Nitric oxide production by visible light irradiation of aqueous solution of nitrosyl ruthenium complexes

[Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](PF(6))(5) (L is NH(3), py, or 4-acpy) was prepared with good yields in a straightforward way by mixing an equimolar ratio of cis-[Ru(NO(2))(bpy)(2)(NO)](PF(6))(2), sodium azide (NaN(3)), and trans-[RuL(NH(3))(4)(pz)] (PF(6))(2) in acetone. These binuclear compounds display nu(NO) at ca. 1945 cm(-)(1), indicating that the nitrosyl group exhibits a sufficiently high degree of nitrosonium ion (NO(+)). The electronic spectrum of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex in aqueous solution displays the bands in the ultraviolet and visible regions typical of intraligand and metal-to-ligand charge transfers, respectively. Cyclic voltammograms of the binuclear complexes in acetonitrile give evidence of three one-electron redox processes consisting of one oxidation due to the Ru(2+/3+) redox couple and two reductions concerning the nitrosyl ligand. Flash photolysis of the [Ru(II)L(NH(3))(4)(pz)Ru(II)(bpy)(2)(NO)](5+) complex is capable of releasing nitric oxide (NO) upon irradiation at 355 and 532 nm. NO production was detected and quantified by an amperometric technique with a selective electrode (NOmeter). The irradiation at 532 nm leads to NO release as a consequence of a photoinduced electron transfer. All species exhibit similar photochemical behavior, a feature that makes their study extremely important for their future application in the upgrade of photodynamic therapy in living organisms.     

Reactivity of radicals generated on irradiation of trans-[Ru(NH3)4(NO2)P(OEt)3](PF6)

The electronic absorption spectrum of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in aqueous solution is characterized by a strong absorption band at 334 nm (lambda(max) = 1800 mol(-1) L cm(-1)). On the basis of quantum mechanics calculations, this band has been assigned to a MLCT transition from the metal to the nitro ligand. Molecular orbital calculations also predict an LF transition at 406 nm, which is obscured by the intense MLCT transition. When trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in acetonitrile is irradiated with a 355 nm pulsed laser light, the absorption features are gradually shifted to represent those of the solventocomplex trans-[Ru(NH(3))(4)(solv)(P(OEt)(3)](2+) (lambda(max) = 316 nm, epsilon = 650 mol(-1) L cm(-1)), which was also detected by (31)P NMR spectroscopy. The net photoreaction under these conditions is a photoaquation of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+), although, after photolysis, the presence of the nitric oxide was detected by differential pulse polarography. In phosphate buffer pH 9.0, after 15 min of photolysis, a thermal reaction resulted in the formation of a hydroxyl radical and a small amount of a paramagnetic species as detected by EPR spectroscopy. In the presence of trans-[Ru(NH(3))(4)(solv)P(OEt)(3)](2+), the hydroxyl radical initiated a chain reaction. On the basis of spectroscopic and electrochemical data, the role of the radicals produced is analyzed and a reaction sequence consistent with the experimental results is proposed. The 355 nm laser photolysis of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in phosphate buffer pH 7.4 also gives nitric oxide, which is readily trapped by ferrihemeproteins (myoglobin, hemoglobin, and cytochrome C), giving rise to the formation of their nitrosylhemeproteins(II), (NO)Fe(II)hem.     

X-ray Crystallographic Study of the Ruthenium Blue Complexes [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2): Steric Interactions and the Ru-Ru "Bond Length"

X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions.     

Ruthenium(II)-polyazine light absorbers bridged to reactive cis-dichlororhodium(III) centers in a bimetallic molecular architecture

