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Thomas J. Meyer

Publications and source records attributed to Thomas J. Meyer.

At least 19 recordsLinked to original sources
PubMed2001

Isolation and Characterization of the Osmium(V)-Imido Complex [Os(V)(Tp)(Cl)(2)(NH)] We are grateful to the National Science Foundation under Grant number CHE-9503738, the Los Alamos National Laboratory (DOE) under Grant Number 10730-001-00-2C, and the Laboratory Directed Research and Development Program for support of this research. M. H. V. Huynh gratefully acknowledges postdoctoral fellowship support from the Directorapos;s Office of Los Alamos National Laboratory. Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy under Contract W-7405-ENG-36. We also thank Dr. Paul R. Sharp (Professor of Chemistry, University of Missouri, Columbia, MO, 65211) for the information on transition metal parent imido complexes.

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PubMed1999

Intervalence Transfer at the Localized-to-Delocalized, Mixed-Valence Transition in Osmium Polypyridyl Complexes.

The mixed-valence complexes [(bpy)(2)(Cl)Os(III)(BL)Os(II)(Cl)(bpy)(2)](3+) and [(tpy)(bpy)Os(III)(BL)Os(II)(bpy)(tpy)](5+) (bpy is bipyridine; tpy is 2,2':6',2' '-terpyridine; BL is a bridging ligand, either 4,4'-bipyridine (4,4'-bpy) or pyrazine (pz)) have been prepared and studied by infrared and near-infrared measurements in different solvents. For BL = 4,4'-bpy, there is clear evidence for localized Os(II) and Os(III) oxidation states in the appearance of the expected two interconfigurational dpi --> dpi bands at Os(III) and additional, broad absorption features in the near-infrared arising from intervalence transfer (IT) transitions. For [(bpy)(2)(Cl)Os(pz)Os(Cl)(bpy)(2)](3+) and [(tpy)(bpy)Os(pz)Os(bpy)(tpy)](5+), unusually intense nu(pz) bands appear in the infrared at 1599 cm(-)(1) (epsilon = 2600 M(-)(1) cm(-)(1)) for the former and at 1594 cm(-)(1) (epsilon = 2020 M(-)(1) cm(-)(1)) for the latter. They provide an oxidation state marker and evidence for localized oxidation states. A series of bands appear in the near-infrared from 2500 to 8500 cm(-)(1) that can be assigned to a combination of interconfigurational dpi --> dpi and IT transitions. In CD(3)CN, in the mid-infrared, bands arising from nu(bpy) ring stretching modes from 1400 to 1500 cm(-)(1) are averaged for [(bpy)(2)(Cl)Os(pz)Os(Cl)(bpy)(2)](3+) or significantly perturbed for [(tpy)(bpy)Os(pz)Os(bpy)(tpy)](5+) compared to electronically isolated Os(II) and Os(III) complexes. The pyrazine-bridged complexes have properties that place them in a new class of mixed-valence molecules, Class II-III having properties associated with both Class II and Class III in the Robin and Day classification scheme. The characteristic features of this class are that oxidation states are localized because of vibrational coupling but that solvent orientational motions are uncoupled because of rapid intramolecular electron transfer.

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PubMed1999

Sensitization of TiO(2) by Phosphonate-Derivatized Proline Assemblies.

Surface electrochemical and photoelectrochemical measurements on ITO (In(2)O(3):Sn) or TiO(2) of two proline assemblies are reported. Surface coverage on ITO of Pbp-pra(Ru(II)b(2)m)-OH(PF(6))(2) and Bpb-pra(Ru(II)b(2)m)-OCH(3)(CF(3)CO(2))(2) are (1.5-2.4) x 10(-)(10) mol/cm(2), comparable to monolayer coverages of (1.5-2.5) x 10(-)(10) mol/cm(2) for [Ru(bpy)(2)(4,4'-(CO(2)H)(2)bpy)](PF(6))(2) and [Ru(bpy)(2)(4,4'-(PO(3)H(2))(2)bpy)](Br)(2). Incident photon-to-current conversion efficiency (IPCE) measured in Gräztel-type photovoltaic cells are sensitive to subtle structural differences in the assemblies. IPCE values for Pbp-pra(Ru(II)b(2)m)-OH(PF(6))(2) and Bpb-pra(Ru(II)b(2)m)-OCH(3)(CF(3)CO(2))(2) are 2% and <0.1%, which are compared to 23% for both [Ru(bpy)(2)(4,4'-(PO(3)H(2))(2)bpy)](Br)(2) and [Ru(bpy)(2)(4,4'-(CO(2)H)(2)bpy)](PF(6))(2) under the same conditions.

