Wesley Browne - Academia.edu (original) (raw)
Papers by Wesley Browne
Inorganic Chemistry, Sep 1, 2002
A systematic approach to the deuteriation of polypyridyl type ligands is reported. A range of iso... more A systematic approach to the deuteriation of polypyridyl type ligands is reported. A range of isotopologues of heteroaromatic compounds containing pyrazyl, pyridyl, 1,2,4-triazole, thienyl, methyl, and phenyl moieties, have been prepared in a cost-effective manner, using a range of methods based on subcritical aqueous media. Selectively and fully deuteriated ligands are characterized by mass spectrometry and 1 H, 2 D, and 13 C NMR spectroscopy. The application of deuteriation to supramolecular chemistry is discussed. a In the case of partially deuteriated compounds, exchange at individual positions is given in parentheses. b E in 20 mL of H2O at 200°C; F 0.1 g of 10% Pd/C in 20 mL of H2O at 200°C; # indicates preparation from perdeuteriated reagents (see Experimental Section). For other reaction conditions, see . c On the basis of recovered yield, § indicates that when species reacted for 30 days, no further exchange was observed. For 12b-g, see Scheme 2 for further information.
Journal of the Chinese Chemical Society, 2007
The synthesis, spectroscopic, electrochemical and photophysical characterization of a series of d... more The synthesis, spectroscopic, electrochemical and photophysical characterization of a series of dinuclear ruthenium(II) complexes of the type [(bpy) 2 Ru(NnN) 2 RuCl(bpy) 2 ](PF 6 ) 3 , where NnN = 4,4¢bipyridyl (N0N), 1,2-bis(4-pyridyl)ethylene (NEN), 1,2-bis(4-pyridyl)ethane (N2N), and 4,4¢-trimethylenedipyridine (N3N) are reported. The photophysical and electrochemical properties are discussed with particular emphasis on the ability of the bridging ligands to support intercomponent interaction. Fig. 1. Structures of NnN type bridging ligands discussed in the text.
Inorganic Chemistry, 2016
The photocatalytic generation of hydrogen (H2) from protons by two cyclometalated ruthenium-plati... more The photocatalytic generation of hydrogen (H2) from protons by two cyclometalated ruthenium-platinum polypyridyl complexes, [Ru(bpy)2(2,5-bpp)PtIS](2+) (1) and [Ru(dceb)2(2,5-bpp)PtIS](2+) (2) [where bpy = 2,2'-bipyridine, 2,5-bpp = 2,2',5',2″-terpyridine, dceb = 4,4'-di(carboxyethyl)bipyridine, and S = solvent], is reported. Turnover numbers (TONs) for H2 generation were increased by nearly an order of magnitude by the introduction of carboxyethyl ester units, i.e., from 80 for 1P to 650 for 2P after 6 h of irradiation, with an early turnover frequency (TOF) increasing from 15 to 200 h(-1). The TON and TOF values for 2P are among the highest reported to date for supramolecular photocatalysts. The increase correlates with stabilization of the excited states localized on the peripheral ligands of the light-harvesting Ru(II) center.
Inorg Chem, 2004
A series of homo-and heteronuclear ruthenium and osmium polypyridyl complexes with the bridging l... more A series of homo-and heteronuclear ruthenium and osmium polypyridyl complexes with the bridging ligands 1,3bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H 2 mL) and 1,4-bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H 2 pL) are reported. The photophysical properties of these compounds are investigated, and particular attention is paid to the heteronuclear (RuOs) compounds, which exhibit dual emission. This is in contrast to phenyl-bridged polypyridine Ru−Os complexes with a similar metal−metal distance, in which the Ru emission is strongly quenched because the nature of the bridging ligand allows for an efficient through-bond coupling. The results obtained for the compounds reported here suggest that energy transfer is predominantly taking place via a dipole−dipole, Förster type, mechanism, that may dominate when through-bond coupling is weak. This is in stark contrast to ground state interaction, which is found to be critically dependent on the nature of the bridging unit employed. Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Ventura, M. Coord. Chem. ReV. 1994, 132, 1. (d) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. ReV. 1996, 96, 759. (e) Slate, C. A.; Striplin, D. R.; Moss, J. A.; Chen, P.; Erickson, B. W.; Meyer, T. J. Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Bargelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993. (h) Carraway, E. R.; Demas, J. N.; DeGraff, B. A.