Bimetallic complexes of the form [(bpy)(2)Ru(BL)RhCl(2)(phen)](PF(6))(3), where bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and BL = 2,3-bis(2-pyridyl)pyrazine (dpp) or 2,2'-bipyrimidine (bpm), were synthesized, characterized, and compared to the [{(bpy)(2)Ru(BL)}(2)RhCl(2)](PF(6))(5) trimetallic analogues. The new complexes were synthesized via the building block method, exploiting the known coordination chemistry of Rh(III) polyazine complexes. In contrast to [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) and [{(bpy)(2)Ru(bpm)}(2)RhCl(2)](PF(6))(5), [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) have a single visible light absorber subunit coupled to the cis-Rh(III)Cl(2) moiety, an unexplored molecular architecture. The electrochemistry of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) showed a reversible oxidation at 1.61 V (vs Ag/AgCl) (Ru(III/II)), quasi-reversible reductions at -0.39 V, -0.74, and -0.98 V. The first two reductive couples corresponded to two electrons, consistent with Rh reduction. The electrochemistry of [(bpy)(2)Ru(bpm)RhCl(2)(phen)](PF(6))(3) exhibited a reversible oxidation at 1.76 V (Ru(III/II)). A reversible reduction at -0.14 V (bpm(0/-)), and quasi-reversible reductions at -0.77 and -0.91 V each corresponded to a one electron process, bpm(0/-), Rh(III/II), and Rh(II/I). The dpp bridged bimetallic and trimetallic display Ru(dpi)-->dpp(pi*) metal-to-ligand charge transfer (MLCT) transitions at 509 nm (14,700 M(-1) cm(-1)) and 518 nm (26,100 M(-1) cm(-1)), respectively. The bpm bridged bimetallic and trimetallic display Ru(dpi)-->bpm(pi*) charge transfer (CT) transitions at 581 nm (4,000 M(-1) cm(-1)) and 594 nm (9,900 M(-1) cm(-1)), respectively. The heteronuclear complexes [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) and [{(bpy)(2)Ru(dpp)}(2)RhCl(2)](PF(6))(5) had (3)MLCT emissions that are Ru(dpi)-->dpp(pi*) CT in nature but were red-shifted and lower intensity than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4). The lifetimes of the (3)MLCT state of [(bpy)(2)Ru(dpp)RhCl(2)(phen)](PF(6))(3) at room temperature (30 ns) was shorter than [(bpy)(2)Ru(dpp)Ru(bpy)(2)](PF(6))(4), consistent with favorable electron transfer to Rh(III) to generate a metal-to-metal charge-transfer ((3)MMCT) state. The reported synthetic methods provide means to a new molecular architecture coupling a single Ru light absorber to the Rh(III) center while retaining the interesting cis-Rh(III)Cl(2) moiety.     

Nitrosyl induces phosphorous-acid dissociation in ruthenium(II)

The trans-[Ru(NO)(NH(3))(4)(P(OH)(3))]Cl(3) complex was synthesized by reacting [Ru(H(2)O)(NH(3))(5)](2+) with H(3)PO(3) and characterized by spectroscopic ((31)P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol(-1) cm(-1); λ = 319 nm, ε = 773 L mol(-1) cm(-1); λ = 241 nm, ε = 1385 L mol(-1) cm(-1); ν(NO(+)) = 1879 cm(-1)). A pK(a) of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) + H(2)O ? trans-[Ru(NO)(NH(3))(4)(P(O(-))(OH)(2))](2+) + H(3)O(+). According to (31)P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) yields the O-bonded linkage isomer trans- [Ru(NO)(NH(3))(4)(OP(OH)(2))](2+), then the trans-[Ru(NO)(NH(3))(4)(OP(H)(OH)(2))](3+) decays to give the final products H(3)PO(3) and trans-[Ru(NO)(NH(3))(4)(H(2)O)](3+). The dissociation of phosphorous acid from the [Ru(NO)(NH(3))(4)](3+) moiety is pH dependent (k(obs) = 2.1 × 10(-4) s(-1) at pH 3.0, 25 °C).     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

Electropolymerization of vinylbipyridine complexes of ruthenium(II) and osmium(II) in SiO2 sol-gel films

PF(6)(-) salts of the complexes [Ru(vbpy)(3)](2+) and [Os(vbpy)(3)](2+) (vbpy = 4-methyl-4'-vinyl-2,2'-bipyridine) have been electropolymerized into the pores of SiO(2) sol-gel films deposited on conductive Tin(IV)-doped indium oxide-coated glass slides (ITO, In(2)O(3):Sn). The resulting transparent composites represent a new class of materials of general formulas ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) and ITO/SG-poly-[Os(vbpy)(3)](PF(6))(2). The composites are stable with respect to loss of complexes to the external solution and demonstrate several interesting phenomena: (1) Sol-gel pores, serving as diffusion channels for the vbpy complexes and counterions, play a key role in the formation of the polymer and dictate the electrochemical properties of the resulting composite. (2) Dynamic polymer growth occurs within individual diffusion channels creating parallel structures of filled and unfilled channels. (3) Unidirectional charge transfer and a "bilayer" effect have been shown to operate in ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) films exposed to [Os(vbpy)(3)](PF(6))(2) in the external solution. (4) Photophysical properties of the metal-to-ligand charge transfer (MLCT) excited states in ITO/SG-poly-[Ru(vbpy)(3)](PF(6))(2) composites are significantly modified compared to electropolymerized films on ITO or model monomeric complexes in solution.     

