Tetra-n-butylammonium Perchlorate Research Articles

Synthesis, photophysical, cyclic voltammetry properties, and molecular structure study of novel (5,10,15,20-tetratolylphenyl porphyrinato)zinc(II) with pyrazine

The precursor (5,10,15,20)-tetratolylporphyrin (H2TTP) (1) and Zn(II) complex (5,10,15,20)-tetratolylporphyrinato)zinc(II) [Zn(TTP)] (2) have been synthesized and utilized to afford a novel complex (3) bearing pyrazine as fifth coordination site on axial position, i.e. (pyrazine)(5,10,15,20-tetratolylporphyrinato)zinc(II) hemi-pyrazine hemidichloromethane solvate [Zn(TTP) (pyz)]0.0.5(pyz.CH2Cl2). Photophysical, electrochemical and X-ray diffraction were investigated. The single-crystal X-ray analysis indicated that in complex (3) (i) Zn(II) ion is penta coordinated, (ii) slight displacement of Zn atom by −0.28 Å towards the axial ligand (pyrazine) and (iii) the crystal lattice is made up of two dimensional layers stabilised by C−H…Cg intra- and intermolecular interactions (Cg is the centroid of pyrrole ring). Optical absorption studies revealed a redshifted of the Soret (B) and Q bands of the Zn-porphyrins complexes. Contrarily, a hypsochromic shift of Q bands in emission spectra of the complexes is noted as compared to the H2TPP. Lifetime of the electrons in (1–3) were determined and compared. Overall, this study would assist in understanding the impact of incorporation of pyrazine at the axial position on optical and electronic properties. Cyclic voltammetry (CV) was applied for the study of the electrochemical behavior of both (2) and (3) complexes in 0.2 M Tetra-n-butyl ammonium perchlorate (TBAP) solution in CH2Cl2. The results of electrochemical confirmed the potentials redox peaks shift more negative ca 60 mV to that is caused by the coordination of pyrazine ligand.

Highly Enhanced Electrochemiluminescence Luminophore Generated by Zeolitic Imidazole Framework-8-Linked Porphyrin and Its Application for Thrombin Detection.

Novel and distinct enhancement in electrochemiluminescence (ECL) signals of advanced organic luminophores are of importance for expanding their applications in early diagnosis. This work reported the construction of an ultrasensitive label-free ECL aptasensor for thrombin (TB) detection by grafting zinc proto-porphyrin IX (ZnP) onto an aminated zeolitic imidazole framework-8 (defined as ZnP-NH-ZIF-8 for clarity) as the luminophore. The structure and optical properties of the resulting ZnP-NH-ZIF-8 were carefully characterized. For that, there appeared to be weak ECL radiation for ZnP in dichloromethane (DCM) containing tetra-n-butylammonium perchlorate (TBAP) because of the as-formed singlet-state oxygen via the "reduction-oxidation" route. More notably, the ECL signals display 153-times enhancement for ZnP-NH-ZIF-8, thanks to the excellent catalytic kinetics for the oxygen reduction reaction (ORR). By virtue of the specific interactions of the TB aptamer (TBA) with the TB protein and the highly efficient catalysis of the ZnP-NH-ZIF-8 for ORR, the as-prepared aptasensor showed a wider linear range (0.1 fM∼1 pM) and a lower detection limit (ca. 58.6 aM). This work provides some useful guidelines for synthesis of an advanced organic luminophore with largely boosted ECL signals in ultrasensitive analysis and clinical diagnosis.

A Comprehensive Scope of Peripheral and Axial Substituent Effect on the Spectroelectrochemistry of Boron Subphthalocyanines.