Inorganic Chemistry, 2006
The syntheses and spectroscopic characterization of two 1,2,4-triazole-based oxovanadium(V) compl... more The syntheses and spectroscopic characterization of two 1,2,4-triazole-based oxovanadium(V) complexes are reported: 1- [VO2L1]- and 2 [(VOL2)2(OMe)2] (where H2L1 = 3-(2'-hydroxyphenyl)-5-(pyridin-2' '-yl)-1H-1,2,4-triazole, H3L2 = bis-3,5-(2'-hydroxyphenyl)-1H-1,2,4-triazole). The ligand environment (N,N,O vs O,N,O) is found to have a profound influence on the properties and reactivity of the complexes formed. The presence of the triazolato ligand allows for pH tuning of the spectroscopic and electrochemical properties, as well as the interaction and stability of the complexes in the presence of hydrogen peroxide. The vanadium(IV) oxidation states were generated electrochemically and characterized by UV-vis and EPR spectroscopies. For 2, under acidic conditions, rapid exchange of the methoxide ligands with solvent [in particular, in the vanadium(IV) redox state] was observed.
ABSTRACT We report the application of multi-wavelength resonance Raman (rR) spectroscopy for the ... more ABSTRACT We report the application of multi-wavelength resonance Raman (rR) spectroscopy for the characterisation of vinyl-bridged polysexithiophene films formed by electropolymerisation on gold electrodes. Resonance Raman spectroscopy of the neutral, polaronic and bipolaronic states of the polymer were determined by in situ [small mu ]Raman spectroelectrochemistry. In particular the differences in the UV/Vis-NIR absorption spectra of the neutral, monopolaronic and bipolaronic states of the polymer allow for characterising the redox state of the polymer films in PDMS based microfluidic channels. The information obtained in this way allows for determination of the optimum film thickness required for achieving full electrochemical switching between neutral and charged states, which is important in their use in switching surface properties. The approach taken allows for direct analysis of polymer films formed within microchannels.
Browne Wesley R and Weldon Frances and Guckian Adrian L and Vos Johannes G Modulation of Internuclear Communication in Multinuclear Ruthenium Polypyridyl Complexes Collection of Czechoslovak Chemical Communications 68 P 1467 Issn 0010 0765, 2003
The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl... more The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl complexes based on the bridging ligands 1,3-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 1,4-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 2,5-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]thiophene, 2,5-bis-[5-pyrazinyl-1H-1,2,4-triazol-3-yl]thiophene are reported. Electrochemical studies indicate that in these systems, the ground state interaction is critically dependent on the nature of the bridging ligand and its protonation state, with strong and weak interactions being observed for thiophene-and phenylene-bridged complexes, respectively.
Journal of the American Chemical Society, Jan 28, 2003
Because of their favorable photophysical properties, ruthenium-(II) polypyridine complexes are pl... more Because of their favorable photophysical properties, ruthenium-(II) polypyridine complexes are playing a key role in the development of multicomponent (supramolecular) systems capable of performing useful photo-or redox-triggered functions such as charge 1 and information storage. 2 These compounds emit from a long-lived triplet metal-to-ligand charge-transfer state ( 3 MLCT) that is populated from higher-energy excited states. The photophysical behavior of the emitting triplet state is well understood, 1-6 but much less is known about the events that lead to its formation. The observation that, in nanocrystalline TiO 2 solar cells modified with monolayers of a ruthenium complex, the electron injection from the excited dye into the TiO 2 is subpicosecond has led to a sharp increase in the interest in the parameters that control the formation of the triplet state. Issues of interest are the lifetime of the lowest singlet state/s and the efficiency of the intersystem crossing (ISC) process that leads to population of the triplet state.