1H NMR, electron paramagnetic resonance, and density functional theory study of dinuclear pentaammineruthenium dicyanamidobenzene complexes

Paramagnetic (1)H NMR and electron paramagnetic resonance (EPR) spectroscopies and density functional theory (DFT) spin density calculations were selectively performed on the [{(NH(3))(5)Ru}(2)(μ-L)](3+,?4+,?5+) complexes, where L is 2,3,5,6-tetrachloro-, 2,5-dichloro-, 2,5-dimethyl-, and unsubstituted 1,4-dicyanamidobenzene dianion, to characterize the electronic structure of these complexes. EPR spectra of the [{(NH(3))(5)Ru}(2)(μ-L)](3+) complexes in N,N'-dimethylformamide at 4 K showed a ruthenium axial signal, and thus the complexes are [Ru(II),L(2-), Ru(III)] mixed-valence systems. DFT spin density calculations of [{(NH(3))(5)Ru}(2)(μ-L)](3+) where L = 1,4-dicyanamidobenzene dianion gave mostly bridging-ligand centered spin distribution for both vacuum and implicit solvent calculations, in poor agreement with EPR, but more realistic results were obtained when explicit electrostatic interactions between solute and solvent were included in modeling. For the [{(NH(3))(5)Ru}(2)(μ-L)](4+) complexes, EPR spectroscopy showed no signal down to 4 K. Nevertheless, solvent-dependent (1)H NMR data and analysis support a [Ru(III),L(2-), Ru(III)] state. Hyperfine coupling constants (A(c)/h) of trans- and cis-ammine and phenyl hydrogens were determined to be 17.2, 3.8, and -1.5 MHz respectively. EPR studies of the [{(NH(3))(5)Ru}(2)(μ-L)](5+) complexes showed a metal-radical axial signal and based on previously published (1)H NMR data, a [Ru(IV),L(2-), Ru(III)] state is favored over a [Ru(III),L(-), Ru(III)] state.     

The synthesis and structure of heteroleptic tris(diimine)ruthenium(II) complexes

The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.     

Light-induced metastable linkage isomers of ruthenium sulfur dioxide complexes

The irradiation of ruthenium-sulfur dioxide complexes of general formula trans-[Ru(II)(NH(3))(4)(SO(2))X]Y with laser light at low temperature results in linkage isomerization of SO(2), starting with eta(1)-planar S-bound to eta(2)-side S,O-bound SO(2). The solid-state photoreaction proceeds with retention of sample crystallinity. Following work on trans-[Ru(NH(3))(4)Cl(eta(1)-SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(eta(1)-SO2)](C(6)H(5)SO(3))(2) (Kovalevsky, A. Y.; Bagley, K. A.; Coppens, P. J. Am. Chem. Soc. 2002, 124, 9241-9248), we describe photocrystallographic, IR, DSC, and theoretical studies of trans-[Ru(II)(NH(3))(4)(SO(2))X]Y complexes with (X = Cl(-), H(2)O, or CF(3)COO(-) (TFA(-))) and a number of different counterions (Y = Cl(-), C(6)H(5)SO(3)(-), Tos(-), or TFA(-)). Low temperature IR experiments indicate the frequency of the asymmetric and symmetric stretching vibrations of the Ru-coordinated SO(2) to be downshifted by about 100 and 165 cm(-1), respectively. Variation of the trans-to-SO(2) ligand and the counterion increases the MS2 decay temperature from 230 K (trans-[Ru(II)(NH(3))(4)(SO(2))Cl]Cl) to 276 K (trans-[Ru(II)(NH(3))(4)(SO(2))(H(2)O)](Tos)(2)). The stability of the MS2 state correlates with increasing sigma-donating ability of the trans ligand and the size of the counterion. Quantum chemical DFT calculations indicate the existence of a third eta(1)-O-bound (MS1) isomer, the two metastable states being 0.1-0.6 eV above the energy of the ground-state complex.     