An extensive study of the electrochemical and spectroelectrochemical properties of 14 boron subphthalocyanine (BsubPc) derivatives with various axial and peripheral substituents was performed in 1,2-dichloromethane (CH2Cl2) containing 0.1 M tetra- n-butyl-ammonium perchlorate (TBAP) as the supporting electrolyte. From the cyclic voltammetry results, all compounds exhibit one oxidation and at least two reduction processes within the solvent potential window of +1.6 to -1.8 V vs SCE. It was found that the reversibility of the redox reactions depends on the axial and peripheral substituents and the dipole moment of the boron-to-axial substituent. In general, UV-vis absorption spectra of the singly reduced BsubPc derivatives exhibit three equal intensity peaks in the 450 to 650 nm region that are derived from the maximum BsubPc absorbance peak upon reduction. Axial substituents affect the intensity of the three peaks upon reduction, while peripheral substituents shift the position of the peaks to higher wavelengths. Upon oxidation, the UV-vis absorption profile flattens considerably with only a single broad (∼300 nm) band apparent. Understanding the effect of substituents on the stability of the redox processes of BsubPcs will aid in further development of these materials for applications in organic electronic devices.

Stripping Voltammetry on a new Modified Glassy Carbon Electrode for Lead Content Determination in Soft Water

This study develops a new electrochemical method for quantification of Pb in soft water using stripping voltammetry with a glassy carbon electrode modified with the functionalized azulene: (2E)-2-(azulen-1-ylmethylidene) hydrazine carbothioamide (L) as a complexing polymer film. The optimized steps of the proposed method consisted in experimental establishing of four parameters, namely: reduction time; reduction potential; complexation time; pH in acetate buffer and phosphate buffer. The modified electrodes were prepared in L solutions (1mM) in acetonitrile (CH3CN) containing tetra n-butyl ammonium perchlorate (0.1 M TBAP) as supporting electrolyte. The electrochemical method includes four main operations: 1) polymeric film formation by controlled potential electrolysis (CPE) at 1.7V using a charge of 1 mC; 2) film conditioning in 0.1 M buffer acetate solution using cyclic voltammetry; 3) 25 min complexation time in a standard solution prepared from lead nitrate (II) using as matrix ultrapure water or a real sample; 4) stripping by differential pulse voltammetry method (DPV) in acetate buffer at pH 4.0, after 120 s reduction time at a reduction potential of -1.0 V. Determination time for a single standard solution or real sample was around 45 min. Evaluation of the method performance parameters (linearity, working range, detection limit, quantification limit, repeatability, and recovery) was done. It confirms that the proposed method is suitable to detect and quantify lead content over 1.2 �g/L in soft water samples.

Measurement and thermodynamic analysis of the acid-base equilibria of two bioactive flavanone glycosides in different temperatures and non-aqueous mixtures

In this research, the acid-base properties of two glycosilated flavanones namely naringoside and hesperidin were thermodynamically studied using spectrophotometric and potentiometric techniques at various temperatures (293.15–313.15) K. Because of very low solubility of these flavanones in aqueous solution, the protonation constants were obtained in ethanol-water mixtures (60–90% v/v) containing 0.10moldm−3 tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte for naringoside and DMSO-water mixed solvents (50–95% v/v) containing 0.10moldm−3 NaCl for hesperidin. Data process for the calculation of the protonation constants was done using the computer program STAR. The thermodynamic quantities (ΔG°, ΔH°, and ΔS°) of the protonation process were obtained by means of modified van't Hoff equation. It was found that the acid dissociation reaction is exothermic and the entropic contribution is low for both the flavanones. Finally, the influence of solute-solvent interactions on the protonation equilibria in various temperatures was modelled using Kamlet, Abboud and Taft (KAT) solvatochromic parameters and Hildebrand's solubility index.