Inorganic chemistry, Jan 5, 2015
The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II... more The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II)(CH3CN)2](OTf)2 (1) ((Me,H)PyTACN = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = CF3SO3) is described together with its reactivity with NaOCl. 1 catalyzes the chlorination of alkanes with NaOCl, producing only a trace amount of oxygenated byproducts. The reaction was monitored spectroscopically and by high resolution electrospray-mass spectrometry (ESI-MS) with the aim to elucidate mechanistic aspects. NaOCl reacts with 1 in acetonitrile to form the transient species [(L)Ni(II)-OCl(S)](+) (A) (L = (Me,H)PyTACN, S = solvent), which was identified by ESI-MS. UV/vis absorption, electron paramagnetic resonance, and resonance Raman spectroscopy indicate that intermediate A decays to the complex [(L)Ni(III)-OH(S)](2+) (B) presumably through homolytic cleavage of the O-Cl bond, which liberates a Cl(•) atom. Hydrolysis of acetonitrile to acetic acid under the applied conditio...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 25, 2015
Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped ... more Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a Ni(II) precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., CH bonds, CC bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic OO bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a Ni(III) -oxyl compound.
Inorganic Chemistry, 2015
Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-Nbis(2... more Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-Nbis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L 1 ) and [N-bis(1methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L 2 ), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolylcontaining arms. The complexes [Fe II (CH 3 CN)(L)] 2+ (L = L 1 (1); L 2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe IV (O)(L)] 2+ (L = L 1 (3); L 2 (4)), which were characterized by UV−vis spectroscopy, high resolution mass spectrometry, and Mossbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L 1 ) and 2.5 h (L = L 2 ). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe IV (O)(N4Py)] 2+ ), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe IV (O)(L 2 )] 2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C−H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
omitted inadvertently. In their 1999 report, these authors reported a transient process with a 5 ... more omitted inadvertently. In their 1999 report, these authors reported a transient process with a 5 ps time constant in the femtosecond transient absorption (TA) spectroscopy of [Ru(dmb) 3 ] 2+ (where dmb ) 4,4′-dimethyl-2,2′-bipyridyl). This process was assigned to vibrational cooling dynamics of the 3 MLCT manifold (where MLCT ) metal to ligand charge transfer). The authors noted
European Journal of Inorganic Chemistry, 2015
ABSTRACT The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(μ-O)3(tm... more ABSTRACT The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(μ-O)3(tmtacn)2]2+ (1; tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis(carboxylato) complexes of the type [MnIII2(μ-O)(μ-RCO2)2(tmtacn)2]2+. The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of μ-oxido ligands for μ-carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster.
Faraday Discuss., 2015
A series of supramolecular assemblies of the type [Ru(L-L)2(L&amp... more A series of supramolecular assemblies of the type [Ru(L-L)2(L'-L)MX2)](n+) are reported where L-L is 2,2'-bipyridine (bipy), 4,4'-di-tetra-butyl-bipyridine (tbbipy) or 4,4'-diethoxycarbonyl-2,2'-bipyridine (dceb), L-L' is tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz), 2,2':5',2''-terpyridine (2,5-bpp), 2,2':6',2''-terpyridine, (2,6-bpp), 2,5-di(pyridine-2-yl)pyrazine (2,5-dpp) or 2,3-di(pyridine-2-yl)pyrazine (2,3-dpp), and MX2 is PdCl2, PtCl2 or PtI2. The photocatalytic behaviour with respect to hydrogen generation of these compounds and their ultrafast photophysical properties are discussed as a function of the nature of the peripheral ligands, the bridging ligands and the catalytic centre. The results obtained show how differences in the chemical composition of the photocatalysts can affect intramolecular photoinduced electron transfer processes and the overall photocatalytic efficiency.
