- and metal-based spin: electron paramagnetic resonance of mixed-ligand molybdenum tris(dithiolene) complex anions

Electron paramagnetic resonance spectra of homoleptic and mixed-ligand molybdenum tris(dithiolene) complex anions [Mo(tfd)(m)(bdt)(n)](-) (n + m = 3; bdt = S(2)C(6)H(4); tfd = S(2)C(2)(CF(3))(2)) reveal that the spin density has mixed metal-ligand character with more ligand-based spin for [Mo(tfd)(3)](-) and a higher degree of metal-based spin for [Mo(bdt)(3)](-): the magnitude of the isotropic (95,97)Mo hyperfine interaction increases continuously, by a factor of 2.5, on going from the former to the latter. The mixed complexes fall in between, and the metal character of the spin increases with the bdt content. The experiments were corroborated by density functional theory computations, which reproduce this steady increase in metal-based character.     

Solvation effects on photochemically-induced electron transfer from tris(bipyridyl)ruthenium to methylviologen

Summary The effects of mixed solvent systems and anions on the rate of reaction of the title compounds were investigated. The results were shown to be best interpreted in terms of ion-pair formation and solvation-desolvation effects, in addition to the factors included in the outer-sphere electron transfer rate theory expounded by Marcus.     

Isomerization of DNA-bound distilbazolium ligand induced by electron transfer from photoexcited tris(1,10-phenanthroline)Ru(II)

The ability of the DNA duplex to behave as an efficient organized medium for cis-trans isomerization induced by electron transfer (ET) has been explored. Isomerization studies, luminescence quenching and DNA photocleavage assays show that photoexcited Ru(1,10-phenanthroline [phen])3(2+) transfers an electron to E,Z1,4-bis[2-(1-methylpyridinium-4-yl)vinyl]benzene (E,Z pMPVB), which subsequently undergoes one-way isomerization to E,E pMPVB. The unusual feature of the system is manifested by the lack of friction that is usually imposed on the photoisomerizable ligand by highly organized media. The apparent rate of ET in DNA increases when compared with the homogeneous solution. However, after correction for the local concentration of the reagents onto the biopolymer, the rate constant becomes independent of the DNA concentration and is at least 4 x 10(2) times smaller than that in the homogeneous aqueous solution. Using the photoinduced isomerization system, a large enhancement in the efficiency of single-strand break formation was found in plasmid DNA over that for Ru(phen)3(+2) alone using irradiation at lambda > 480 nm.     

Influence of donor-acceptor distance variation on photoinduced electron and proton transfer in rhenium(i)-phenol dyads

A homologous series of four molecules in which a phenol unit is linked covalently to a rhenium(I) tricarbonyl diimine photooxidant via a variable number of p-xylene spacers (n = 0-3) was synthesized and investigated. The species with a single p-xylene spacer was structurally characterized to get some benchmark distances. Photoexcitation of the metal complex in the shortest dyad (n = 0) triggers release of the phenolic proton to the acetonitrile/water solvent mixture; a H/D kinetic isotope effect (KIE) of 2.0 ± 0.4 is associated with this process. Thus, the shortest dyad basically acts like a photoacid. The next two longer dyads (n = 1, 2) exhibit intramolecular photoinduced phenol-to-rhenium electron transfer in the rate-determining excited-state deactivation step, and there is no significant KIE in this case. For the dyad with n = 1, transient absorption spectroscopy provided evidence for release of the phenolic proton to the solvent upon oxidation of the phenol by intramolecular photoinduced electron transfer. Subsequent thermal charge recombination is associated with a H/D KIE of 3.6 ± 0.4 and therefore is likely to involve proton motion in the rate-determining reaction step. Thus, some of the longer dyads (n = 1, 2) exhibit photoinduced proton-coupled electron transfer (PCET), albeit in a stepwise (electron transfer followed by proton transfer) rather than concerted manner. Our study demonstrates that electronically strongly coupled donor-acceptor systems may exhibit significantly different photoinduced PCET chemistry than electronically weakly coupled donor-bridge-acceptor molecules.     

