Spectroscopic and redox properties of Rh<SUP>III</SUP>Ru<SUP>II</SUP> and Ru<SUP>II</SUP>Ru<SUP>II</SUP> complexes derived from 2,2'-bipyridine, pyrazole-3,5-bis(benzimidazole) and 1,2,4-triazole-3,5-dicarboxylic acid as bridging ligands

The heterovalent heterodinuclear complex [(bpy)2RuII(H2pzbzim)RhIII(bpy)2](ClO4)4&#183; 3H2O (1) and the isovalent homodinuclear complex [(bpy)2RuII(trzdc)RuII(bpy)2](ClO4)&#183;5H2O (2), where H3pzbzim=pyrazole-3,5-bis(benzimidazole), H3trzdc=1,2,4-triazole-3,5-dicarboxylic acid and bpy=2,2'-bipyridine, have been synthesized and spectroscopically characterized. Complex 1 undergoes one electron oxidation at 1.20 V (versus Ag/AgCl) in acetonitrile, while for complex 2, two stepwise oxidations occur at 0.63 and 0.81 V with the comproportionation constant Kc, for the equilibrium RuIIRuII + RuIIIRuIII&#8660;2RuIIRuIII, equal to 1.11&#215;103 at 298 K. The acid dissociation constants of the benzimidazole moieties of complex 1 have been determined in acetonitrile-water (3:2) by spectrophotometric titrations. Both complexes 1 and 2 exhibit luminescence spectra and the quantum yields obtained for methanol-ethanol (1:4) glass (at 77 K) are &#966;=3.1&#215;10-2 for 1 and 3.5 &#215; 10-2 for 2. The heterodinuclear complex [(bpy)2RuII(H2pzbzim)RhIII(bpy)2](ClO4)4&#183; 3H2O and the homodinuclear complex [(bpy)2RuII(trzdc)RuII(bpy)2](ClO4)&#183;5H2O have been synthesized and characterized by their IR, UV-Vis, luminescence and 1H NMR spectra. The redox behavior of the complexes has been studied

Homo- and heterobimetallic complexes of ruthenium(II) and osmium(II) with pyrazole-3,5-dicarboxylic acid and 2,2'-bipyridine as co-ligands. Synthesis, structure, stereochemistry, spectroscopy and redox activities

Mononuclear, homodinuclear and heterodinuclear ruthenium(II) and osmium(II) complexes of composition [(bpy)2Ru(H2pzdc)](ClO4)&#183;3H2O (1), [(bpy)2Os(H2pzdc)](ClO4)&#183;3H2O (2), [(bpy)2Ru(pzdc)Ru(bpy)2](ClO4)&#183;H2O (3), [(bpy)2Os(pzdc)Os(bpy)2](ClO4)&#183;H2O (4) and [(bpy)2Ru(pzdc)Os(bpy)2](ClO4)&#183;H2O (5) have been synthesized with pyrazole-3,5-dicarboxylic acid (H3pzdc) and 2,2'-bipyridine (bpy). Complexes 3-5 isolated solely in the homochiral forms have been characterized by their 1H and {1H---1H} COSY NMR spectra. The crystal structures determined for 3 and 5 have revealed that the two compounds are isostructural and the diruthenium compound 3 is present in the rac(&#923;&#923;/&#916;&#916;) form, while the osmium---ruthenium compound 5 is present as the enantiomeric pair (&#923;&#923; and &#916;&#916;). The metal-centered oxidation and bipyridine-centred reduction in 1-5 take place reversibly. As compared with the diruthenium complex 3, the stepwise oxidation of the metal centers in the diosmium complex 4 take place at less positive potentials by 0.45 V. The equilibrium constants for the comproportionation reaction MIIMII+MIIIMIII&#8660;2MIIMIII are found to be almost equal (ca. 6&#215;102) for the diruthenium and diosmium species. From pH-dependent redox potential measurements the acid dissociation constants for the mononuclear complexes 1 and 2 have been determined. The luminescence spectral behavior of the complexes have been investigated in methanol-ethanol (1:4) solution (at 300 K) and in glassy state (77 K) and the quantum yields for the ruthenium(II) complexes are reported