Inorganica Chimica Acta, 2015
Bis-r-(phenyl)-tetrakis-l-(capralactamato)dirhodium(III), formed by oxidative reactions of dirhod... more Bis-r-(phenyl)-tetrakis-l-(capralactamato)dirhodium(III), formed by oxidative reactions of dirhodium(II) carboxamidates with arylboronic acids promoted by copper(II), exists in two non-interconvertable conformations. In these conformational isomers the caprolactamate ligands are oriented around dirhodium(III) as a propeller with apparent C4 symmetry and in a biplanar array. Cyclic voltammetry and spectroelectrochemistry as well as Raman and resonance Raman spectroscopy of the conformationally distinct Rh 2 6+ carboxamidates have been obtained in order to explore the origin of their non-interconversion. Differences in their vibrational spectra occur only in the low wavenumber spectral region, but there is a 250 mV difference in oxidation potential between conformational isomers consistent with a substantial difference ground state energies. Notably, spectroelectrochemical data show that oxidation does not result in isomerization.
Dalton transactions (Cambridge, England : 2003), Jan 28, 2015
The interaction between salmon testes DNA (st-DNA) and a series of Cu(II) polypyridyl complexes, ... more The interaction between salmon testes DNA (st-DNA) and a series of Cu(II) polypyridyl complexes, i.e. [Cu(dmbpy)(NO3)2] (1) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), [Cu(bpy)(NO3)2] (2) (bpy = 2,2'-bipyridine), [Cu(phen)(NO3)2] (3) (phen = phenanthroline), [Cu(terpy)(NO3)2]·H2O (4) (terpy = 2,2':6',2″-terpyridine), [Cu(dpq)(NO3)2] (5) (dpq = dipyrido-[3,2-d:2',3'-f]-quinoxaline) and [Cu(dppz)(NO3)2] (6) (dppz = dipyrido[3,2-a:2',3'-c]phenazine) was studied by UV/Vis absorption, Circular Dichroism, Linear Dichroism, EPR, Raman and (UV and vis) resonance Raman spectroscopies and viscometry. These complexes catalyse enantioselective C-C bond forming reactions in water with DNA as the source of chirality. Complex 1 crystallizes as an inorganic polymer with nitrate ligands bridging the copper ions, which adopt essentially a distorted square pyramidal structure with a fifth bridging nitrate ligand at the axial position. Raman spectroscopy indicates that ...
Dalton transactions (Cambridge, England : 2003), Jan 21, 2014
The detection of nuclear radiation necessitates the availability of new generations of tunable bl... more The detection of nuclear radiation necessitates the availability of new generations of tunable blue emitting fluorophores with high emission quantum yields. Here we show that pyridyl-1,2,4-triazole based diphenyl boron complexes can provide highly tuneable emission through facile modification of the C5 position of the 1,2,4-triazolato ring. The series of complexes prepared show a wide range of emission from near-UV to green, enabling fine control over the spectral overlap with detectors used in scintillator technology.
