Radical Monoanion Research Articles

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

The crystal structures of [M2(phen)4(H2O)2(C4O4)]· C4O4· 8H2O [M = Co2+ (1), Mn2+ (2); phen: 1,10-phenanthroline] complexes have been prepared and characterized by IR spectroscopy, thermal analysis and single X-ray diffraction techniques. Their structures consist of [Co2(phen)4(H2O)2(C4O4)]2+ (1) and [Mn2(phen)4(H2O)2(C4O4)]2+ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C4O 4 2− (SQ2−) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the μ-1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M–M separation being 8.053(7) A (1) and 8.175(4) A (2), respectively, while the other squarate acts as a counter anion. The voltammetric behaviour of complexes (1) and (2) was investigated in DMSO (dimethylsulfoxide) solution by cyclic voltammetry using n-Bu4NClO4 as supporting electrolyte. The complexes exhibit both metal and ligand centred electroactivity in the potential ±1.75 V versus Ag/AgCl reference electrode. The dianion SQ2− is oxidized in two consecutive steps to the corresponding radical monoanion and neutral form.

Infra-red and Raman spectroscopic study of tetra-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with tert-butyl derivatives

The infra-red spectroscopic data for a series of 13 homoleptic substituted bis(phthalocyaninato) rare earth complexes with tervalent rare earths M III(TBPc) 2 [M = Y, Pr, …, Lu except La, Ce and Pm; TBPc = dianion of 3(4),12(13),21(22),30(31)-tetra( tert-butyl)-phthalocyanine] have been collected with resolution of 2 cm −1. Raman spectroscopic properties in the range of 500–1800 cm −1 for these double-deckers M III(TBPc) 2 have been collected using laser excitation sources emitting at 632.8 nm. Both the IR and Raman spectra for M III(TBPc) 2 are more complicated than those of homoleptic bis(phthalocyaninato) rare earth analogues due to the decreased molecular symmetry of these double-decker compounds. For this series, the IR typical marker band of (TBPc) − appears as an intense absorption at 1314–1319 cm −1, attributed to the pyrrole stretching. Under excitation at 632.8 nm that is in close resonance with the main Q absorption band of phthalocyanine ligand, typical Raman marker band of the monoanion radical (TBPc) − was observed at 1515–1530 cm −1 resulting from aza C N stretching. Both techniques reveal that the frequencies of pyrrole stretching, isoindole breathing and aza stretchings depend on the rare earth ionic size, shifting to higher energy along with the lanthanide contraction due to the increased ring–ring interaction across the series.

Preparation, spectroscopic characterization, and deprotonation reactions of Si(NHR)4 (R = i-Pr, t-Bu, p-tolyl) — EPR identification of persistent radicals formed by oxidation of polyimidosilicates

Treatment of Cl2Si(NH-t-Bu)2 (6a) with t-BuNH2 in boiling toluene yields trisamino(chloro)silane ClSi(NH-t-Bu)3 (7); formation of the tetraaminosilane Si(NH-t-Bu)4 is not observed. The reaction of SiCl4 with 4 equiv. of LiNHR produces the corresponding tetraaminosilanes Si(NHR)4 (2a, R = i-Pr; 2b, R = t-Bu; 2c, R = p-tol) in good yields. When the sterically demanding adamantyl derivative LiHNAd is employed, only disubstitution occurs to form Cl2Si(NHAd)2 (6b). Oxidation of the dimeric imidosilicates {Li3[Si(NR)3(NHR)]·THF}2 (3a, R = i-Pr; 3b, R = t-Bu) with 1 mol of iodine produces the persistent radicals {Li2[Si(NR)3(NHR)]·LiI·3THF}·, which, on the basis of EPR spectra, exist as SiN3Li3I cubes in solution. The spirocyclic tetraimidosilicate monoanion radical {[(THF)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(THF)2]}–· (10) is formed upon oxidation of the tetralithiated species {Li4[Si(Nnaph)4]·4Et2O} (1) and {[Li(12-crown-4)]2[(Et2O)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(Et2O)2]} (8) with iodine. The spectroscopic characterization of hexa(amino)disiloxane (t-BuNH)3SiOSi(NH-t-Bu)3 (14) formed from the reaction of Cl3SiOSiCl3 with 6 equiv. of LiNH-t-Bu is discussed. Key words: imido ligands, silicate, radicals, EPR spectra, lithium.