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PubMed1999

Formation and Redox Reactivity of Osmium(II) Thionitrosyl Complexes.

Reaction between [Os(VI)(tpm)(Cl)(2)(N)](PF(6)) (tpm = tris(1-pyrazolyl)methane) (1) or Os(VI)(Tp)(Cl)(2)(N) (Tp = hydrotris(1-pyrazolyl)borate anion) (2) and CS(2) + N(3)(-) in acetone gives the corresponding thionitrosyl complexes, (-)SCN, and N(2). There is an extensive reactivity chemistry of the thionitrosyl group in [Os(II)(tpm)(Cl)(2)(NS)](PF(6)) (3b). Reaction between 3b and PPh(3) occurs with S-atom transfer to give [Os(IV)(tpm)(Cl)(2)(NPPh(3))](+) and S=PPh(3). 3b undergoes chemical or electrochemical reduction to give the corresponding Os(II) ammine complex and H(2)S. O-atom transfer from O=NMe(3) to 3b occurs to give Os(III)(tpm)(Cl)(2)(NSO). Competitive NO(+)/NS(+) exchange and S(2)(-) transfer occur in the reaction between [Os(II)(tpm)(Cl)(2)(NS)](BF(4)) (3c) and NO(+) to give a mixture of [Os(VI)(tpm)(Cl)(2)(N)](+) and [Os(II)(tpm)(Cl)(2)(NO)](+).

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PubMed1999

Excited-State Electron Transfer in a Chromophore-Quencher Complex. Spectroscopic Identification of a Redox-Separated State.

In the chromophore-quencher complex fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (Aqphen is 12,17-dihydronaphtho[2,3-h]dipyrido[3,2-a:2',3'-c]-phenazine-12,17-dione; py-PTZ is 10-(4-picolyl)phenothiazine), Aqphen is a dppz derivative, containing a pendant quinone acceptor at the terminus of a rigid ligand framework. This introduces a third, low-lying, ligand-based pi acceptor level localized largely on the quinone fragment. Laser flash excitation of fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (354.7 nm; in 1,2-dichloroethane) results in the appearance of a relatively long-lived transient that decays with tau(298K) = 300 ns (k = 3.3 x 10(6) s(-)(1)). Application of transient absorption, time-resolved resonance Raman, and time-resolved infrared spectroscopies proves that this transient is the redox-separated state fac-[Re(I)(Aqphen(*)(-)())(CO)(3)(py-PTZ(*)(+)())](+) in which the excited electron is localized largely on the quinone portion of the Aqphen ligand.

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PubMed1999

Oxidation of Benzyl Alcohol by a Dioxo Complex of Ruthenium(VI).