Mononuclear and binuclear ruthenium(II) complexes containing 2,2'-bipyridine or 1,10-phenanthroline and pyrazole-3,5-bis(benzimidazole). Synthesis, structure, isomerism, spectroscopy, and proton-coupled redox activity

A number of mixed-ligand mononuclear and binuclear ruthenium(II) complexes of composition [(bpy)2Ru(H3pzbzim)](ClO4)2&#183;2H2O (1), [(phen)2Ru(H3pzbzim)](ClO4)2&#183;3H2O (2), [(bpy)2Ru(H2pzbzim)Ru(bpy)2](ClO4)3&#183;5H2O (3), [(phen)2Ru(H2pzbzim)Ru(phen)2](ClO4)3&#183;4H2O (4), [(bpy)2Ru(H2pzbzim)Ru(phen)2](ClO4)3&#183;4H2O (5), [(bpy)2Ru(pzbzim)Ru(bpy)2](ClO4)&#183;3H2O (6), and [(phen)2Ru(pzbzim)Ru(phen)2](ClO4)&#183;2H2O (7), where H3pzbzim = pyrazole-3,5-bis(benzimidazole), bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline, have been prepared and characterized. Complexes 3-5 isolated as mixtures of diastereoisomers have been separated by fractional recrystallization. In the cases of 3 and 4, the meso (&#923;&#916;) and racemate (rac) (&#923;&#923;, &#916;&#916;) forms, and for 5, two enantiomeric pairs [(&#923;&#916;, &#916;&#923;) and (&#923;&#923;, &#916;&#916;)] have been obtained. These, as well as the meso and rac diastereoisomers of 6, have been characterized by 1H and 13C NMR spectroscopy. The crystal structure of the meso (&#923;&#916;) form of 3 (C57H53N14Cl3O17Ru2) has been determined, which crystallizes in the monoclinic space group P21/c with a = 11.672(2) &#197;, b = 41.696(9) &#197;, c = 12.871(2) &#197;, &#946; = 90.03(2)&#176;, and Z = 4. The acid-base and redox chemistry of the binuclear complexes has been studied over the pH range 1-12 in acetonitrile-water (3:2) medium. The equilibrium constants of the species involving protonation and deprotonation of the benzimidazole NH protons and the metal oxidation states covering +2 and +3 have been evaluated by spectrophotometric and cyclic voltammetric measurements. During spectrophotometric titrations of the complexes with cerium(IV), the metal-to-ligand charge transfer transitions are replaced by the newly generated ligand-to-metal charge transfer transition. The luminescence spectra of the complexes in solution (at 298 K) and in frozen glass (at 77 K) and their quantum yields have been reported. In contrast to the luminescent behavior of 1-5, corresponding deprotonated compounds do not fluoresce even at 77 K

Synthesis, structure, redox activity and spectroscopic properties of ruthenium(II) complexes with 3,5-bis(benzothiazol-2-yl)pyrazole, 3,5-bis(benzimidazol-2-yl)pyrazole and 2,2'-bipyridine as co-ligands

Ruthenium(II) complexes of composition [(bipy)2Ru(Hpzbzth)][ClO4]2·3H2O 1, [(bipy)2Ru(pzbzth)][ClO4]·2H2O 2, [(bipy)2Ru(pzbzth)Ru(bipy)2][ClO4]3·H2O 3, [(bipy)2Ru(H3pzbzim)][ClO4]2·2H2O 4 and [(bipy)2Ru(Hpzbzim)]·2H2O 5, where Hpzbzth = 3,5-bis(benzthiazol-2-yl)pyrazole, H3pzbzim = 3,5-bis(benzimidazol-2-yl)pyrazole and bipy = 2,2'-bipyridine, have been synthesized and characterized. The crystal structure of 3, in which the two metal centres are bridged by the pyrazolate moiety of the pzbzth anion, has been determined. The two RuN6 chromophores in this complex are separated by 4.723(3) Å. From the significant down-field shift of the pyrazolate CH proton in 3 (8.92 ppm) with respect to 1 (7.78 ppm) and 4 (7.82 ppm), the involvement of S···H(C)···S type interaction in 3 has been proposed. The equilibrium constants of the species involving dissociation of the NH protons of the bridging ligand and the change in the oxidation state of ruthenium from +2 to +3 have been determined in acetonitrile-water (3:2) by cyclic voltammetric and spectrophotometric methods. Redox titrations of complexes 1, 3 and 4 by cerium(IV) have revealed that the disappearence of the metal-to-ligand charge transfer band is accompanied by the appearence of the ligand-to-metal charge transfer band at higher wavelengths. In the case of 3, when 1 equivalent of cerium(IV) is added, the mixed-valence RuIIRuIII species is generated which exhibits an absorption maximum at 950 nm due to the intervalence-transfer transition. The luminescence spectral behaviour of complexes 1-4 has been examined in methanol-ethanol (1:4) solution (at 300 K) as well as in glassy state (at 77 K)