ChemInform, 2008
Manganese Catalyzed Asymmetric cis-Dihydroxylation with H2O2. -(DE BOER, J. W.; BROWNE, W. R.; HA... more Manganese Catalyzed Asymmetric cis-Dihydroxylation with H2O2. -(DE BOER, J. W.; BROWNE, W. R.; HARUTYUNYAN, S. R.; BINI, L.; TIEMERSMA-WEGMAN, T. D.; ALSTERS, P. L.; HAGE, R.; FERINGA*, B. L.; Chem. Commun. (Cambridge) 2008, 32, 3747-3749; Stratingh Inst. Chem., Univ. Groningen, NL-9747 AG Groningen, Neth.; Eng.) -M. Paetzel 52-142
Inorganic Chemistry, Sep 1, 2002
A systematic approach to the deuteriation of polypyridyl type ligands is reported. A range of iso... more A systematic approach to the deuteriation of polypyridyl type ligands is reported. A range of isotopologues of heteroaromatic compounds containing pyrazyl, pyridyl, 1,2,4-triazole, thienyl, methyl, and phenyl moieties, have been prepared in a cost-effective manner, using a range of methods based on subcritical aqueous media. Selectively and fully deuteriated ligands are characterized by mass spectrometry and 1 H, 2 D, and 13 C NMR spectroscopy. The application of deuteriation to supramolecular chemistry is discussed. a In the case of partially deuteriated compounds, exchange at individual positions is given in parentheses. b E in 20 mL of H2O at 200°C; F 0.1 g of 10% Pd/C in 20 mL of H2O at 200°C; # indicates preparation from perdeuteriated reagents (see Experimental Section). For other reaction conditions, see . c On the basis of recovered yield, § indicates that when species reacted for 30 days, no further exchange was observed. For 12b-g, see Scheme 2 for further information.
Journal of the Chinese Chemical Society, 2007
The synthesis, spectroscopic, electrochemical and photophysical characterization of a series of d... more The synthesis, spectroscopic, electrochemical and photophysical characterization of a series of dinuclear ruthenium(II) complexes of the type [(bpy) 2 Ru(NnN) 2 RuCl(bpy) 2 ](PF 6 ) 3 , where NnN = 4,4¢bipyridyl (N0N), 1,2-bis(4-pyridyl)ethylene (NEN), 1,2-bis(4-pyridyl)ethane (N2N), and 4,4¢-trimethylenedipyridine (N3N) are reported. The photophysical and electrochemical properties are discussed with particular emphasis on the ability of the bridging ligands to support intercomponent interaction. Fig. 1. Structures of NnN type bridging ligands discussed in the text.
Inorganic Chemistry, 2016
The photocatalytic generation of hydrogen (H2) from protons by two cyclometalated ruthenium-plati... more The photocatalytic generation of hydrogen (H2) from protons by two cyclometalated ruthenium-platinum polypyridyl complexes, [Ru(bpy)2(2,5-bpp)PtIS](2+) (1) and [Ru(dceb)2(2,5-bpp)PtIS](2+) (2) [where bpy = 2,2'-bipyridine, 2,5-bpp = 2,2',5',2″-terpyridine, dceb = 4,4'-di(carboxyethyl)bipyridine, and S = solvent], is reported. Turnover numbers (TONs) for H2 generation were increased by nearly an order of magnitude by the introduction of carboxyethyl ester units, i.e., from 80 for 1P to 650 for 2P after 6 h of irradiation, with an early turnover frequency (TOF) increasing from 15 to 200 h(-1). The TON and TOF values for 2P are among the highest reported to date for supramolecular photocatalysts. The increase correlates with stabilization of the excited states localized on the peripheral ligands of the light-harvesting Ru(II) center.
Inorg Chem, 2004
A series of homo-and heteronuclear ruthenium and osmium polypyridyl complexes with the bridging l... more A series of homo-and heteronuclear ruthenium and osmium polypyridyl complexes with the bridging ligands 1,3bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H 2 mL) and 1,4-bis(5-(2-pyridyl)-1H-1,2,4-triazol-3-yl)benzene (H 2 pL) are reported. The photophysical properties of these compounds are investigated, and particular attention is paid to the heteronuclear (RuOs) compounds, which exhibit dual emission. This is in contrast to phenyl-bridged polypyridine Ru−Os complexes with a similar metal−metal distance, in which the Ru emission is strongly quenched because the nature of the bridging ligand allows for an efficient through-bond coupling. The results obtained for the compounds reported here suggest that energy transfer is predominantly taking place via a dipole−dipole, Förster type, mechanism, that may dominate when through-bond coupling is weak. This is in stark contrast to ground state interaction, which is found to be critically dependent on the nature of the bridging unit employed. Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Ventura, M. Coord. Chem. ReV. 1994, 132, 1. (d) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. ReV. 1996, 96, 759. (e) Slate, C. A.; Striplin, D. R.; Moss, J. A.; Chen, P.; Erickson, B. W.; Meyer, T. J. Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Bargelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993. (h) Carraway, E. R.; Demas, J. N.; DeGraff, B. A.