Enhancement of metal-metal coupling at a considerable distance by using 4-pyridinealdazine as a bridging ligand in polynuclear complexes of rhenium and ruthenium

Novel polynuclear complexes of rhenium and ruthenium containing PCA (PCA = 4-pyridinecarboxaldehyde azine or 4-pyridinealdazine or 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) as a bridging ligand have been synthesized as PF(6-) salts and characterized by spectroscopic, electrochemical, and photophysical techniques. The precursor mononuclear complex, of formula [Re(Me(2)bpy)(CO)(3)(PCA)](+) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), does not emit at room temperature in CH(3)CN, and the transient spectrum found by flash photolysis at lambda(exc) = 355 nm can be assigned to a MLCT (metal-to-ligand charge transfer) excited state [(Me(2)bpy)(CO)(3)Re(II)(PCA(-))](+), with lambda(max) = 460 nm and tau < 10 ns. The spectral properties of the related complexes [[Re(Me(2)bpy)(CO)(3)}(2)(PCA)](2+), [Re(CO)(3)(PCA)(2)Cl], and [Re(CO)(3)Cl](3)(PCA)(4) confirm the existence of this low-energy MLCT state. The dinuclear complex, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(II)(NH(3))(5)](3+), presents an intense absorption in the visible spectrum that can be assigned to a MLCT d(pi)(Ru) --> pi(PCA); in CH(3)CN, the value of lambda (max) = 560 nm is intermediate between those determined for [Ru(NH(3))(5)(PCA)](2+) (lambda(max) = 536 nm) and [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](4+) (lambda(max) = 574 nm), indicating a significant decrease in the energy of the pi-orbital of PCA. The mixed-valent species, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(III)(NH(3))(5)](4+), was obtained in CH(3)CN solution, by bromine oxidation or by controlled-potential electrolysis at 0.8 V in a OTTLE cell of the [Re(I),Ru(II)] precursor; the band at lambda(max) = 560 nm disappears completely, and a new band appears at lambda(max) = 483 nm, assignable to a MMCT band (metal-to-metal charge transfer) Re(I) --> Ru(III). By using the Marcus-Hush formalism, both the electronic coupling (H(AB)) and the reorganization energy (lambda) for the metal-to-metal intramolecular electron transfer have been calculated. Despite the considerable distance between both metal centers (approximately 15.0 Angstroms), there is a moderate coupling that, together with the comproportionation constant of the mixed-valent species [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](5+) (K(c) approximately 10(2), in CH(3)CN), puts into evidence an unusual enhancement of the metal-metal coupling in the bridged PCA complexes. This effect can be accounted for by the large extent of "metal-ligand interface", as shown by DFT calculations on free PCA. Moreover, lambda is lower than the driving force -DeltaG degrees for the recombination charge reaction [Re(II),Ru(II)] --> [Re(I),Ru(III)] that follows light excitation of the mixed-valent species. It is then predicted that this reverse reaction falls in the Marcus inverted region, making the heterodinuclear [Re(I),Ru(III)] complex a promising model for controlling the efficiency of charge-separation processes.     

Synthesis, structures, and properties of ruthenium(II) complexes of N-(1,10-phenanthrolin-2-yl)imidazolylidenes