A series of neutral radical CpNi(dithiolene). complexes

The heteroleptic neutral radical dithiolene complexes CpNi(dmit)., CpNi(dsit). and CpNi(dmid).(dmit=1,3-dithiole-2-thione-4,5-dithiolate; dsit=1,3-dithiole-2-thione-4,5-diselenolate; dmid=1,3-dithiole-2-one-4,5-dithiolate) are obtained from the reaction of (Cp2Ni)BF4 with either (n-Bu4N)[Ni(dmit)2] and (n-Bu4N)[Ni(dmid)2] or PhSb(dmit) and PhSb(dsit), respectively. The three complexes reduce reversibly to the corresponding Ni(II) anions and oxidize reversibly to the cationic state. As deduced from DFT calculations performed on CpNi(dmit)., the SOMO of these complexes is essentially localized on the dithiolene moiety with little metal contribution. CpNi(dsit). is isostructural with CpNi(dmit). and crystallizes in the monoclinic system, space group P2(1). In the solid-state structures of both CpNi(dmit). and CpNi(dsit)., molecules interact through a three-dimensional set of intermolecular interactions mediated by short SS, SeSe and SSe contacts, as confirmed from the temperature and field dependence of the magnetic susceptibility by the observation of an antiferromagnetic ground state below T(Neel)=27 K in CpNi(dmit)., 18 K in CpNi(dsit).. Finally, CpNi(dmid). crystallizes in the orthorhombic system, space group Pnma. Molecules organize into uniform chains through the stacking of the dmid moieties in a sigma-type face-to-face overlap.     

Photoinduced electron transfer from polystyrene pendant tris(2,2′-bipyridyl)ruthenium (II) complex to methylviologen

The characteristics of the photoinduced electron transfer reaction from polystyrene pendant tris(2,2′-bipyridyl)ruthenium (II) complex [Ru(bpy)] to methylviologen (MV²⁺) were studied. The rate constant k₁ from the excited state of the complex, Ru(bpy), to MV²⁺ were determined for both the polymeric and monomeric complexes from the lifetime τ of Ru(bpy) and the quenching rate of Ru(bpy) by MV²⁺. The polymer pendant Ru(bpy) showed three kinds of τ components ranging from 7 to 474 ns, in contrast to the monomeric complex, which showed one component of 350 ns. The k₁ values for both complexes were almost the same, on the order of 10⁸ L/mol s. The photoinduced electron transfer from solid-phase Ru(bpy) to liquid-phase MV²⁺ was realized by utilizing the polymer complex, and the solid–liquid interphase reaction system is discussed.     

Electronic structures of tris(dioxolene)chromium and tris(dithiolene)chromium complexes of the electron-transfer series [Cr(dioxolene)(3)](z) and [Cr(dithiolene)(3)](z) (z = 0, 1-, 2-, 3-). A combined experimental and density functional theoretical study

From the reaction mixture of 3,6-di-tert-butylcatechol, H2[3,6L(cat)], [CrCl3(thf)3], and NEt3 in CH3CN in the presence of air, the neutral complex [CrIII(3,6L*(sq))3] (S = 0) (1) was isolated. Reduction of 1 with [Co(Cp)2] in CH2Cl2 yielded microcrystals of [Co(Cp)2][CrIII(3,6L*(sq))2(3,6L(cat))] (S = 1/2) (2) where (3,6L*(sq)(1-) is the pi-radical monoanionic o-semiquinonate of the catecholate dianion (3,6Lcat)(2-). Electrochemistry demonstrated that both species are members of the electron-transfer series [Cr(3,6LO,O)]z (z = 0, 1-, 2-, 3-). The corresponding tris(benzo-1,2-dithiolato)chromium complex [N(n-Bu)4][CrIII(3,5L*S,S)2(3,5LS,S)] (S = 1/2) (3) has also been isolated; (3,5LS,S)(2-) represents the closed-shell dianion 3,5-di-tert-butylbenzene-1,2-dithiolate(2-), and (3,5L*S,S)(1-) is its monoanionic pi radical. Complex 3 is a member of the electron-transfer series [Cr(3,5L(S,S))3]z (z = 0, 1-, 2-, 3-). It is shown by Cr K-edge and S K-edge X-ray absorption, UV-vis, and EPR spectroscopies, as well as X-ray crystallography, of 1 and 3 that the oxidation state of the central Cr ion in each member of both electron-transfer series remains the same (+III) and that all redox processes are ligand-based. These experimental results have been corroborated by broken symmetry density functional theoretical calculations by using the B3LYP functional.     

