Photophysical, electrochemical and anion sensing properties of Ru(II) bipyridine complexes with 2,2'-biimidazole-like ligand

A new anion sensor [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3) (bpy is 2, 2'-bipyridine and DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) has been developed. Its photophysical, electrochemical and anion sensing properties are compared with two previously investigated systems, [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1) and [Ru(bpy)(2)(BbimH(2))](PF(6))(2) (2) (BiimH(2) is 2,2'-biimidazole and BbimH(2) is 2,2'-bibenzimidazole). The high acidity of the N-H fragments in these complexes make them easy to be deprotonated by strong basic anions such as F(-) and OAc(-), and they form N-H···X hydrogen bonds with weak basic anions like Cl(-), Br(-), I(-), NO(3)(-), and HSO(4)(-). Complex 3 displays strong hydrogen bonding with these 5 weak basic anions, with binding constants between 17,000 and 21,000, which are larger than those observed in complex 1, with binding constants between 3300 and 5700, and in complex 2, which shows no hydrogen bonding toward Cl(-), Br(-), I(-), and NO(3)(-), and forms considerable hydrogen bonds with HSO(4)(-) with a binding constant of 11,209. These hydrogen bonding behaviours give different NMR, emission and electrochemical responses. The different anion binding affinity of these complexes may be mainly attributed to their different pK(a1) values, 7.2 for 1, 5.7 for 2, and 6.2 for 3. The additional methyl groups at the 7 and 7' positions of complex 3 may also play an important role in the enhancement of anion binding strength.     

Coupling of metal-based light-harvesting antennas and electron-donor subunits: trinuclear ruthenium(II) complexes containing tetrathiafulvalene-substituted polypyridine ligands

Three new tetrathiafulvalene-substituted 2,2'-bipyridine ligands, cis-bpy-TTF(1), trans-bpy-TTF(1), and cis-bpy-TTF(2) have been prepared and characterized. X-ray analysis of trans-bpy-TTF(1) is also reported. Such ligands have been used to prepare two new trinuclear Ru(II) complexes, namely, [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy-TTF(1))](PF(6))(6) (9; bpy=2,2'-bipyridine; 2,3-dpp=2,3-bis(2'-pyridyl)pyrazine) and [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy-TTF(2))](PF(6))(6) (10). These compounds can be viewed as coupled antennas and charge-separation systems, in which the multichromophoric trinuclear metal subunits act as light-harvesting antennas and the tetrathiafulvalene electron donors can induce charge separation. The absorption spectra, redox behavior, and luminescence properties (both at room temperature in acetonitrile and at 77 K in a rigid matrix of butyronitrile) of the trinuclear metal complexes have been studied. For the sake of completeness, the mononuclear compounds [(bpy)(2)Ru(bpy-TTF(1))](PF(6))(2) (7) and [(bpy)(2)Ru(bpy-TTF(2))](PF(6))(2) (8) were also synthesized and studied. The properties of the tetrathiafulvalene-containing species were compared to those of the model compounds [Ru(bpy)(2)(4,4'-Mebpy)](2+) (4,4'-Mebpy=4,4'-dimethyl-2,2'-bipyridine) and [[(bpy)(2)Ru(micro-2,3-dpp)](2)Ru(bpy)](6+). The absorption spectra and redox behavior of all the new metal compounds can be interpreted by a multicomponent approach, in which specific absorption features and redox processes can be assigned to specific subunits of the structures. The luminescence properties of the complexes in rigid matrices at 77 K are very similar to those of the corresponding model compounds without TTF moieties, whereas the new species are nonluminescent, or exhibit very weak emissions relative to those of the model compounds in fluid solution at room temperature. Time-resolved transient absorption spectroscopy confirmed that the potentially luminescent MLCT states of 7-10 are significantly shorter lived than the corresponding states of the model species. Photoinduced electron-transfer processes from the TTF moieties to the (excited) MLCT chromophore(s) are held responsible for the quenching processes.     