Infrared spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The infrared (IR) spectroscopic data for a series of 15 rare earth double-deckers M[Pc(MeOPhO) 8] 2 [M = Y, La, …, Lu, except Pm; H 2Pc = 2, 3, 9, 10, 16, 17, 23, 24-octakis(4-methoxyphenoxy)phthalocyanine] with tervalent rare earths M III[Pc(MeOPhO) 8] 2 (M = Y, La, …, Lu except Ce and Pm) and intermediate-valent cerium Ce[Pc(MeOPhO) 8] 2 have been collected with resolution of 2 cm −1. For M III[Pc(MeOPhO) 8] 2, typical IR marker band of the monoradical anion Pc(MeOPhO) 8 − shows characteristic absorption band whose frequency linearly varies in the range from 1313 cm −1 as a weak band for La[Pc(MeOPhO) 8] 2 to 1324 cm −1 as a medium band for Lu[Pc(MeOPhO) 8] 2 along with the decrease of rare earth ionic size. For Ce[Pc(MeOPhO) 8] 2, a weak band at 1324 cm −1 with contribution from pyrrole stretching was the marker IR band of phthalocyanine dianion Pc 2−. In conclusion, all the metal size-dependent IR absorptions should be contributed primarily from the vibrations of pyrrole, isoindole stretching, breathing or deformation or aza stretching of the Pc ring.

Electrochemistry of fullerene C 60 embedded in Langmuir–Blodgett films of artificial lipids on electrodes

A stable Langmuir monolayer of fullerene C 60 and an artificial lipid was formed at the air–water interface and the monolayer was transferred onto an electrode as a Langmuir–Blodgett (LB) film. Here, we focus on the importance of cationic matrix lipid films to the facile electrochemistry of C 60 embedded in a LB film of cationic lipids on an electrode in aqueous media. The electrochemically generated radical monoanion of C 60 embedded in a film of cationic lipid, tridodecylmethylammonium bromide ( 1), was stable during continuous potential cycling, while the C 60 radical monoanion became unstable after the generation of C 60 2− due to the exfoliation of the LB film from the electrode. On the basis of the electrolyte dependence and the charge dependence of the matrix lipids, a possible electron-transfer mechanism for the C 60/artificial lipid LB film-modified electrodes is presented.

Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes: Part 13. The Raman characteristics of phthalocyanine in unsubstituted and peripherally octa(octyloxy)-substituted homoleptic bis(phthalocyaninato) rare earth complexes

The Raman spectroscopic data in the range of 500–1800 cm −1 for two series of thirty homoleptic bis(phthalocyaninato) rare earth complexes M(Pc) 2 and M[Pc(OC 8H 17) 8] 2 [M = Y, La–Lu except Pm; H 2Pc = unsubstituted phthalocyanine, H 2Pc(OC 8H 17) 8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine] have been collected and comparatively studied using laser excitation sources emitting at 633 and 785 nm. Under both laser excitations, the marker Raman band of Pc 2− and [Pc(OC 8H 17) 8] 2− in the Raman spectra of Ce(Pc) 2 and Ce[Pc(OC 8H 17) 8] 2 appears as a strong scattering at 1498–1501 cm −1 with contributions from both pyrrole C C and aza C N stretches together with isoindole stretchings. This band has been found to upshift to 1502–1528 cm −1 in the Raman spectra of M III(Pc) 2 and M III[Pc(OC 8H 17) 8] 2 as the marker Raman band of phthalocyanine monoanion radicals, Pc − or [Pc(OC 8H 17) 8] − . With laser excitation at 633 nm, Raman vibrations derived from isoindole ring and aza stretchings in the range of 1300–1600 cm −1 for both series are selectively intensified. In contrast, when excited with laser radiation of 785 nm, the ring radial vibrations of isoindole moieties and dihedral plane deformations between 500 and 1000 cm −1 for M(Pc) 2 and M[Pc(OC 8H 17) 8] 2 intensify to become the strongest scatterings. The present Raman results also reveal that the frequencies of Pc breathing, pyrrole stretching, isoindole stretchings, aza stretchings and coupling of pyrrole and aza stretchings depend on the rare earth ionic size, shifting to higher wavenumbers along with the lanthanide contraction due to the increased ring–ring interaction across the series. Moreover, under these laser excitations, in particular under 785 nm laser line, the Raman spectrum appearance, i.e., the pattern of relative intensities, also changes systematically depending on the rare earth ionic size.