Crystal structure, Hirshfeld surface, physicochemical, thermal and DFT studies of (N1E, N2E)-N1,N2-bis((5-bromothiophen-2-yl)methylene)ethane-1,2-diamine N2S2 ligand and its [CuBr(N2S2)]Br complex

A new tetradentate N2S2 Schiff base ligand derived from 5-bromothiophene-2-carbaldehyde and its [CuBr(N2S2)]Br complex were synthesized in good yield. FT-IR was investigated to monitor the condensation reaction during the ligand synthesis process. The ligand, N2S2, and its complex, [CuBr(N2S2)]Br, complex have been characterized with the aid of several spectroscopic techniques such as UV–vis., MS, FT-IR, EA, EDS, NMR (for N2S2), as well as by thermal (TG/DTG) analysis. In addition, cyclic voltammetry has been employed to examine the redox behavior of [CuBr(N2S2)]Br complex in N,N’-dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium perchlorate (TBAP). The anti-conformation EE isomer of the ligand (N2S2) was confirmed by means of X-ray crystallography; ligand crystallizes in to the monoclinic P21/c space group. N2S2 ligand was subjected to DFT-theoretical calculations and results are consistent with the experimental chemical analysis.

Synthesis, characterization and electrochemistry of dipyrrinato nickel(II) complexes with different aromatic rings to meso-position

Three kinds of dipyrrinato nickel(II) complexes with different aromatic substituted groups on meso-carbon position have been synthesized while their properties have been studied. The aromatic substituents of investigated compounds are phenyl (2a), 2-naphthyl (2b) and 4-carbazolylphenyl (2c), respectively. All compounds were characterized by 1H and 13C NMR spectra, MS and UV–Vis absorption spectra. These compounds were also investigated by electrochemistry in dichloromethane containing 0.1M tetra-n-butylammonium perchlorate (TBAP). Each compound undergoes two reversible reductions along with one irreversible oxidation and 2c shows another two quasi-reversible oxidations. The redox potentials of 2a-c are consistent with the optical spectroscopy data and the relatively narrow HOMO–LUMO gaps that are predicted in DFT calculation. The X-ray crystal structure of 5-(4-carbazolylphenyl) nickel(II) dipyrrinato complex (2c) was also reported.

Synthesis, characterization, and electrochemical behavior of a cobalt(II) salen-like complex

A new tetradentate cobalt(II)–Schiff base complex has been synthesized via the reaction of the ligand 2,2′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(4-((methyl(phenyl)amino)methyl)phenol) with a stoichiometric amount of cobalt(II) acetate tetrahydrate in absolute ethanol. This cobalt(II) complex has been characterized with the aid of several spectroscopic techniques (FT-IR, UV–Vis, and mass spectrometry) as well as by thermal (TGA and DTA) and elemental analysis. Cyclic voltammetry has been employed to examine the redox behavior of the cobalt(II) complex in dimethylformamide (DMF) containing 0.10M tetra-n-butylammonium tetrafluoroborate (TBABF4). In addition, the electrogenerated cobalt(I) form of the complex has been (a) employed as a catalyst for the reduction of 1-iododecane and (b) compared with the behavior of cobalt(I) salen. Finally, the cobalt(II) complex has been subjected to anodic electropolymerization onto the surface of a glassy carbon electrode in DMF containing 0.10M tetra-n-butylammonium perchlorate (TBAP).

Electrochemical and spectroelectrochemical studies of diphosphorylated metalloporphyrins. Generation of a phlorin anion product.

Two series of diphosphoryl-substituted porphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The investigated compounds are 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrins (Ph)2(P(O)(OEt)2)2PorM and 5,15-bis(diethoxyphosphoryl)-10,20-di(para-carbomethoxyphenyl)porphyrins (PhCOOMe)2(P(O)(OEt)2)2PorM where M = 2H, Co(II), Ni(II), Cu(II), Zn(II), Cd(II), or Pd(II). The free-base and five metalated porphyrins with nonredox active centers undergo two ring-centered oxidations and two ring-centered reductions, the latter of which is followed by a chemical reaction of the porphyrin dianion to give an anionic phlorin product. The phlorin anion is electroactive and can be reoxidized by two electrons to give back the starting porphyrin, or it can be reversibly reduced by one electron at more negative potentials to give a phlorin dianion. The chemical conversion of the porphyrin dianion to a phlorin anion proceeds at a rate that varies with the nature of the central metal ion and the solvent. This rate is slowest in the basic solvent pyridine as compared to CH2Cl2 and PhCN, giving further evidence for the involvement of protons in the chemical reaction leading to phlorin formation. Calculations of the electronic structure were performed on the Ni(II) porphyrin dianion, and the most favorable atoms for electrophilic attack were determined to be the two phosphorylated carbon atoms. Phlorin formation was not observed after the two-electron reduction of the cobalt porphyrins due to the different oxidation state assignment of the doubly reduced species, a Co(I) π anion radical in one case and an M(II) dianion for all of the other derivatives. Each redox reaction was monitored by thin-layer UV-visible spectroelectrochemistry, and an overall mechanism for each electron transfer is proposed on the basis of these data.