Structural, electronic, and acid/base properties of [Ru(bpy)2(bpy(OH)2)]2+ (bpy = 2,2'-bipyridine, bpy(OH)2 = 4,4'-dihydroxy-2,2'-bipyridine)

We have synthesized the complex [Ru(bpy)(2)(bpy(OH)(2))](2+) (bpy =2,2'-bipyridine, bpy(OH)(2) = 4,4'-dihydroxy-2,2'-bipyridine). Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of the complex, with particular attention paid toward the effects of deprotonation on these properties. The most distinguishing feature observed in the X-ray structural data is a shortening of the CO bond lengths in the modified ligand upon deprotonation. Similar results are also observed in the computational studies as the CO bond becomes double bond in character after deprotonating the complex. Electrochemically, the hydroxy-modified bipyridyl ligand plays a significant role in the redox properties of the complex. When protonated, the bpy(OH)(2) ligand undergoes irreversible reduction processes; however, when deprotonated, reduction of the substituted ligand is no longer observed, and several new irreversible oxidation processes associated with the modified ligand arise. pH studies indicate [Ru(bpy)(2)(bpy(OH)(2))](2+) has two distinct deprotonations at pK(a1) = 2.7 and pK(a2) = 5.8. The protonated [Ru(bpy)(2)(bpy(OH)(2))](2+) complex has a characteristic UV/Visible absorption spectrum similar to the well-studied complex [Ru(bpy)(3)](2+) with bands arising from Metal-to-Ligand Charge Transfer (MLCT) transitions. When the complex is deprotonated, the absorption spectrum is altered significantly and becomes heavily solvent dependent. Computational methods indicate that the deprotonated bpy(O(-))(2) ligand mixes heavily with the metal d orbitals leading to a new absorption manifold. The transitions in the complex have been assigned as mixed Metal-Ligand to Ligand Charge Transfer (MLLCT).     

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.     

Reversible molecular switching of ruthenium bis(bipyridyl) groups bonded to oligothiophenes: effect on electrochemical and spectroscopic properties

We report the preparation of complexes in which ruthenium(II) bis(bipyridyl) groups are coordinated to oligothiophenes via a diphenylphosphine linker and a thienyl sulfur (P,S bonding) to give [Ru(bpy)(2)PT(3)-P,S](PF(6))(2) (bpy = 2,2'-bipyridyl, PT(3) = 3'-(diphenylphosphino)-2,2':5',2' '-terthiophene), [Ru(bpy)(2)PMeT(3)-P,S](PF(6))(2) (PMeT(3) = 3'-(diphenylphosphino)-5-methyl-2,2':5',2' '-terthiophene), [Ru(bpy)(2)PMe(2)T(3)-P,S](PF(6))(2) (PMe(2)T(3) = 5,5' '-dimethyl-3'-(diphenylphosphino)-2,2':5',2' '-terthiophene), and [Ru(bpy)(2)PDo(2)T(5)-P,S](PF(6))(2) (PDo(2)T(5) = 3,3' ' '-didodecyl-3' '-diphenylphosphino-2,2':5',2' ':5' ',2' ':5' ',2' ' '-pentathiophene). These complexes react with base, resulting in the complexes [Ru(bpy)(2)PT(3)-P,C]PF(6), [Ru(bpy)(2)PMeT(3)-P,C]PF(6), [Ru(bpy)(2)PMe(2)T(3)-P,C]PF(6), and [Ru(bpy)(2)PDo(2)T(5)-P,C]PF(6), where the thienyl carbon is bonded to ruthenium (P,C bonding). The P,C complexes revert back to the P,S bonding mode by reaction with acid; therefore, metal-thienyl bonding is reversibly switchable. The effect of interaction of the metal groups in the different bonding modes with the thienyl backbone is reflected by changes in alignment of the thienyl rings in the solid-state structures of the complexes, the redox potentials, and the pi --> pi transitions in solution. Methyl substituents attached to the terthiophene groups allow observation of the effect of these substituents on the conformational and electronic properties and aid in assignments of the electrochemical data. The PT(n)() ligands bound in P,S and P,C bonding modes also alter the electrochemical and spectroscopic properties of the ruthenium bis(bipyridyl) group. Both bonding modes result in quenching of the oligothiophene luminescence. Weak, short-lived Ru --> bipyridyl MLCT-based luminescence is observed for [Ru(bpy)(2)PDo(2)T(5)-P,S](PF(6))(2), [Ru(bpy)(2)PT(3)-P,C]PF(6), [Ru(bpy)(2)PMeT(3)-P,C]PF(6), and [Ru(bpy)(2)PMe(2)T(3)-P,C]PF(6), and no emission is observed for the alternate bonding mode of each complex.     