The kinetics and mechanism of reduction of trans-[Ru(VI)(tpy)(O)(2)(L)](2+) (L is H(2)O or CH(3)CN; tpy is 2,2':6',2' '-terpyridine) by benzyl alcohol have been studied in water and acetonitrile. The reactions are first order in alcohol and complex in both solvents and give benzaldehyde as the sole oxidation product. In acetonitrile, sequential Ru(VI) --> Ru(IV) and Ru(IV) --> Ru(II)(') steps occur. As shown by FTIR and UV-visible measurements, Ru(II)(') solvolyzes to give [Ru(II)(tpy)(CH(3)CN)(3)](2+) and benzaldehyde. With (18)O-labeled Ru(VI), approximately 50% of the label ends up in the aldehyde product for both the Ru(VI) --> Ru(IV) and Ru(IV) --> Ru(II) steps as shown by FTIR. In water, Ru(VI) --> Ru(IV) reduction is followed by rapid dimerization by &mgr;-oxo formation. Kinetic parameters for the individual redox steps in 0.1 M HClO(4) at 25 degrees C are k(VI)(-->)(IV) = 13.3 +/- 0.8 M(-)(1) s(-)(1) (DeltaH() = 11.4 +/- 0.2 kcal/mol, DeltaS() = -15.0 +/- 1 eu, k(H)/k(D) = 10.4 for alpha,alpha-d(2) benzyl alcohol). In CH(3)CN at 25 degrees C, k(VI)(-->)(IV) = 67 +/- 3 M(-)(1) s(-)(1) (DeltaH() = 7.5 +/- 0.3 kcal/mol, DeltaS() = -33 +/- 2 eu, k(H)/k(D) = 12.1) and k(IV)(-->)(II)(') = 2.4 +/- 0.1 (DeltaH() = 5.1 +/- 0.3 kcal/mol, DeltaS() = -47 +/- 2 eu, k(H)/k(D) = 61.5). On the basis of the (18)O labeling results in CH(3)CN, the O atom of the oxo group transfers to benzyl alcohol in both steps. Mechanisms are proposed involving prior coordination of the alcohol followed by O insertion into a benzylic C-H bond.

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PubMed1999

A New Electron-Transfer Donor for Photoinduced Electron Transfer in Polypyridyl Molecular Assemblies.

A synthetic procedure has been devised for the preparation of the reductive quencher ligand 4-methyl-4'-(N-methyl-p-tolylaminomethyl)-2,2'-bipyridine (dmb-tol), which contains toluidine covalently bound to 2,2'-bipyridine. When bound to Re(I) in [Re(I)(dmb-tol)(CO)(3)Cl], laser flash Re(I) --> dmb metal-to-ligand charge-transfer (MLCT) excitation at 355 nm in CH(3)CN at 298 +/- 2 K is followed by efficient, rapid (<5 ns) appearance of a transient with an absorption feature at 470 nm. The transient spectrum is consistent with formation of the redox-separated state, [Re(I)(dmb(-)-tol(+))(CO)(3)Cl], which returns to the ground state by back electron transfer with k(ET) = (1.05 +/- 0.01) x 10(7) s(-)(1) (tau = 95 +/- 1 ns) at 298 +/- 2 K. Rapid, efficient quenching is also observed in the Ru(II) complex [Ru(4,4'-(C(O)NEt(2))(2)bpy)(2)(dmb-tol)](2+). Based on transient absorption measurements, a rapid equilibrium appears to exist between the initial metal-to-ligand charge-transfer excited state and the redox-separated state, which lies at higher energy. Decay to the ground state is dominated by back electron transfer within the redox-separated state which occurs with k > 4 x 10(8) s(-)(1) at 298 +/- 2 K.

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PubMed1999

Excited-State Electronic Structure in Polypyridyl Complexes Containing Unsymmetrical Ligands.