Electrochemistry and spectroelectrochemistry of β-pyrazino-fused tetraarylporphyrins in nonaqueous media

Bis-porphyrins containing a β,β′-fused pyrazino (Pz) linking group were examined by electrochemistry and thin-layer UV-visible spectroelectrochemistry in PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte. The investigated compounds are represented as M(TPP)-Pz-(TPP)M, where TPP is the dianion of tetraphenylporphyrin and M = Zn(II) , Cu(II) or Ag(II) . The effect of the linking Pz group on the redox potentials and UV-visible spectra of the neutral, electroreduced and electrooxidized bis-porphyrins is discussed and the data compared to what is observed for related monoporphyrins and earlier characterized bis-porphyrins containing a tetraazaanthracene (TA) linking group and the same central metal ions. The Cu(II) and Zn(II) Pz linked bis-porphyrins exhibit a relatively strong interaction between the two equivalent porphyrin macrocycles as evidenced by UV-visible spectra of the neutral compounds and characteristic splitting of redox processes for three of the four electron transfer reactions, the one exception being the first oxidation, where no splitting of potentials is observed in the formation of the bisporphyrin bis-cation radical, [M(TPP)-Pz-(TPP)M]2+. The first oxidation and first reduction of the bis-porphyrin with two Ag(II) central metal ions occurs via two overlapping one-electron transfer steps in each process indicating equivalent, but non-interacting redox centers. This difference in redox behavior is due to differences in the site of electron transfer, metal centered for the Ag(II) bisporphyrins, which undergo Ag(II) / Ag(III) and Ag(II) / Ag(I) processes as compared to only ring centered electron transfers for the Cu(II) and Zn(II) derivatives. The Pz-linked Zn(II) bis-porphyrins have a larger average HOMO–LUMO gap (2.01 V) as compared to related tetraazaanthracene linked bis-porphyrins (1.67 V), which were earlier characterized in the literature, but the gap is smaller than that for the mono-porphyrins with the same central metal ions (2.17 V). Each redox reaction of the investigated bisporphyrins was characterized by thin-layer spectroelectrochemistry.

Effect of solvent and protonation/deprotonation on electrochemistry, spectroelectrochemistry and electron-transfer mechanisms of N-confused tetraarylporphyrins in nonaqueous media.

A series of N-confused free-base meso-substituted tetraarylporphyrins was investigated by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) and added acid or base. The investigated compounds are represented as (XPh)4 NcpH2 , in which "Ncp" is the N-confused porphyrin macrocycle and X is a OCH3 , CH3 , H, or Cl substituent on the para position of each meso-phenyl ring of the macrocycle. Two distinct types of UV/Vis spectra are initially observed depending upon solvent, one corresponding to an inner-2H form and the other to an inner-3H form of the porphyrin. Both forms have an inverted pyrrole with a carbon inside the cavity and a nitrogen on the periphery of the π-system. Each porphyrin undergoes multiple irreversible reductions and oxidations. The first one-electron addition and first one-electron abstraction are located on the porphyrin π-ring system to give π-anion and π-cation radicals with a potential separation of 1.52 to 1.65 V between the two processes, but both electrogenerated products are unstable and undergo a rapid chemical reaction to give new electroactive species, which were characterized in the present study. The effect of the solvent and protonation/deprotonation reactions on the UV/Vis spectra, redox potentials and reduction/oxidation mechanisms is discussed with comparisons made to data and mechanisms for the structurally related free-base corroles and porphyrins.