Evidence for static quenching of MLCT excited states by iodide

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(deeb)(bpy)(2)(PF(6))(2) [where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine] in acetonitrile or dichloromethane were found to be quenched by iodide at room temperature. The ionic strength dependence of the optical spectra gave evidence for ion pairing. Iodide is found to quench the photoluminescence (PL) intensity and influence the spectral distribution of the emitted light. A static component to the time-resolved PL quenching provided further evidence for ground-state adduct. Stern-Volmer analysis of the static component provided an estimate of the iodide-Ru(deeb)(bpy)(2)(2+) adduct equilibrium constant in dichloromethane, K(sv) = 40,000 M(-)(1). Transient absorption studies clearly demonstrate that an electron-transfer quenching mechanism is operative and that I(2)(-)(*) can be photoproduced in high yield, phi = 0.25. For Ru(bpy)(3)(PF(6))(2) in acetonitrile, similar behavior could be observed at iodide concentrations >100 times that required for dichloromethane.     

Formation of assemblies comprising Ru-polypyridine complexes and CdSe nanocrystals studied by ATR-FTIR spectroscopy and DFT modeling

The interaction between CdSe nanocrystals (NCs) passivated with trioctylphosphine oxide (TOPO) ligands and a series of Ru-polypyridine complexes-[Ru(bpy)(3)](PF(6))(2) (1), [Ru(bpy)(2)(mcb)](PF(6))(2) (2), [Ru(bpy)(mcb)(2)](BarF)(2) (3), and [Ru(tpby)(2)(dcb)](PF(6))(2) (4) (where bpy = 2,2'-bipyridine, mcb = 4-carboxy-4'-methyl-2,2'-bipyridine, tbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; dcb = 4,4'-dicarboxy-2,2'-bipyridine, and BarF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)-was studied by attenuated total reflectance FTIR (ATR-FTIR) and modeled using density functional theory (DFT). ATR-FTIR studies reveal that when the solid film of NCs is exposed to an acetonitrile solution of 2, 3, or 4, the complexes chemically bind to the NC surface through their carboxylic acid groups, replacing TOPO ligands. The corresponding spectral changes are observed on a time scale of minutes. In the case of 2, the FTIR spectral changes clearly show that the complex adsorption is associated with a loss of proton from the carboxylic acid group. In the case of 3 and 4, deprotonation of the anchoring group is also detected, while the second, "spectrator" carboxylic acid group remains protonated. The observed energy difference between the symmetric, ν(s), and asymmetric, ν(as), stretch of the deprotonated carboxylic acid group suggests that the complexes are bound to the NC surface via a bridging mode. The results of DFT modeling are consistent with the experiment, showing that for the deprotonated carboxylic acid group the coupling to two Cd atoms via a bridging mode is the energetically most favorable mode of attachment for all nonequivalent NC surface sites and that the attachment of the protonated carboxylic acid is thermodynamically significantly less favorable.     

Static and dynamic quenching of Ru(II) polypyridyl excited states by iodide

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF(6))(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59 700 M(-1). Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I(2)(*)(-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF(6))(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH(2)Cl(2), and light excitation gave a higher I(2)(*)(-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.     

Synthesis, structure, spectroscopic properties, and electrochemical oxidation of ruthenium(II) complexes Incorporating monocarboxylate bipyridine ligands