Rapid, covalent addition of phosphine to dithiolene in a molybdenum tris(dithiolene). A new structural model for dimethyl sulfoxide reductase

Triphenylphosphine (PPh(3)) rapidly and reversibly adds to the bdt ligand in the molybdenum tris(dithiolene) complex Mo(tfd)(2)(bdt) [tfd = S(2)C(2)(CF(3))(2); bdt = S(2)C(6)H(4)], turning chelating bdt into the monodentate zwitterionic ligand SC(6)H(4)SPPh(3). A second PPh(3) molecule fills the newly created open site in the crystallographically characterized product Mo(tfd)(2)(SC(6)H(4)SPPh(3))(PPh(3)), which is a structural model for dimethyl sulfoxide (DMSO) reductase. While the complex is only a precatalyst for reduction of DMSO by PPh(3) (the initially low catalytic rate increases with time), Mo(tfd)(2)(SMe(2))(2) was found to be catalytically active without an induction period.     

Photo-induced electron transfer study of rhenium(I) bipyridyl complexes with covalently linked phenothiazine donor through different bridge

A novel rhenium(I) bipyridyl complex 1a, [(4,4’-di-COOEt-bpy)Re(CO)₃(py-NHCO-PTZ)PF₆] and a model 1b, [(4,4’-di-COOEt-bpy)Re(CO)₃(py-PTZ)PF₆] (bpy is 2, 2’-bipyridine, py-NHCO-PTZ is phenothiazine-(10-carbonyl amide) pyridine and py-PTZ is 10-(4-picolyl) phenothiazine) were synthesized. Their photo-induced electron transfer (ET) reaction with electron acceptor methyl viologen (MV²⁺) in acetonitrile was studied by nanosecond laser flash photolysis at room temperature. Photoexcitation of 1 in the presence of MV²⁺ led to ET from the Re moiety to MV²⁺ generating Re(II) and methyl viologen radical (MV^·+). Then Re(II) was reduced either by the charge recombination with MV^·+ or by intramolecular ET from the attached PTZ, regenerating the photosensitizer Re(I) and forming the PTZ radical at 510 nm. In the case of 1b, the absorption for PTZ radical can be observed distinctly accompanied intermolecular ET, whereas not much difference at 510 nm can be detected for 1a on the time scale of the experiments. This demonstrates that the linking bridge plays a key role on the intramolecular ET in complex 1.     

Sulfur-rich CpCo(dithiolene) complexes: Isostructural or non-isostructural couples of CpCo(III) with CpNi(III) dithiolene complexes

Eight new sulfur-rich [CpCo(dithiolene)] complexes were synthesized from [Zn(dmit)₂]²⁻ as a starting material. The structures, electrochemical behavior and electronic absorption spectra of the sulfur-rich [CpCo(S₂C₂S₂Y)] complexes could be compared with the early data of analogous Ni complexes. [CpCo(pddt)] (Y = -(CH₂)₃-), [CpCo(dpdt)] (Y = -CH₂C(CH₂)CH₂-), [CpCo(bddt)] (Y = -(CH₂)₄-), [CpCo(dtdt)] (Y = -CH₂SCH₂-) and [CpCo(poddt)] (Y = -CH₂C(O)CH₂-) crystallized in all isostructural with the corresponding paramagnetic [CpNi(dithiolene)] complexes, but [CpCo(dmid)] (Y = CO), [CpCo(dddt)] (Y = -(CH₂)₂-) and [CpCo(F₂pddt)] (Y = -CH₂CF₂CH₂-) crystallized in non-isostructural with them. These molecules are associated with intermolecular short S?S contacts in the crystals. [CpCo(F₂pddt)] did not show any remarkable S?S contacts but indicated interesting fluorine segregation and Cp?Cp face-to-face interactions. Redox potentials of [CpCo(dithiolene)] complexes were obtained with the cyclic voltammetry measurements and dimerized by electrochemical oxidations. Electronic absorption spectra of [CpCo(dithiolene)] complexes showed visible absorption in the range of 585-701 nm as lowest energy wavelengths (? = 9800-11,800 M⁻¹ cm⁻¹) in solutions, and they were higher energy than those of [CpNi(dithiolene)] complexes (near-IR).     