Electrochemical investigation of superoxide anion scavenging ability of 1,2,3-triketohydrindene hydrate in aprotic solvents

1,2,3-Triketohydrindene hydrate (NHy) shows well-defined redox electrochemistry in the formation of monoanionic radical (NHy −) and dianion (NHy 2−) in nitrogen saturated aprotic solvents such as acetonitrile and dimethylsulfoxide. Cyclic voltammetry reveals that in an oxygen-saturated solution of DMSO, the oxidation peak of superoxide anion (O 2 −) at −0.7 V versus Ag/AgCl wire electrode, decreases systematically with increasing NHy concentration. The similar behaviour is observed in the rotating disk voltammetry. On Pt disk, oxygen is reduced to O 2 − at a constant potential of −0.8 V and at Pt ring, O 2 − is oxidised to oxygen and the corresponding limiting current plateau in the ring voltammogram is decreased linearly as [NHy] is increased. In aqueous solutions, NHy is found to exhibit completely different redox chemistry due to its structural changes and hence showed no favourable redox potentials for efficient quenching of O 2 −.

Molecular and Electronic Structure of Five-Coordinate Complexes of Iron(II/III) Containing o-Diiminobenzosemiquinonate(1−) π Radical Ligands

The reaction of the ligand N-phenyl-1,2-benzenediamine (N-phenyl-o-phenylenediamine), H2[L(PDI)], in dry acetonitrile with [FeIII(dmf)6](ClO4)3 (dmf = N,N-dimethylformamide) affords the dimer (mu-NH,NH)[FeIII(L(ISQ))(L(PDI))]2 (1), where (L(ISQ))*- represents the pi radical monoanion N-phenyl-o-diiminobenzosemiquinonate and (L(PDI))2- is its one-electron-reduced, closed-shell form. Complex 1 possesses a diamagnetic ground-state St = 0. Addition reactions of tri-n-butylphosphane, tert-butyl isocyanide, cyclohexyl isocyanide, 4,5-diphenylimidazole, and 4-(1-phenylpentyl)pyridine with 1 in acetonitrile or toluene yields [FeII(L(ISQ))2(PBu3)] (2), [Fe(II)(L(ISQ))2(CN-tBu)] (4), [FeII(L(ISQ))2(CNCy)] (5), [FeIII(L(ISQ))2(Ph2Im)] (6), and [FeIII(L(ISQ))(L(PDI))(BuPhCH-py)].BuPhCH-py (7). Oxidation of 1 with iodine affords [FeIII(L(ISQ))2I] (3), and oxidation of 2 with ferrocenium hexafluorophosphate yields [FeIII(L(ISQ))2(PBu3)](PF6) (2ox). The structures of complexes 2, 2ox, 3, 5, 6, and 7 have been determined by X-ray crystallography at 100(2) K. Magnetic susceptibility measurements and EPR, UV-vis, and Mössbauer spectroscopy have established that mononuclear complexes containing the [FeII(L(ISQ))2X] chromophore (2, 4, 5) are diamagnetic (St = 0) whereas those with an [FeIII(L(ISQ))2X]n chromophore (3, 2(ox), 6) are paramagnetic (St = 1/2) and those with an [FeIII(L(ISQ))(L(PDI))X] chromophore (7) possess an St = 1 ground state. It is established that all ferric species have an intrinsic intermediate spin (SFe = 3/2) which is intramolecularly antiferromagnetically coupled to one or two (L(ISQ))*- ligand radicals yielding an St = 1 (7) or St = 1/2 (2ox, 3, 6) ground state, respectively. In the ferrous complexes 2, 4, and 5 the intrinsic spin at the iron ion is either low spin (SFe = 0) or intermediate spin (SFe = 1). Antiferromagnetic coupling between two radicals (L(ISQ))*- or, alternatively, between the intermediate spin ferrous ion and two radicals yields then the observed diamagnetic ground state. In 1 two [FeIII(L(ISQ))(L(PDI))] halves with S = 1 couple antiferromagnetically affording an St = 0 ground state.

Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes: Part 14. The infrared and Raman characteristics of phthalocyanine in “pinwheel-like” homoleptic bis[1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato] rare earth(III) double-decker complexes

The infrared (IR) spectroscopic data and Raman spectroscopic properties for a series of 13 “pinwheel-like” homoleptic bis(phthalocyaninato) rare earth complexes M[Pc(α-OC 5H 11) 4] 2 [M = Y and Pr–Lu except Pm; H 2Pc(α-OC 5H 11) 4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyanine] have been collected and comparatively studied. Both the IR and Raman spectra for M[Pc(α-OC 5H 11) 4] 2 are more complicated than those of homoleptic bis(phthalocyaninato) rare earth analogues, namely M(Pc) 2 and M[Pc(OC 8H 17) 8] 2, but resemble (for IR) or are a bit more complicated (for Raman) than those of heteroleptic counterparts M(Pc)[Pc(α-OC 5H 11) 4], revealing the decreased molecular symmetry of these double-decker compounds, namely S 8. Except for the obvious splitting of the isoindole breathing band at 1110–1123 cm −1, the IR spectra of M[Pc(α-OC 5H 11) 4] 2 are quite similar to those of corresponding M(Pc)[Pc(α-OC 5H 11) 4] and therefore are similarly assigned. With laser excitation at 633 nm, Raman bands derived from isoindole ring and aza stretchings in the range of 1300–1600 cm −1 are selectively intensified. The IR spectra reveal that the frequencies of pyrrole stretching and pyrrole stretching coupled with the symmetrical C H bending of –CH 3 groups are sensitive to the rare earth ionic size, while the Raman technique shows that the bands due to the isoindole stretchings and the coupled pyrrole and aza stretchings are similarly affected. Nevertheless, the phthalocyanine monoanion radical Pc′ − IR marker band of bis(phthalocyaninato) complexes involving the same rare earth ion is found to shift to lower energy in the order M(Pc) 2 > M(Pc)[Pc(α-OC 5H 11) 4] > M[Pc(α-OC 5H 11) 4] 2, revealing the weakened π–π interaction between the two phthalocyanine rings in the same order.

UV/Vis/NIR spectral properties of triarylamines and their corresponding radical cations

The one-electron oxidation potential of 10 triarylamines 1– 10 with all permutations of chloro-, methoxy- and methyl-substituents in the three para-positions were determined by cyclic voltammetry. The half wave potential E 1/2(I) of the first oxidation wave correlates linearly with the number of chloro- and methoxy-substituents. A high long-term stability of the first oxidation wave for all triarylamines was observed by multi-cycle thin-layer measurements. AM1-CISD derived values of the absorption energies are in good agreement with the experiments but differ strongly for the oscillator strengths as well as for neutral compounds 1– 10 and their corresponding mono radical cations. The small solvent dependence of the experimental UV/Vis spectra in CH 2Cl 2 and MeCN reflects a minor charge transfer (CT) character of the electronic transitions of neutral and cationic compounds.

Structural study of thin films of neutral and potassium-doped oligophenylenes on Cu(1 0 0)

Well-ordered thin films of p-oligophenylenes, p-quaterphenyl (4P), p-quinquephenyl (5P) and p-sexiphenyl (6P), were prepared on a Cu(1 0 0) single crystal substrate by vacuum vapor deposition. Their structures were investigated by infrared reflection absorption spectroscopy (IRRAS) and low energy electron diffraction (LEED). In the monolayers, p-oligophenylenes are physisorbed with their axes parallel to the substrate and form a regular two-dimensional arrangement. This structure is unaltered even in multilayers up to a thickness of a few nanometers. In the potassium (K)-doped 4P films, on the other hand, the arrangement is disrupted due to the perturbation by the dopant. The IRRAS investigation including observed and calculated spectra suggests that the radical monoanions are formed upon low-level doping, followed by saturation of the radical monoanion concentration and appearance of the dianions on increasing the amount of K.

Redox-Noninnocence of the S,S‘-Coordinated Ligands in Bis(benzene-1,2-dithiolato)iron Complexes