Inorganic Chemistry, 2006
The syntheses and spectroscopic characterization of two 1,2,4-triazole-based oxovanadium(V) compl... more The syntheses and spectroscopic characterization of two 1,2,4-triazole-based oxovanadium(V) complexes are reported: 1- [VO2L1]- and 2 [(VOL2)2(OMe)2] (where H2L1 = 3-(2'-hydroxyphenyl)-5-(pyridin-2' '-yl)-1H-1,2,4-triazole, H3L2 = bis-3,5-(2'-hydroxyphenyl)-1H-1,2,4-triazole). The ligand environment (N,N,O vs O,N,O) is found to have a profound influence on the properties and reactivity of the complexes formed. The presence of the triazolato ligand allows for pH tuning of the spectroscopic and electrochemical properties, as well as the interaction and stability of the complexes in the presence of hydrogen peroxide. The vanadium(IV) oxidation states were generated electrochemically and characterized by UV-vis and EPR spectroscopies. For 2, under acidic conditions, rapid exchange of the methoxide ligands with solvent [in particular, in the vanadium(IV) redox state] was observed.
ABSTRACT We report the application of multi-wavelength resonance Raman (rR) spectroscopy for the ... more ABSTRACT We report the application of multi-wavelength resonance Raman (rR) spectroscopy for the characterisation of vinyl-bridged polysexithiophene films formed by electropolymerisation on gold electrodes. Resonance Raman spectroscopy of the neutral, polaronic and bipolaronic states of the polymer were determined by in situ [small mu ]Raman spectroelectrochemistry. In particular the differences in the UV/Vis-NIR absorption spectra of the neutral, monopolaronic and bipolaronic states of the polymer allow for characterising the redox state of the polymer films in PDMS based microfluidic channels. The information obtained in this way allows for determination of the optimum film thickness required for achieving full electrochemical switching between neutral and charged states, which is important in their use in switching surface properties. The approach taken allows for direct analysis of polymer films formed within microchannels.
Browne Wesley R and Weldon Frances and Guckian Adrian L and Vos Johannes G Modulation of Internuclear Communication in Multinuclear Ruthenium Polypyridyl Complexes Collection of Czechoslovak Chemical Communications 68 P 1467 Issn 0010 0765, 2003
The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl... more The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl complexes based on the bridging ligands 1,3-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 1,4-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 2,5-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]thiophene, 2,5-bis-[5-pyrazinyl-1H-1,2,4-triazol-3-yl]thiophene are reported. Electrochemical studies indicate that in these systems, the ground state interaction is critically dependent on the nature of the bridging ligand and its protonation state, with strong and weak interactions being observed for thiophene-and phenylene-bridged complexes, respectively.
Journal of the American Chemical Society, Jan 28, 2003
Because of their favorable photophysical properties, ruthenium-(II) polypyridine complexes are pl... more Because of their favorable photophysical properties, ruthenium-(II) polypyridine complexes are playing a key role in the development of multicomponent (supramolecular) systems capable of performing useful photo-or redox-triggered functions such as charge 1 and information storage. 2 These compounds emit from a long-lived triplet metal-to-ligand charge-transfer state ( 3 MLCT) that is populated from higher-energy excited states. The photophysical behavior of the emitting triplet state is well understood, 1-6 but much less is known about the events that lead to its formation. The observation that, in nanocrystalline TiO 2 solar cells modified with monolayers of a ruthenium complex, the electron injection from the excited dye into the TiO 2 is subpicosecond has led to a sharp increase in the interest in the parameters that control the formation of the triplet state. Issues of interest are the lifetime of the lowest singlet state/s and the efficiency of the intersystem crossing (ISC) process that leads to population of the triplet state.