Phosphine-substituted dithiolene complexes as ligands: communication between ruthenium(II) centers through a dimolybdenum bis(dithiolene) core

The reaction of Mo2(SCH2CH2S)2Cp2 (1; Cp=eta-C5H5) with an excess of an alkyne in refluxing dichloromethane affords the bis(dithiolene) complexes Mo2(micro-SCR1=CR2S)2Cp2 (2a, R1=R2=CO2Me; 2b, R1=R2=Ph; 2c, R1=H, R2=CO2Me) whereas with 1 equiv of alkyne at room temperature the mixed dithiolene-dithiolate species Mo2(micro-SCR1=CR2S)(micro-SCH2CH2S)Cp2 (3a, R1=R2=CO2Me; 3b, R1=R2=Ph) are formed. The remaining dithiolate ligand in 3 can then be converted into a different dithiolene by reaction with a second alkyne. Applying this methodology, we have used bis(diphenylphosphino)acetylene to prepare the first examples of complexes containing phosphine-substituted dithiolene ligands: Mo2{micro-SC(CO2Me)=C(CO2Me)S}{micro-SC(PPh2)=C(PPh2)S}Cp2 (2g) and Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2 (2h). Tri- and tetrametallic complexes can then be assembled by coordination of these diphosphines to CpRuCl units by reaction with CpRu(PPh3)2Cl. Electrochemical studies of the Ru(II)/Ru(III) couple in Mo2{micro-SC(PPh2)=C(PPh2)S}2Cp2(RuClCp)2 (4b) reveals that the two separate ruthenium centers are oxidized electrochemically at different potentials, demonstrating communication between them through the dimolybdenum bis(dithiolene) core. Density functional theory calculations were carried out to explore the electronic structures of these species and to predict and assign their electronic spectra.     

The molecular structures of tris(dipivaloylmethanato)chromium and tris(dipivaloylmethanato)cobalt determined by gas electron diffraction and density functional theory calculations

The molecular structures of tris(dipivaloylmethanato)chromium and tris(dipivaloylmethanato)cobalt have been determined by quantum chemical calculations and gas electron diffraction. Both the experimental data and the theoretical results are consistent with molecular structures having D ₃ symmetry which is in agreement with the Kepert model. The experimental bond distances, r _h1(Å), and bond angles, ∠ _h1(°), are: Cr–O = 1.976(5), C–O = 1.287(3), C–C_r = 1.392(6), C–C_t = 1.547(3), OCrO = 90.1(0.9), CC_rC = 122.3(0.9), OCC_t = 114.7(0.9) and Co–O = 1.891(4), C–O = 1.269(3), C–C_r = 1.411(5), C–C_t = 1.546(3), OCoO = 95.2(0.5), CC_rC = 122.5(0.9), OCC_t = 115.1(0.8).     

Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone: synthesis,characterization, and photoinduced electron transfer reactions

Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)(3)](2+) complex have been synthesized. In triad 6 (denoted Ru(II)-BQ-Co(III)), a [Co(bpy)(3)](3+) complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-Ru(II)-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads Ru(II)-BQ (4) and PTZ-Ru(II) (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant k(f) = 5 x 10(9) s(-)(1) (tau(f) = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant k(b) approximately 4.5 x 10(8) s(-)(1) (tau(b) approximately 2.2 ns), for both Ru(II)-BQ and Ru(II)-BQ-Co(III) with no indication of a charge shift to generate the reduced Co(II) moiety. In the PTZ-Ru(II)-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 x 10(9) s(-)(1)) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ(*)(+)-Ru(II)-BQ(*)(-) state (tau = 80 ns) in unusually high yield for a [Ru(bpy)(3)](2+)-based triad (> 90%), that lies at DeltaG degrees = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ(*)(+) and the BQ(*)(-) moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-Ru(II) a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-Ru(II) state and 18% in the PTZ(*)(+)-Ru(II)(bpy(*)(-)) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ(*)(+)-Ru(II)(bpy(*)(-)) state was thus faster than what would have been inferred from the Ru(II) emission decay (tau = 90 ns). This result suggests that reports for related PTZ-Ru(II) and PTZ-Ru(II)-acceptor complexes in the literature might need to be reconsidered.