The electronic structures of complexes of iron containing two S,S'-coordinated benzene-1,2-dithiolate, (L)(2)(-), or 3,5-di-tert-butyl-1,2-benzenedithiolate, (L(Bu))(2)(-), ligands have been elucidated in depth by electronic absorption, infrared, X-band EPR, and Mossbauer spectroscopies. It is conclusively shown that, in contrast to earlier reports, high-valent iron(IV) (d(4), S = 1) is not accessible in this chemistry. Instead, the S,S'-coordinated radical monoanions (L(*))(1)(-) and/or (L(Bu)(*))(1)(-) prevail. Thus, five-coordinate [Fe(L)(2)(PMe(3))] has an electronic structure which is best described as [Fe(III)(L)(L(*))(PMe(3))] where the observed triplet ground state of the molecule is attained via intramolecular, strong antiferromagnetic spin coupling between an intermediate spin ferric ion (S(Fe) = (3)/(2)) and a ligand radical (L(*))(1)(-) (S(rad) = (1)/(2)). The following complexes containing only benzene-1,2-dithiolate(2-) ligands have been synthesized, and their electronic structures have been studied in detail: [NH(C(2)H(5))(3)](2)[Fe(II)(L)(2)] (1), [N(n-Bu)(4)](2)[Fe(III)(2)(L)(4)] (2), [N(n-Bu)(4)](2)[Fe(III)(2)(L(Bu))(4)] (3); [P(CH(3))Ph(3)][Fe(III)(L)(2)(t-Bu-py)] (4) where t-Bu-py is 4-tert-butylpyridine. Complexes containing an Fe(III)(L(*))(L)- or Fe(III)(L(Bu))(L(Bu)(*))- moiety are [N(n-Bu)(4)][Fe(III)(2)(L(Bu))(3)(L(Bu)(*))] (3(ox)()), [Fe(III)(L)(L(*))(t-Bu-py)] (4(ox)()), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))] (7), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))(2)] (8), and [Fe(III)(L(Bu))(L(Bu)(*))(PPr(3))] (9), where Pr represents the n-propyl substituent. Complexes 2, 3(ox)(), 4, [Fe(III)(L)(L(*))(PMe(3))(2)] (6), and 9 have been structurally characterized by X-ray crystallography.

Infrared spectroscopic characteristics of phthalocyanine in mixed [tetrakis(4-chlorophenyl)porphyrinato](phthalocyaninato) rare earth double-deckers

The infra-red (IR) spectroscopic data for a series of 15 mixed [tetrakis(4-chlorophenyl)porphyrinato](phthalocyaninato) rare earth double-decker complexes with tervalent rare earths M III(TClPP)(Pc) (M = Y, La, …, Lu except Ce and Pm) and intermediate-valent cerium Ce(TClPP)(Pc) have been collected with resolution of 2 cm −1. For M III(TClPP)(Pc), typical IR marker band of the monoradical anion Pc − shows the most intense absorption band whose frequency linearly varies in the range from 1311 cm −1 for La(TClPP)(Pc) to 1320 cm −1 for Lu(TClPP)(Pc) along with the decrease of rare earth ionic size. The peaks at 1016–1023 cm −1 are assigned to C Cl stretchings. For Ce(TClPP)(Pc), a medium band at 1329 cm −1 with contribution from pyrrole stretching was the marker IR band of phthalocyanine dianion Pc 2−. The TClPP − IR marker band at ca. 1270–1300 cm −1 was not observed for these compounds. These facts indicate that the hole in these double-deckers is mainly localized at the phthalocyanine ring.

High Covalence in CuSO4 and the Radicalization of Sulfate: An X‐Ray Absorption and Density Functional Study.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High Covalence in CuSO4 and the Radicalization of Sulfate: An X-ray Absorption and Density Functional Study

Sulfur K-edge X-ray absorption spectroscopy (XAS) of anhydrous CuSO(4) reveals a well-resolved preedge transition feature at 2478.8 eV that has no counterpart in the XAS spectra of anhydrous ZnSO(4) or copper sulfate pentahydrate. Similar but weaker preedge features occur in the sulfur K-edge XAS spectra of [Cu(itao)SO(4)] (2478.4 eV) and [Cu[(CH(3))(6)tren]SO(4)] (2477.7 eV). Preedge features in the XAS spectra of transition metal ligands are generally attributed to covalent delocalization of a metal d-orbital hole into a ligand-based orbital. Copper L-edge XAS of CuSO(4) revealed that 56% of the Cu(II) 3d hole is delocalized onto the sulfate ligand. Hybrid density functional calculations on the two most realistic models of the covalent delocalization pathways in CuSO(4) indicate about 50% electron delocalization onto the sulfate oxygen-based 2p orbitals; however, at most 14% of that can be found on sulfate sulfur. Both experimental and computational results indicated that the high covalence of anhydrous CuSO(4) has made sulfate more like the radical monoanion, inducing an extensive mixing and redistribution of sulfur 3p-based unoccupied orbitals to lower energy in comparison to sulfate in ZnSO(4). It is this redistribution, rather than a direct covalent interaction between Cu(II) and sulfur, that is the origin of the observed sulfur XAS preedge feature. From pseudo-Voigt fits to the CuSO(4) sulfur K-edge XAS spectrum, a ground-state 3p character of 6% was quantified for the orbital contributing to the preedge transition, in reasonable agreement with the DFT calculation. Similar XAS fits indicated 2% sulfur 3p character for the preedge transition orbitals in [Cu(itao)SO(4)] and [Cu[(CH(3))(6)tren]SO(4)]. The covalent radicalization of ligands similar to sulfate, with consequent energy redistribution of the virtual orbitals, represents a new mechanism for the induction of ligand preedge XAS features. The high covalence of the Cu sites in CuSO(4) was found to be similar to that of Cu sites in oxidized cupredoxins, including its anistropic nature, and can serve as the simplest inorganic examples of intramolecular electron-transfer processes.