Inorganic chemistry, Jan 5, 2015
The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II... more The spectroscopic, electrochemical, and crystallographic characterization of [((Me,H)PyTACN)Ni(II)(CH3CN)2](OTf)2 (1) ((Me,H)PyTACN = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = CF3SO3) is described together with its reactivity with NaOCl. 1 catalyzes the chlorination of alkanes with NaOCl, producing only a trace amount of oxygenated byproducts. The reaction was monitored spectroscopically and by high resolution electrospray-mass spectrometry (ESI-MS) with the aim to elucidate mechanistic aspects. NaOCl reacts with 1 in acetonitrile to form the transient species [(L)Ni(II)-OCl(S)](+) (A) (L = (Me,H)PyTACN, S = solvent), which was identified by ESI-MS. UV/vis absorption, electron paramagnetic resonance, and resonance Raman spectroscopy indicate that intermediate A decays to the complex [(L)Ni(III)-OH(S)](2+) (B) presumably through homolytic cleavage of the O-Cl bond, which liberates a Cl(•) atom. Hydrolysis of acetonitrile to acetic acid under the applied conditio...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 25, 2015
Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped ... more Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a Ni(II) precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., CH bonds, CC bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic OO bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a Ni(III) -oxyl compound.
Inorganic Chemistry, 2015
Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-Nbis(2... more Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-Nbis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L 1 ) and [N-bis(1methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L 2 ), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolylcontaining arms. The complexes [Fe II (CH 3 CN)(L)] 2+ (L = L 1 (1); L 2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe IV (O)(L)] 2+ (L = L 1 (3); L 2 (4)), which were characterized by UV−vis spectroscopy, high resolution mass spectrometry, and Mossbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L 1 ) and 2.5 h (L = L 2 ). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe IV (O)(N4Py)] 2+ ), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe IV (O)(L 2 )] 2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C−H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
omitted inadvertently. In their 1999 report, these authors reported a transient process with a 5 ... more omitted inadvertently. In their 1999 report, these authors reported a transient process with a 5 ps time constant in the femtosecond transient absorption (TA) spectroscopy of [Ru(dmb) 3 ] 2+ (where dmb ) 4,4′-dimethyl-2,2′-bipyridyl). This process was assigned to vibrational cooling dynamics of the 3 MLCT manifold (where MLCT ) metal to ligand charge transfer). The authors noted
European Journal of Inorganic Chemistry, 2015
ABSTRACT The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(μ-O)3(tm... more ABSTRACT The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(μ-O)3(tmtacn)2]2+ (1; tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis(carboxylato) complexes of the type [MnIII2(μ-O)(μ-RCO2)2(tmtacn)2]2+. The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of μ-oxido ligands for μ-carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster.
Faraday Discuss., 2015
A series of supramolecular assemblies of the type [Ru(L-L)2(L&amp... more A series of supramolecular assemblies of the type [Ru(L-L)2(L'-L)MX2)](n+) are reported where L-L is 2,2'-bipyridine (bipy), 4,4'-di-tetra-butyl-bipyridine (tbbipy) or 4,4'-diethoxycarbonyl-2,2'-bipyridine (dceb), L-L' is tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz), 2,2':5',2''-terpyridine (2,5-bpp), 2,2':6',2''-terpyridine, (2,6-bpp), 2,5-di(pyridine-2-yl)pyrazine (2,5-dpp) or 2,3-di(pyridine-2-yl)pyrazine (2,3-dpp), and MX2 is PdCl2, PtCl2 or PtI2. The photocatalytic behaviour with respect to hydrogen generation of these compounds and their ultrafast photophysical properties are discussed as a function of the nature of the peripheral ligands, the bridging ligands and the catalytic centre. The results obtained show how differences in the chemical composition of the photocatalysts can affect intramolecular photoinduced electron transfer processes and the overall photocatalytic efficiency.