Mononuclear ruthenium complexes [RuCl(L1)(CH(3)CN)(2)](PF(6)) (2a), [RuCl(L2)(CH(3)CN)(2)](PF(6)) (2b), [Ru(L1)(CH(3)CN)(3)](PF(6))(2) (4a), [Ru(L2)(CH(3)CN)(3)](PF(6))(2) (4b), [Ru(L2)(2)](PF(6))(2) (5), [RuCl(L1)(CH(3)CN)(PPh(3))](PF(6)) (6), [RuCl(L1)(CO)(2)](PF(6)) (7), and [RuCl(L1)(CO)(PPh(3))](PF(6)) (8), and a tetranuclear complex [Ru(2)Ag(2)Cl(2)(L1)(2)(CH(3)CN)(6)](PF(6))(4) (3) containing 3-(1,10-phenanthrolin-2-yl)-1-(pyridin-2-ylmethyl)imidazolylidene (L1) and 3-butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene (L2) have been prepared and fully characterized by NMR, ESI-MS, UV-vis spectroscopy, and X-ray crystallography. Both L1 and L2 act as pincer NNC donors coordinated to ruthenium (II) ion. In 3, the Ru(II) and Ag(I) ions are linked by two bridging Cl(-) through a rhomboid Ag(2)Cl(2) ring with two Ru(II) extending to above and down the plane. Complexes 2-8 show absorption maximum over the 354-428 nm blueshifted compared to Ru(bpy)(3)(2+) due to strong σ-donating and weak π-acceptor properties of NHC ligands. Electrochemical studies show Ru(II)/Ru(III) couples over 0.578-1.274 V.     

Trinuclear pyrazine-bridged ruthenium complexes: syntheses, electrochemistry, NIR-Vis spectra, and their interpretation in terms of a 5-orbital-3-parameter model

A study of absorption spectra in the near-infrared (NIR) and visible (vis) regions of trinuclear Ru complexes containing pyrazine (pyz) as bridging ligand, trans-[(Ru(NH(3))(5)pyz)(2)Ru(NH(3))(4)](m+)(m = 6-9), is reported. The spectra were recorded on aqueous solutions containing the described species formed in situ by stoichiometric additions of a standard solution of Ce(SO(4))(2). They were interpreted in terms of a simple 5-orbital-3-parameter model which includes the effects of d-pi interaction and electronic correlation. The model is shown to account for the observed NIR-vis spectra of the complex ions. The 6+ parent species was synthesized by an improved literature method and fully characterized. The novel 8+ complex was also prepared and characterized. The 9+ ion was established to be slowly reduced by water, with dioxygen formation. Electrochemical (CV and DPV) studies were performed on the trinuclear 6+ complex, as well as on its constituent fragments [Ru(NH(3))(5)(pyz)](2+) and trans-[Ru(NH(3))(4)(pyz)(2)](2+).     

General synthesis of (salen)ruthenium(III) complexes via N...N coupling of (salen)ruthenium(VI) nitrides

Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.     

Picosecond isomerization in photochromic ruthenium-dimethyl sulfoxide complexes

The complexes [Ru(tpy)(bpy)(dmso)](OSO(2)CF(3))(2) and trans-[Ru(tpy)(pic)(dmso)](PF(6)) (tpy is 2,2':6',2' '-terpyridine, bpy is 2,2'-bipyridine, pic is 2-pyridinecarboxylate, and dmso is dimethyl sulfoxide) were investigated by picosecond transient absorption spectroscopy in order to monitor excited-state intramolecular S-->O isomerization of the bound dmso ligand. For [Ru(tpy)(bpy)(dmso)](2+), global analysis of the spectra reveals changes that are fit by a biexponential decay with time constants of 2.4 +/- 0.2 and 36 +/- 0.2 ps. The first time constant is assigned to relaxation of the S-bonded (3)MLCT excited state. The second time constant represents both excited-state relaxation to ground state and excited-state isomerization to form O-[Ru(tpy)(bpy)(dmso)](2+). In conjunction with the S-->O isomerization quantum yield (Phi(S)(-->)(O) = 0.024), isomerization of [Ru(tpy)(bpy)(dmso)](2+) occurs with a time constant of 1.5 ns. For trans-[Ru(tpy)(pic)(dmso)](+), global analysis of the transient spectra reveals time constants of 3.6 +/- 0.2 and 118 +/- 2 ps associated with these two processes. In conjunction with the S-->O isomerization quantum yield (Phi(S)(-->)(O) = 0.25), isomerization of trans-[Ru(tpy)(pic)(dmso)](+) occurs with a time constant of 480 ps. In both cases, the thermally relaxed excited states are assigned as terpyridine-localized (3)MLCT states. Electronic state diagrams are compiled employing these data as well as electrochemical, absorption, and emission data to describe the reactivity of these complexes. The data illustrate that rapid bond-breaking and bond-making reactions can occur from (3)MLCT excited states formed from visible light irradiation.     