Vibrational spectroscopic characteristics of phthalocyanine and naphthalocyanine in sandwich‐type phthalocyaninato and porphyrinato rare earth complexes. Part 11—Raman spectroscopic characteristics of phthalocyanine in mixed [tetrakis(4‐chlorophenyl)porphyrinato](phthalocyaninato) rare earth double‐deckers

AbstractRaman spectroscopic data in the range 500–1800 cm−1 for a series of 15 mixed [tetrakis(4‐chlorophenyl)porphyrinato](phthalocyaninato) double‐decker complexes with tervalent rare earths MIII(TClPP)(Pc) (M = Y, LaLu except Ce and Pm) and intermediate‐valent cerium Ce(TClPP)(Pc) were collected using laser excitation sources emitting at 632.8 and 785 nm. Comparison with the Raman spectra of corresponding bis(phthalocyaninato) rare earths reveals that the Raman characteristics of mixed‐ring double‐deckers are dominated by the phthalocyaninato‐metal fragment M(Pc) and phthalocyanine exists as the monoradical anion Pc•− in MIII(TClPP)(Pc) and the dianion Pc2− in Ce(TClPP)(Pc), respectively. With excitation at 632.8 nm, which is in close resonance with the main Q absorption band of the phthalocyanine ligand, a typical Raman marker band of the monoanion radical Pc•− was observed at 1512–1519 cm−1 as a weak band resulting from the coupling of pyrrole CC and aza CN stretchings. For Ce(TClPP)(Pc), a strong band at 1492 cm−1 with contributions from both pyrrole CC and aza CN stretchings and also isoindole stretching was the marker Raman band of Pc2−. When excited with laser radiation of 785 nm, which is far away from the main Q absorption band of the phthalocyanine ligand, the marker Raman band of Pc•− in MIII(TClPP)(Pc) is observed at 1495–1514 cm−1 and of Pc2− in Ce(TClPP)(Pc) at 1511 cm−1 as a strong band. Copyright © 2004 John Wiley & Sons, Ltd.

Electrochemical and Chemical Reduction of Fullerenes C60 and C70 Embedded in Cast Films of Artificial Lipids in Aqueous Media

In this paper, we first describe the electrochemical behavior of C60 and of C70 embedded in films of lipids and cationic amphiphiles on basal-plane pyrolytic graphite (BPG) electrodes in aqueous media. The electrode modifiers used were mainly tridodecylmethylammonium bromide (3C12N+Br-), tetraalkylammonium bromide (4CnN+Br-, n = 5, 6, 7, 8, 10, 12, and 16), and dihexadecyldimethylammonium poly(styrene sulfonate) (2C16N+PSS-). The generated radical monoanions and dianions of C60 and C70 on the electrodes were stable during continuous potential cycling, but the C70 radical monoanion became unstable after the generation of C70•3-, which is not consistent with the behavior of C60. On the basis of the electrolyte dependence, a possible electron-transfer mechanism of fullerenes/lipid (amphiphile)-coated electrodes was presented. Second, a spectroelectrochemical study was conducted for C60/3C12N+Br--modified electrodes, and the results of simultaneous measurements of current and absorbance changes during potenti...

Lithiation of (tBuNH)3PNSiMe3 and formation of tetraimidophosphate complexes containing M3O3 rings (M = Li, K): X-ray structure of the stable radical [(Me3SiN)P(mu3-N(t)Bu)3[mu3-Li(THF)]3(OtBu)).