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2'-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2'-bipyridine of composition [(bpy)2Ru(pzdc)Ru(bpy)2](ClO4)&#183;H2O (1) and [(bpy)2Os(pzdc)Os(bpy)2](ClO4)&#183;H2O (2) have been obtained in high yield and have been separated to their homochiral (&#923;&#923;/&#916;&#916;) rac (1a, 2a) and heterochiral (&#923;&#916;/&#916;&#923;) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D 1H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)2Os(pzdc)Os(bpy)2](ClO4)&#183;H2O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case. Dinuclear ruthenium(II) and osmium(II) complexes [(bpy)2M(pzdc)M(bpy)2](ClO4) &#183; H2O containing 2,2'-bipyridine and pyrazole-3,5-dicarboxylate(pzdc3-) as the bridging ligand have been separated to their homochiral (&#923;&#923;/&#916;&#916;) rac and heterochiral (&#923;&#916;/&#916;&#923;) meso forms. The physicochemical properties of the diastereoisomers have been compared by 1H NMR, electronic spectroscopies and electrochemistry. The structure of the rac form of the diosmium(II) complex cation is shown

Synthesis, spectroscopic properties and proton-coupled redox activities of mononuclear osmium(II) mixed-chelates derived from pyrazole-3,5-bis(benzimidazole) and 2,2'-bipyridine

The mixed-ligand osmium(II) complexes [(bpy)<SUB>2</SUB>Os(H<SUB>3</SUB>pzbzim)](ClO<SUB>4</SUB>)<SUB>2</SUB>·2H<SUB>2</SUB>O (1) and [(bpy)<SUB>2</SUB>Os(Hpzbzim)]·2H<SUB>2</SUB>O (2), where H<SUB>3</SUB>pzbzim=pyrazole-3,5-bis(benzimidazole) and bpy=2,2'-bipyridine, have been synthesized and spectroscopically characterized. In complex (2), the NH deprotonation occurs at the pyrazole and at one of the metal-bound benzimidazole sites. As compared to complex (1), which undergoes reversible oxidation at 0.48 V (vs. Ag/AgCl) in acetonitrile, the redox potential of (2) is shifted to a much lower value, 0.14 V. The proton-coupled redox activities of the complexes have been studied over the pH range 1-12 in acetonitrile-water (3:2). From the pH versus E<SUB>1/2</SUB> profile, the equilibrium constants of the complex species in the protonated/deprotonated forms and the metal ion in +2/+3 oxidation states have been determined. The pK<SUB>a</SUB> values of the complexes in the +2 state have also been determined spectrophotometrically. The spectrophotometric titration of complex (1) with cerium(IV) has revealed the disappearance of the more intense and higher energy Os<SUP>II</SUP>dΠ→Π<SUP>∗</SUP>(bpy) MLCT band and the appearance of the less intense and lower energy Π(H<SUB>3</SUB>pzbzim)→Os<SUP>III</SUP>dΠ LMCT band. The luminescence spectrum of (1) in methanol-ethanol at 77 K has shown it to be a weak emitter, while no emission is observed for (2)

Osmium(II) mixed-chelate derived from imidazole 4,5-bis(benzimidazole) and 2,2'-bipyridine as multichannel sensor for anions: Synthesis, structural characterization and binding studies