Synthesis of ruthenium(II) complexes of tetradentate bis(N-pyridylimidazolylidenyl)methane and their reactivities towards N- donors

A family of hexa-coordinated ruthenium(II) complexes of bis(N-pyridylimidazolylidenyl)methane (L) were prepared and structurally characterized. Carbene transfer reactions of [Ru(p-cymene)Cl(2)](2), [Ru(CO)(2)Cl(2)](n) and RuHCl(CO)(PPh(3))(3) with silver-NHC complexes in situ generated from [H(2)L](PF(6))(2) and Ag(2)O afforded [RuL(CH(3)CN)(2)](PF(6))(2) (1), [Ru(2)L(p-cymene)(2)Cl(2)](PF(6))(2) (2), [RuL(CO)(2)](PF(6))(2) (3) and [RuL(PPh(3))(2)](PF(6))(2) (4), respectively. The reactions of 1 towards several N- and P-donors were studied. The treatment of 1 with 1,10-phenanthroline resulted in the substitution of one pyridine and one acetonitrile molecule affording [RuL(phen)(CH(3)CN)](PF(6))(2) (5) as a mixture of two isomers. Reaction of 1,2-bis(diphenylphosphino)ethane (dppe) and 1 gave [RuL(dppe)(CH(3)CN)(2)](PF(6))(2) (7), in which two pyridines were substituted by a dppe ligand trans to two NHC groups. In contrast, reactions of 1 with ethane-1,2-diamine, propane-1,3-diamine and 3,5-dimethyl-1H-pyrazole led to the substitution of acetonitrile and subsequent N-H addition of the C≡N bond of the coordinated acetonitrile yielding [RuL(ethane-1,2-diamine)(N-(2-aminoethyl)acetimidamide)](PF(6))(2) (8), [RuL(propane-1,3-diamine)(N-(3-aminopropyl)acetimidamide)](PF(6))(2) (9) and RuL(1-(3,5-dimethyl-1H-pyrazol-1-yl)ethanimine)(CH(3)CN)](PF(6))(2) (10), respectively.     

Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes

We report the synthesis of free 1,6,7,12-tetraazaperylene (tape). Tape was obtained from 1,1'-bis-2,7-naphthyridine by potassium promoted cyclization followed by oxidation with air. Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes of the general formulas [Ru(L-L)(2)(tape)](PF(6))(2), [1](PF(6))(2)-[5](PF(6))(2), and [{Ru(L-L)(2)}(2)(μ-tape)](PF(6))(4), [6](PF(6))(4)-[10](PF(6))(4), with{L-L = phen, bpy, dmbpy (4,4'-dimethyl-2,2'-bipyridine), dtbbpy (4,4'-ditertbutyl-2,2'-bipyridine) and tmbpy (4,4'5,5'-tetramethyl-2,2'-bipyridine)}, respectively, were synthesized. The X-ray structures of tape·2CHCl(3) and the mononuclear complexes [Ru(bpy)(2)(tape)](PF(6))(2)·0.5CH(3)CN·0.5toluene, [Ru(dmbpy)(2)(tape)](PF(6))(2)·2toluene and [Ru(dtbbpy)(2)(tape)](PF(6))(2)·3acetone·0.5H(2)O were solved. The UV-vis absorption spectra and the electrochemical behavior of the ruthenium(ii) tape complexes were explored and compared with the data of the analogous dibenzoeilatin (dbneil), 2,2'-bipyrimidine (bpym) and tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazin (tpphz) species.     

Luminescent ruthenium(II) polypyridine biotin complexes: synthesis, characterization, photophysical and electrochemical properties, and avidin-binding studies

Two luminescent ruthenium(II) polypyridine complexes containing a biotin moiety [Ru(bpy)(2)(L1)](PF(6))(2) (1) and [Ru(bpy)(2)(L2)](PF(6))(2) (2) (bpy = 2,2'-bipyridine; L1 = 4-(N-((2-biotinamido)ethyl)amido)-4'-methyl-2,2'-bipyridine; L2 = 4-(N-((6-biotinamido)hexyl)amido)-4'-methyl-2,2'-bipyridine) have been synthesized and characterized, and their photophysical and electrochemical properties have been studied. Upon photoexcitation, complexes 1 and 2 display intense and long-lived triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ru) --> pi*(L1 or L2)) emission in fluid solutions at 298 K and in low-temperature glass. We have studied the binding of these ruthenium(II) biotin complexes to avidin by 4'-hydroxyazobenzene-2-carboxylic acid (HABA) assays, luminescence titrations, competitive assays using native biotin, and quenching experiments using methyl viologen. On the basis of the results of these experiments, a homogeneous competitive assay for biotin has been investigated.     