[Ru(bpy)(2)(Mebpy-COOH)](PF(6))(2).3H(2)O (1), [Ru(phen)(2)(Mebpy-COOH)](ClO(4))(2).5H(2)O (2), [Ru(dppz)(2)(Mebpy-COOH)]Cl(2).9H(2)O (3), and [Ru(bpy)(dppz)(Mebpy-COOH)](PF(6))(2).5H(2)O (4) (bpy = 2,2'-bipyridine, Mebpy-COOH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid, phen = 1,10-phenanthroline, dppz = dipyrido[3,2,-a;2',3-c]phenazine) have been synthesized and characterized spectroscopically and by microanalysis. The [Ru(Mebpy-COOH)(CO)(2)Cl(2)].H(2)O intermediate was prepared by reaction of the monocarboxylic acid ligand, Mebpy-COOH, with [Ru(CO)(2)Cl(2)](n), and the product was then reacted with either bpy, phen, or dppz in the presence of an excess of trimethylamine-N-oxide (Me(3)NO), as the decarbonylation agent, to generate 1, 2, and 3, respectively. For compound 4, [Ru(bpy)(CO)Cl(2)](2) was reacted with Mebpy-COOH to yield [Ru(bpy)(Mebpy-COOH)(CO)Cl](PF(6)).H(2)O as a mixture of two main geometric isomers. Chemical decarbonylation in the presence of dppz gave 4 also as a mixture of two isomers. Electrochemical and spectrophotometric studies indicated that complexes 1 and 2 were present as a mixture of protonated and deprotonated forms in acetonitrile solution because of water of solvation in the isolated solid products. The X-ray crystal structure determination on crystals of [Ru(bpy)2(MebpyCOO)][Ru(bpy)(2)(MebpyCOOH)](3)(PF(6))(7), 1a, and [Ru(phen)(2)(MebpyCOO)](ClO(4)).6H(2)O, 2a, obtained from solutions of 1 and 2, respectively, revealed that 1a consisted of a mixture of protonated and deprotonated forms of the complex in a 1:3 ratio and that 2a consisted of the deprotonated derivative of 2. A distorted octahedral geometry for the Ru(II) centers was found for both complexes. Upon excitation at 450 nm, MeCN solutions of the protonated complexes 1-4 were found to exhibit emission bands in the 635-655 nm range, whereas the corresponding emission maxima of their deprotonated forms were observed at lower wavelengths. Protonation/deprotonation effects were also observed in the luminescence and electrochemical behavior of complexes 1-4. Comprehensive electrochemical studies in acetonitrile show that the ruthenium centers on 1, 2, 3, and 4 are oxidized from Ru(II) to Ru(III) with reversible potentials at 917, 929, 1052, and 1005 mV vs Fc(0/+) (Fc = ferrocene), respectively. Complexes 1 and 2 also exhibit an irreversible oxidation process in acetonitrile, and all compounds undergo ligand-based reduction processes.     

A donor--acceptor--donor bridging ligand in a class III mixed-valence complex

The novel mononuclear and dinuclear complexes [Ru(trpy)(bpy)(apc)][PF(6)] and [(Ru(trpy)(bpy))(2)(mu-adpc)][PF(6)](2) (bpy = 2,2'-bipyridine, trpy = 2,2':6',2' '-terpyridine, apc(-) = 4-azo(phenylcyanamido)benzene, and adpc(2)(-) = 4,4'-azodi(phenylcyanamido)) were synthesized and characterized by (1)H NMR, UV-vis, and cyclic voltammetry. Crystallography showed that the dinuclear Ru(II) complex crystallizes from diethyl ether/acetonitrile solution as [(Ru(trpy)(bpy))(2)(mu-adpc)][PF(6)](2).2(acetonitrile).2(diethyl ether). Crystal structure data are as follows: crystal system triclinic, space group P1, with a, b, and c = 12.480(2), 13.090(3) and 14.147(3) A, respectively, alpha, beta, and gamma = 79.792(3), 68.027(3), and 64.447(3) degrees, respectively, V = 1933.3(6) A(3), and Z = 1. The structure was refined to a final R factor of 0.0421. The mixed-valence complex with metal ions, separated by a through-space distance of 19.5 A, is a class III system, having the comproportionation constant K(c) = 1.3 x 10(13) and an intervalence band at 1920 nm (epsilon(max) = 10 000 M(-1) cm(-1)), in dimethylformamide solution. The results of this study strongly suggest that the bridging ligand adpc(2-) can mediate metal-metal coupling through both hole-transfer and electron-transfer superexchange mechanisms.     

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.     

Selective anion sensing by a ruthenium(II)-bipyridyl-functionalized tripodal tris(urea) receptor

A tripodal tris(urea) ligand with 2,2'-bipyridyl (bpy) substituents (L) has been designed and synthesized, which coordinates with three equivalents of Ru(bpy)(2)Cl(2)·2H(2)O, followed by treatment with NH(4)PF(6), to afford the anion receptor [(bpy)(6)Ru(3)L](PF(6))(6) (1). The anion-binding behavior of the ligand L and the Ru(II)-bpy functionalized receptor 1 toward different anions was investigated by (1)H NMR (for L and 1), fluorescence, and UV-vis spectroscopy (for 1). Both compounds showed selective recognition of SO(4)(2-) or H(2)PO(4)(-) ions in the 1:1 binding mode in the NMR studies. The Ru(II) complex 1 displayed the metal-to-ligand charge transfer emission at 600 nm, which was quenched on addition of the sulfate and dihydrogen phosphate ions. Quantitative fluorescence titration experiments were carried out and the stability constants (log K) of the complex 1 with SO(4)(2-) and H(2)PO(4)(-) ions were obtained to be 4.73 and 4.69 M(-1) (1:1 binding mode), respectively.     