Inorganica Chimica Acta, 2015
Bis-r-(phenyl)-tetrakis-l-(capralactamato)dirhodium(III), formed by oxidative reactions of dirhod... more Bis-r-(phenyl)-tetrakis-l-(capralactamato)dirhodium(III), formed by oxidative reactions of dirhodium(II) carboxamidates with arylboronic acids promoted by copper(II), exists in two non-interconvertable conformations. In these conformational isomers the caprolactamate ligands are oriented around dirhodium(III) as a propeller with apparent C4 symmetry and in a biplanar array. Cyclic voltammetry and spectroelectrochemistry as well as Raman and resonance Raman spectroscopy of the conformationally distinct Rh 2 6+ carboxamidates have been obtained in order to explore the origin of their non-interconversion. Differences in their vibrational spectra occur only in the low wavenumber spectral region, but there is a 250 mV difference in oxidation potential between conformational isomers consistent with a substantial difference ground state energies. Notably, spectroelectrochemical data show that oxidation does not result in isomerization.
Dalton transactions (Cambridge, England : 2003), Jan 28, 2015
The interaction between salmon testes DNA (st-DNA) and a series of Cu(II) polypyridyl complexes, ... more The interaction between salmon testes DNA (st-DNA) and a series of Cu(II) polypyridyl complexes, i.e. [Cu(dmbpy)(NO3)2] (1) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), [Cu(bpy)(NO3)2] (2) (bpy = 2,2'-bipyridine), [Cu(phen)(NO3)2] (3) (phen = phenanthroline), [Cu(terpy)(NO3)2]·H2O (4) (terpy = 2,2':6',2″-terpyridine), [Cu(dpq)(NO3)2] (5) (dpq = dipyrido-[3,2-d:2',3'-f]-quinoxaline) and [Cu(dppz)(NO3)2] (6) (dppz = dipyrido[3,2-a:2',3'-c]phenazine) was studied by UV/Vis absorption, Circular Dichroism, Linear Dichroism, EPR, Raman and (UV and vis) resonance Raman spectroscopies and viscometry. These complexes catalyse enantioselective C-C bond forming reactions in water with DNA as the source of chirality. Complex 1 crystallizes as an inorganic polymer with nitrate ligands bridging the copper ions, which adopt essentially a distorted square pyramidal structure with a fifth bridging nitrate ligand at the axial position. Raman spectroscopy indicates that ...
Dalton transactions (Cambridge, England : 2003), Jan 21, 2014
The detection of nuclear radiation necessitates the availability of new generations of tunable bl... more The detection of nuclear radiation necessitates the availability of new generations of tunable blue emitting fluorophores with high emission quantum yields. Here we show that pyridyl-1,2,4-triazole based diphenyl boron complexes can provide highly tuneable emission through facile modification of the C5 position of the 1,2,4-triazolato ring. The series of complexes prepared show a wide range of emission from near-UV to green, enabling fine control over the spectral overlap with detectors used in scintillator technology.
ChemInform, 2008
Manganese Catalyzed Asymmetric cis-Dihydroxylation with H2O2. -(DE BOER, J. W.; BROWNE, W. R.; HA... more Manganese Catalyzed Asymmetric cis-Dihydroxylation with H2O2. -(DE BOER, J. W.; BROWNE, W. R.; HARUTYUNYAN, S. R.; BINI, L.; TIEMERSMA-WEGMAN, T. D.; ALSTERS, P. L.; HAGE, R.; FERINGA*, B. L.; Chem. Commun. (Cambridge) 2008, 32, 3747-3749; Stratingh Inst. Chem., Univ. Groningen, NL-9747 AG Groningen, Neth.; Eng.) -M. Paetzel 52-142