1418-1428Mixed-ligand complex of composition [(bpy)2Os(H3Imbzim)](ClO4)2∙2H2O (1), where H3Imbzim = 4,5-bis(benzimidazole-2-yl)imidazole and bpy = 2,2¢-bipyridine, has been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structure of the complex has been determined which showed that it crystallized in triclinic form with the space group P-1. The anion binding properties of the complex has been thoroughly investigated in solution using absorption, emission, and 1H NMR spectral measurements. The metalloreceptor acts as sensor for F-, AcO-, and to some extent for H2PO4- anions. Although at relatively lower concentration of anions the 1:1 H-bonded adduct is formed, in the presence of excess of anions deprotonation of the imidazole N–H fragments occurs which is accompanied by a distinct change of color. Double deprotonation is also observed in the presence of hydroxide. The binding affinities of different anions towards the receptors have been evaluated. Cyclic voltammetry measurements carried out in acetonitrile have provided evidence in favor of an anion-dependent electrochemical response of the receptor with F- and AcO- ions

A correlation involving 1H NMR spectra and exchange coupling constants of a family of phenoxo-bridged macrocyclic dicopper(II) complexes

The 1H NMR spectra of eleven macrocyclic tetraiminodiphenolate dicopper(II) complexes derived from 4-methyl (or tert-butyl)-2,6-diformyl/diacetyl/dibutyrylphenols and linker diamines such as 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane or 1,2-diaminobenzene have been studied in (CD3)2SO at 25 °C. The hyperfine-shifted 1H NMR signals have been assigned from their measured longitudinal relaxation times (T1) and peak areas. The two copper(II) centres in these compounds are strongly antiferromagnetically coupled with the exchange coupling constant -2J (H = -2JS1·S2) lying between 690 and 860 cm-1. It is shown that a plot of the chemical shift (d) due to the phenolate ring protons of the macrocycles at 298 K s. the exchange coupling constant (-2J) of the corresponding complexes provides a smooth sigmoidal curve that can be simulated by the expression -2J = 220.6 [1 + exp{(δ - 4.12)/2.93}]-1 + 667

Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)–Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units

We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru­(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0–158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σp parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans–trans to trans–cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans–cis to trans–trans forms was also achieved on interacting with visible light. Change from trans–trans to the corresponding trans–cis form leads to emission quenching, whereas trans–cis to the corresponding trans–trans form leads to restoration of emission. In essence, “on–off” and “off–on” photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands

Iso- and mixed-valent phenoxy bridged binuclear macrocyclic complexes of cobalt, iron and manganese

The binuclear complexes of a tetraaminodiphenol macrocyclic ligand (H2L) of cobalt(II) and manganese(II) with the composition [M2LX2]&#946;H2O (X = Cl or Br) and of iron(II) with the composition [Fe2L(imidazole)2(CH3OH)2](ClO4)2&#183;2CH3OH have been synthesized and spectroscopically characterized. Cyclic voltammetric measurements of the dicobalt(II) complexes have indicated that the generation of CoIII-CoII and CoIII-CoIII species take place quasi-reversibly or irreversibly at about 0.38 and 0.90 V vs SCE, respectively. The dimanganese(II) complexes undergo quasi-reversible one-electron oxidation at about 0.32 V, but further oxidation does not occur up to 1.2 V. The iron(II) complex irreversibly gets oxidized at ca 1 V. The dicobalt(II) and dimanganese(II) complexes can be oxidized with bromine and the mixed-valence complexes [MIIIMIILCl2Br(CH3OH)]&#183;solvent have been isolated. Variable-temperature magnetic measurements of [CoIIICoIILCl2Br (CH3OH)]&#183;0.5CH2Cl2, [Mn2IILBr2(CH3OH)2]&#183;H2O and [Fe2IIL(imidazole)2(CH3OH)2] (ClO4)2&#183;2CH3OH have indicated that the mixed-valence cobalt complex behaves as a S = 3/2 system, while both the diiron(II) and dimanganese(II) complexes exhibit antiferromagnetic exchange coupling with J =-6.3 and -6.1 cm-1, respectively