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.     

Characterization of a stable ruthenium complex with an oxyl radical

The ruthenium oxyl radical complex, [Ru(II)(trpy)(Bu(2)SQ)O(.-)] (trpy = 2,2':6',2"-terpyridine, Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) was prepared for the first time by the double deprotonation of the aqua ligand of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2) is reversibly converted to [Ru(III)(trpy)(Bu(2)SQ)(OH-)](+) upon dissociation of the aqua proton (pK(a) 5.5). Deprotonation of the hydroxo proton gave rise to intramolecular electron transfer from the resultant O(2-) to Ru-dioxolene. The resultant [Ru(II)(trpy)(Bu(2)SQ)O(.-)] showed antiferromagnetic behavior with a Ru(II)-semiquinone moiety and oxyl radical, the latter of which was characterized by a spin trapping technique. The most characteristic structural feature of [Ru(II)(trpy)(Bu(2)SQ)O(.-)] is a long Ru-O bond length (2.042(6) A) as the first terminal metal-O bond with a single bond length. To elucidate the substituent effect of a quinone ligand, [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) (4ClSQ = 4-chloro-1,2-benzosemiquinone) was prepared and we compared the deprotonation behavior of the aqua ligand with that of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). Deprotonation of the aqua ligand of [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) induced intramolecular electron transfer from OH- to the [Ru(III)(4ClSQ)] moiety affording [Ru(II)(trpy)(4ClSQ)(OH.)]+, which then probably changed to [Ru(II)(trpy)(4ClSQ)O(.-)]. The antiferromagnetic interactions (J values) between Ru(II)-semiquinone and the oxyl radical for [Ru(II)(trpy)(Bu(2)SQ)O(.-)] and for [Ru(II)(trpy)(4ClSQ)O(.-)] were 2J = -0.67 cm(-1) and -1.97 cm(-1), respectively.     

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.     

cis-Bis(bipyridine)ruthenium Imidazole Derivatives: A Spectroscopic, Kinetic, and Structural Study

The ruthenium bis(bipyridine) complexes cis-[Ru(bpy)(2)Im(OH(2))](2+), cis-[Ru(bpy)(2)(Im)(2)](2+), cis-[Ru(bpy)(2)(N-Im)(2)](2+), cis-[Ru(dmbpy)(2)Im(OH(2))](2+), cis-[Ru(dmbpy)(2)(N-Im)(OH(2))](2+)(bpy = 2,2'-bipyridine, dmbpy = 4,4'-dimethyl-2,2'-bipyridine, Im = imidazole, N-Im = N-methylimidazole), have been synthesized under ambient conditions in aqueous solution (pH 7). Their electrochemical and spectroscopic properties, absorption, emission, and lifetimes were determined and compared. The substitution kinetics of the cis-[Ru(bpy)(2)Im(OH(2))](2+) complexes show slower rates and have lower affinities for imidazole ligands than the corresponding cis-[Ru(NH(3))(4)Im(OH(2))](2+) complexes. The crystal structures of the monoclinic cis-[Ru(bpy)(2)(Im)(2)](BF(4))(2), space group = P2(1)/a, Z = 4, a = 11.344(1) ?, b = 17.499(3) ?, c = 15.114(3) ?, and beta = 100.17(1) degrees, and triclinic cis-[Ru(bpy)(2)(N-Im)(H(2)O)](CF(3)COO)(2).H(2)O, space group = P&onemacr;, Z = 2, a = 10.432(4) ?, b = 11.995(3) ?, c = 13.912(5) ?, alpha = 87.03(3) degrees, beta = 70.28(3) degrees, and gamma = 71.57(2) degrees, complexes show that these molecules crystallize as complexes of octahedral Ru(II) to two bidentate bipyridine ligands with two imidazole ligands or a water and an N-methylimidazole ligand cis to each other. The importance of these molecules is associated with their frequent use in the modification of proteins at histidine residues and in comparisons of the modified protein derivatives with these small molecule analogs.     