Step-scan Fourier transform infrared absorption difference time-resolved (S(2)FTIR DeltaA TRS) and time-resolved resonance Raman (TR(3)) spectroscopies have been applied to a series of questions related to excited-state structure in the metal-to-ligand charge transfer (MLCT) excited states of [Ru(bpy)(2)(4,4'-(CO(2)Et)(2)bpy)](2+), [Ru(bpy)(2)(4-CO(2)Et-4'-CH(3)bpy)](2+), [Ru(bpy)(4,4'-(CO(2)Et)(2)bpy)(2)](2+), [Ru(4,4'-(CO(2)Et)(2)bpy)(3)](2+), [Ru(bpy)(2)(4,4'-(CONEt(2))(2)bpy)](2+), [Ru(bpy)(2)(4-CONEt(2)-4'-CH(3)bpy)](2+), and [Ru(4-CONEt(2)-4'-CH(3)bpy)(3)](2+) (bpy is 2,2'-bipyridine). These complexes contain bpy ligands which are either symmetrically or unsymmetrically derivatized with electron-withdrawing ester or amide substituents. Analysis of the vibrational data, largely based on the magnitudes of the nu(CO) shifts of the amide and ester substituents (Deltanu(CO)), reveals that the ester- or amide-derivatized ligands are the ultimate acceptors and that the excited electron is localized on one acceptor ligand on the nanosecond time scale. In the unsymmetrically substituted acceptor ligands, the excited electron is largely polarized toward the ester- or amide-derivatized pyridine rings. In the MLCT excited states of [Ru(bpy)(2)(4,4'-(CO(2)Et)(2)bpy)](2+) and [Ru(bpy)(2)(4,4'-(CONEt(2))(2)bpy)](2+), Deltanu(CO) is only 60-70% of that observed upon complete ligand reduction due to a strong polarization interaction in the excited state between the dpi(5) Ru(III) core and the excited electron.

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PubMed1998

Water Oxidation by [(tpy)(H(2)O)(2)Ru(III)ORu(III)(H(2)O)(2)(tpy)](4+).

The complex [(tpy)(C(2)O(4))Ru(III)ORu(III)(C(2)O(4))(tpy)].8H(2)O (1.8H(2)O) (tpy is 2,2':6',2"-terpyridine) has been prepared and characterized by X-ray crystallography and FTIR, resonance Raman, and (1)H NMR spectroscopies. From the results of the X-ray analysis, angleRuORu is 148.5 degrees with a torsional angle (O(22)-Ru(2)-O(1)-Ru(1)-O(12)) of 22.7 degrees and there is a short Ru-O bridge distance of 1.843 Å. 1 undergoes a chemically reversible one-electron, pH-independent oxidation at 0.73 V vs NHE (0.49 V vs SCE) from pH = 4-8 and a pH-dependent, two-electron, chemically irreversible reduction at -0.35 V below pH = 4.0. Addition of 1.8H(2)O to strong acid generates [(tpy)(H(2)O)(2)Ru(III)ORu(III)(H(2)O)(2)(tpy)](4+) (2), which has been characterized by UV-visible, resonance Raman, and (1)H NMR measurements. In pH-dependent cyclic voltammograms there is evidence for a series of redox couples interrelating oxidation states from Ru(II)ORu(II) to Ru(V)ORu(V). In contrast to the "blue dimer", cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+), oxidation state Ru(IV)ORu(IV) (Ru(V)ORu(III)?) does appear as a stable oxidation state. Oxidation of Ru(IV)ORu(IV) by Ce(IV) in 0.1 M HClO(4) is followed by rapid O(2) production and appearance of an anated form of Ru(IV)ORu(IV). O(2) formation is in competition with oxidative cleavage of Ru(V)ORu(V) by Ce(IV) to give [Ru(VI)(tpy)(O)(2)(OH(2))](2+). Anation and oxidative cleavage prevent this complex from being a true catalyst for water oxidation.

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PubMed1998

Electropolymerized Films of Macromeric Assemblies.

The polymer poly[4-(2-aminoethyl)styrene], prepared by living anionic polymerization, has been derivatized by amide coupling to [Ru(II)(vbpy)(2)(4-CO(2)H-4'-CH(3)bpy)](2+) (vbpy is 4-vinyl-4'-methyl-2,2'-bipyridine; 4-CO(2)H-4'-CH(3)bpy is 4-methyl-2,2'-bipyridine-4'-carboxylic acid). The resulting "macromer" can be electropolymerized on a variety of electrode materials by reductive electropolymerization. Compared to similar films of poly[Ru(II)(vbpy)(3)](PF(6))(2): (1) the macromeric films are considerably rougher, apparently having open, local microporous structures; (2) they undergo comparable rates of intrafilm charge transfer; and (3) they have shortened metal-to-ligand charge transfer (MLCT) excited state lifetimes, apparently due to quenching by film-based trap sites. Stable films of a mixed polymer have also been prepared by sequential addition of [Ru(II)(bpy)(2)(4-CO(2)H-4'-CH(3)bpy)](2+) and then the vbpy derivative.