Structures, spectroscopic properties and redox potentials of quaterpyridyl Ru(II) photosensitizer and its derivatives for solar energy cell: a density functional study

Scalar relativistic density functional theory (DFT) has been used to explore the spectroscopic and redox properties of Ruthenium-type photovoltaic sensitizers, trans-[Ru((R)L)(NCS)(2)] ((R)L = 4,4'-di-R-4',4'-bis(carboxylic acid)-2,2' : 6',2' : 6',2'-quaterpyridine, R = H (1), Me (2), (t)Bu (3) and COOH (4); (R)L = 4,4'-di-R-4',4'-bis(carboxylic acid)-cycloquaterpyridine, R = COOH (5)). The geometries of the molecular ground, univalent cationic and triplet excited states of 1-5 were optimized. In complexes 1-4, the quaterpyridine ligand retains its planarity in the molecular, cationic and excited states, although the C≡N-Ru angle representing the SCN → Ru coordination approaches 180° in the univalent cationic and triplet excited states. The theoretically designed complex 5 displays a curved cycloquaterpyridine ligand with significantly distorted SCN → Ru coordination. The electron spin density distributions reveal that one electron is removed from the Ru/NCS moieties upon oxidation and the triplet excited state is due to the Ru/NCS → polypyridine charge transfer (MLCT/L'LCT). The experimental absorption spectra were well reproduced by the time-dependent DFT calculations. In the visible region, two MLCT/L'LCT absorption bands were calculated to be at 652 and 506 nm for 3, agreeing with experimental values of 637 and 515 nm, respectively. The replacement of the R- group with -COOH stabilizes the lower-energy unoccupied orbitals of π* character in the quaterpyridine ligand in 4. This results in a large red shift for these two MLCT/L'LCT bands. In contrast, the lower-energy MLCT/L'LCT peak of 5 nearly disappears due to the introduction of cycloquaterpyridine ligand. The higher energy bands in 5 however become broader and more intense. As far as absorption in the visible region is concerned, the theoretically designed 5 may be a very promising sensitizer for DSSC. In addition, the redox potentials of 1-5 were calculated and discussed, in conjunction with photosensitizers such as cis-[Ru(L(1))(2)(X)(2)] (L(1) = 4,4'-bis(carboxylic acid)-2,2'-bipyridine; X = NCS(-) (6), Cl(-) (7) and CN(-) (8)), cis-[Ru(L(1)')(2)(NCS)(2)] (L(1)' = 4,7-bis(carboxylic acid)-1,10-phenanthroline, 9), [NH(4)][Ru(L(2))(NCS)(3)] (L(2) = 4,4',4'-tris(carboxylic acid)-2,2' : 6',2'-terpyridine, 10) and [Ru(L(2))(NCS)(3)](-) (11).     

Design aspects for the development of mixed-metal supramolecular complexes capable of visible light induced photocleavage of DNA

Mixed-metal supramolecular complexes that couple ruthenium or osmium based light absorbers to a central rhodium(III) core have been designed which photocleave DNA upon irradiation with visible light. The complexes [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5), [[(bpy)(2)Os(dpp)](2)RhCl(2)](PF(6))(5), and [[(tpy)RuCl(dpp)](2)RhCl(2)](PF(6))(3), where bpy = 2,2'-bipyridine, tpy = 2,2':6',2' '-terpyridine, and dpp = 2,3-bis(2-pyridyl)pyrazine, all exhibit intense metal to ligand charge transfer (MLCT) based transitions in the visible but possess lower lying metal to metal charge transfer (MMCT) excited states. These supramolecular complexes with low lying MMCT states photocleave DNA when excited into their intense MLCT transitions. Structurally similar complexes without this low lying MMCT state do not exhibit DNA photocleavage, establishing the role of this MMCT state in the DNA photocleavage event. Design considerations necessary to produce functional DNA photocleavage agents are presented herein.