Selective recognition of cyanide anion via formation of multipoint NH and phenyl CH hydrogen bonding with acyclic ruthenium bipyridine imidazole receptors in water

Five imidazole-based anion receptors A-E are designed for cyanide anion recognition via hydrogen bonding interaction in water. Only receptors A [Ru(bpy)(2)(mpipH)](ClO(4))(2) (bpy is bipyridine and mpipH is 2-(4-methylphenyl)-imidazo[4,5-f]-1,10-phenanthroline) and E [Ru(2)(bpy)(4)(mbpibH(2))](ClO(4))(4) (mbpibH(2) is 1,3-bis([1,10]-phenanthroline-[5,6-d]imidazol-2-yl)benzene) selectively recognize CN(-) from OAc(-), F(-), Cl(-), Br(-), I(-), NO(3)(-), HSO(4)(-), ClO(4)(-), H(2)PO(4)(-), HCO(3)(-), N(3)(-), and SCN(-) anions in water (without organic solvent) at physiological conditions via formation of multiple hydrogen bonding interaction with binding constants of K(A(H2O)) = 345 ± 21 and K(E(H2O)) = 878 ± 41, respectively. The detection limits of A and E toward CN(-) in water are 100 and 5 μM, respectively. Receptor E has an appropriate pK(a2)* value (8.75) of N-H proton and a C-shape cavity structure with three-point hydrogen bonding, consisting of two NH and one cooperative phenyl CH hydrogen bonds. Appropriate acidity of N-H proton and multipoint hydrogen bonding are both important in enhancing the selectivity and sensitivity toward CN(-) in water. The phenyl CH···CN(-) hydrogen bonding interaction is observed by the HMBC NMR technique for the first time, which provides an efficient approach to directly probe the binding site of the receptor toward CN(-). Moreover, CN(-) induced emission lifetime change of the receptor has been exploited in water for the first time. The energy-optimized structure of E-CN adduct is also proposed on the basis of theoretical calculations.     

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.     

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.     

Filling gaps in the series of noninnocent hetero-1,3-diene chelate ligands: ruthenium complexes of redox-active α-azocarbonyl and α-azothiocarbonyl ligands RNNC(R')E, E = O or S

The series of 4-center unsaturated chelate ligands A═B-C═D with redox activity to yield (-)A-B═C-D(-) in two steps has been complemented by two new combinations RNNC(R')E, E = O or S, R = R' = Ph. The ligands N-benzoyl-N'-phenyldiazene = L(O), and N-thiobenzoyl-N'-phenyldiazene = L(S), (obtained in situ) form structurally characterized compounds [(acac)(2)Ru(L)], 1 with L = L(O), and 3 with L = L(S), and [(bpy)(2)Ru(L)](PF(6)), 2(PF(6)) with L = L(O), and 4(PF(6)) with L = L(S) (acac(-) = 2,4-pentanedionato; bpy = 2,2'-bipyridine). According to spectroscopy and the N-N distances around 1.35 ? and N-C bond lengths of about 1.33 ?, all complexes involve the monoanionic (radical) ligand form. For 1 and 3, the antiferromagnetic spin-spin coupling with electron transfer-generated Ru(III) leads to diamagnetic ground states of the neutral complexes, whereas the cations 2(+) and 4(+) are EPR-active radical ligand complexes of Ru(II). The complexes are reduced and oxidized in reversible one-electron steps. Electron paramagnetic resonance (EPR) and UV-vis-NIR spectroelectrochemistry in conjunction with time-dependent density functional theory (TD-DFT) calculations allowed us to assign the electronic transitions in the redox series, revealing mostly ligand-centered electron transfer: [(acac)(2)Ru(III)(L(0))](+) ? [(acac)(2)Ru(III)(L(?-))] ? [(acac)(2)Ru(III)(L(2-))](-)/[(acac)(2)Ru(II)(L(?-))](-), and [(bpy)(2)Ru(III)(L(?-))](2+)/[(bpy)(2)Ru(II)(L(0))](2+) ? [(bpy)(2)Ru(II)(L(?-))](+) ? [(bpy)(2)Ru(II)(L(2-))](0). The differences between the O and S containing compounds are rather small in comparison to the effects of the ancillary ligands, acac(-) versus bpy.