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PubMed1998

Mid-Infrared Spectrum of [Ru(phen)(3)](2+).

Time-resolved infrared spectra in the fingerprint region (1300-1700 cm(-)(1)) are reported for the metal-to-ligand charge-transfer (MLCT) excited state(s) of [Ru(phen)(3)](2+) and [Os(phen)(DAS)(2)](2+) (phen is 1,10-phenanthroline; DAS is 1,2-bis(diphenylarsino)ethane) in acetonitrile-d(3) at 298 K. The spectra are assigned by comparison to electrochemically generated [Ru(III)(phen)(3)](3+) and [Ru(II)(phen(*)(-)())(phen)(2)](+). The data provide clear evidence for the localized description [Ru(III)(phen(*)(-)())(phen)(2)](2+) on the approximately 100 ns time scale. They also give insight into electronic distribution in the excited state, aid in the interpretation of the time-resolved resonance Raman spectrum of [Ru(phen)(3)](2+), and suggest why measuring ground- and excited-state resonance Raman spectra of phen complexes is difficult.

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PubMed1998

Reactivity of Osmium(VI) Nitrides with the Azide Ion. A New Synthetic Route to Osmium(II) Polypyridyl Complexes.

There is an extensive reactivity chemistry between trans-[Os(VI)(tpy)(Cl)(2)(N)](+) (1) (tpy = 2,2':6',2"-terpyridine) and N(3)(-). Reaction of 1 with N(3)(-) in CH(2)Cl(2) or acetone occurs by electron transfer to give trans,trans-(tpy)(Cl)(2)Os(II)(N(2))Os(II)(Cl)(2)(tpy). In CH(3)CN, trans-Os(II)(tpy)(Cl)(2)(N(2)) forms but undergoes solvolysis to give trans-Os(II)(tpy)(Cl)(2)(CH(3)CN). 1 reacts with excess N(3)(-) in CH(3)CN to give Os(III)(tpy)(Cl)(2)(5-CH(3)-tetrazolate), which has been characterized by X-ray crystallography. This is the first known Os-tetrazolato complex. 1 reacts with N(3)(-) in the presence of CS(2) to give trans-[Os(II)(tpy)(Cl)(2)(NS)](+), SCN(-), and N(2).

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PubMed1998

Preparation and Photophysical Properties of Amide-Linked, Polypyridylruthenium-Derivatized Polystyrene.

The polymer poly(4{2-[N,N-bis(trimethylsilyl)amino]ethyl}styrene), prepared by anionic polymerization and of low polydispersity (M(w)/M(n) = 1.10-1.18), has been derivatized by amide linkage to [Ru(II)(bpy)(2)(4-(CO-)-4'-CH(3)-bpy)-](2+) (bpy is 2,2'-bipyridine; 4-(CO-)-4'-CH(3)-bpy is 4-carbonyl-4'-methyl-2,2'-bipyridine). Unreacted amine sites were converted into acetamides by treatment with acetic anhydride to give derivatized polymers of general formula [PS-CH(2)CH(2)NHCO(Ru(II)(n)()Me(m)())](PF(6))(2)(n)(), where m + n = 11, 18, or 25, PS represents the polystyrene backbone, and Ru(II) and Me represent the attached complex and acetamide, respectively. Spectral and electrochemical properties of the derivatized polymers are similar to those of the model [Ru(bpy)(2)(4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy)](2+) (4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy is 4'-methyl-2,2'-bipyridinyl-4-(2-phenylethylamide)), but emission quantum yields (phi(em)) and time-resolved emission decays are slightly dependent on the level of Ru(II) loading, with nonexponential, irradiation-dependent decays appearing at high loadings. The decays could be fitted satisfactorily to the first derivative of the Williams-Watts distribution function. These results are discussed with reference to possible structural and multichromophoric effects on excited-state decay.

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