The reaction of ((t)BuNH)(3)PNSiMe(3) (1) with 1 equiv of (n)BuLi results in the formation of Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] (2); treatment of 2 with a second equivalent of (n)BuLi produces the dilithium salt Li(2)[P(NH(t)Bu)(N(t)Bu)(2)(NSiMe(3))] (3). Similarly, the reaction of 1 and (n)BuLi in a 1:3 stoichiometry produces the trilithiated species Li(3)[P(N(t)Bu)(3)(NSiMe(3))] (4). These three complexes represent imido analogues of dihydrogen phosphate [H(2)PO(4)](-), hydrogen phosphate [HPO(4)](2)(-), and orthophosphate [PO(4)](3)(-), respectively. Reaction of 4 with alkali metal alkoxides MOR (M = Li, R = SiMe(3); M = K, R = (t)Bu) generates the imido-alkoxy complexes [Li(3)[P(N(t)Bu)(3)(NSiMe(3))](MOR)(3)] (8, M = Li; 9, M = K). These compounds were characterized by multinuclear ((1)H, (7)Li, (13)C, and (31)P) NMR spectroscopy and, in the cases of 2, 8, and 9.3THF, by X-ray crystallography. In the solid state, 2 exists as a dimer with Li-N contacts serving to link the two Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] units. The monomeric compounds 8 and 9.3THF consist of a rare M(3)O(3) ring coordinated to the (LiN)(3) unit of 4. The unexpected formation of the stable radical [(Me(3)SiN)P(mu(3)-N(t)Bu)(3)[mu(3)-Li(THF)](3)(O(t)Bu)] (10) is also reported. X-ray crystallography indicated that 10 has a distorted cubic structure consisting of the radical dianion [P(N(t)Bu)(3)(NSiMe(3))](.2)(-), two lithium cations, and a molecule of LiO(t)Bu in the solid state. In dilute THF solution, the cube is disrupted to give the radical monoanion [(Me(3)SiN)((t)BuN)P(mu-N(t)Bu)(2)Li(THF)(2)](.-), which was identified by EPR spectroscopy.

Intramolecular electron transfer mediated by a tetrathiafulvalene (TTF) bridge

Unprecedented fused acceptor-donor-acceptor triad (Q-TTF-Q) incorporating the donor tetrathiafulvalene (TTF) and the acceptor p-benzoquinone (Q) has been synthesized. The solution UV-Vis spectrum displays a low energy absorption band which is attributed to an intramolecular charge transfer between both antagonistic units. The presence of reversible oxidation and reduction waves for the donor and acceptor moieties was in agreement with the ratio TTF/quinones units. The monoradical anion Q-TTF-Q - . was generated upon chemical reduction and monitored by ESR spectroscopy. This was demonstrated as a Class II mixed valence system with the existence of a temperature dependent intramolecular electron transfer.

Spin trapping of nitric oxide by aci anions of nitroalkanes

In alkaline solutions, nitroalkanes (RCH 2NO 2) undergo deprotonation and rearrange to an aci anion (RHCNO 2 −), which may function as a spin trap. Using electron paramagnetic resonance (EPR) spectroscopy, we have investigated suitability of aci anions of a series of nitroalkanes (CH 3NO 2, CH 3CH 2NO 2, CH 3(CH 2) 2NO 2, and CH 3(CH 2) 3NO 2) to spin trap nitric oxide ( NO). Based on the observed EPR spectra, the general structure of the adducts, formed by addition of NO to RHCNO 2 −, was identified as nitronitroso dianion radicals of general formula [RC(NO)NO 2] 2− in strong base (0.5 M NaOH), and as a mono-anion radical [RCH(NO)NO 2] − in alkaline buffers, pH 10–13. The hyperfine splitting on 14N in the NO 2 moiety (11.2–12.48 G) is distinctly different from the splitting on 14N in the NO moiety of the adducts (5.23–6.5 G). The structure of the adducts was verified using 15N-labeled NO, which produced radicals, in which triplet due to splitting on 14N ( I=1) in 14NO/ aci nitro adducts was replaced by a doublet due to 15N ( I=1/2) in 15NO/ aci nitro adducts. EPR spectra of aci nitromethane/NO adduct recorded in NaOH and NaOD (0.5 M) showed that the hydrogen at α-carbon can be exchanged for deuterium, consistent with structures of the adducts being [CH(NO)NO 2] 2− and [CD(NO)NO 2] 2− , respectively. These results indicate that nitroalkanes could potentially be used as prototypes for development of NO-specific spin traps suitable for EPR analysis.