Synthesis, structures, and properties of lantern-type dinuclear ruthenium(II,III) complexes cis-[Ru2{3,5-(CF3)2-pf}2(O2CMe)2Cl] and [Ru2{3,5-(CF3)2-pf}3(O2CMe)Cl], 3,5-(CF3)2-pf− = N,N′-bis[3,5-bis(trifluoromethyl)phenyl]formamidinate anion

Lantern-type dinuclear complexes, cis-[Ru2{3,5-(CF3)2-pf}2(O2CMe)2Cl] and [Ru2{3,5-(CF3)2-pf}3(O2CMe)Cl] (3,5-(CF3)2-pf−=N,N′-bis[3,5-bis(trifluoromethyl)phenyl]formamidinate anion), were prepared and characterized. The cis-(2:2) and (3:1) arrangements of the formamidinate and acetate bridging ligands around the Ru25+ core were confirmed by the X-ray crystal analysis as well as 1H and 19F NMR spectra (measured at 25°C in CD2Cl2), where paramagnetic shifts were observed for the signals due to the unpaired electrons in the dinuclear core. Variable-temperature magnetic moments (2–300K) showed the existence of three unpaired electrons in the dinuclear units with the large D values (60cm−1 for the cis-(2:2) Ru25+ complex and 50cm−1 for the (3:1) Ru25+ complex). The electronic state with S=3/2 was also ascertained by the EPR spectra measured in solid at 4K and in frozen toluene/dichloromethane solution at 15K, absorption spectra in dichloromethane and cyclic voltammograms (CVs) in THF using tetra-n-butyl ammonium perchlorate (TBAP) as electrolyte.

Cobalt triarylcorroles containing one, two or three nitro groups. Effect of NO2 substitution on electrochemical properties and catalytic activity for reduction of molecular oxygen in acid media

Cobalt(III) triarylcorroles containing 0–3 nitro groups on the para-position of the three meso-phenyl rings of the macrocycle were synthesized and characterized by electrochemistry, mass spectrometry, (UV–vis) and 1H NMR spectroscopy. The examined compounds are represented as (NO2Ph)nPh3−nCorCo(PPh3), where n varies from 0 to 3 and Cor represents the core of the corrole. Each compound can undergo two metal-centered one-electron reductions leading to formation of Co(II) and Co(I) derivatives in CH2Cl2 or pyridine containing 0.1M tetra-n-butylammonium perchlorate (TBAP). A stepwise two electron reduction of each NO2Ph group of the compound is also observed. The first is reversible and occurs in a single overlapping step at the same potential which involves an overall one-, two- or three-electron transfer process for compounds 2–4, respectively. This indicates the lack of an interaction between these redox active sites on the corroles. The second reduction of the NO2Ph groups is irreversible and located at a potential which overlaps the Co(II)/Co(I) process of the compounds. Thin-layer UV–visible spectroelectrochemical measurements in CH2Cl2, 0.1M TBAP demonstrate the occurrence of an equilibrium between a Co(III) π-anion radical and a Co(II) derivative with an uncharged macrocycle after the first controlled potential reduction of the nitro-substituted corroles. All four cobalt corroles were also examined as catalysts for the electroreduction of O2 when coated on an edge-plane pyrrolytic graphite electrode in 1.0M HClO4. This study indicates that the larger the number of nitro-substituents on the cobalt corrole, the better the compound acts as a catalyst.

Electrochemistry of Fe(IV) and Mn(IV) corroles containing meso-dichlorophenyl substituents and the use of these compounds as catalysts for the electroreduction of dioxygen in acid media

Two meso-dichlorophenyl substituted metallocorroles were synthesized and characterized as to their elec- trochemical and spectroelectrochemical properties in dichloromethane, benzonitrile, and pyridine containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte. The examined compounds are represented as (Cl2Ph)3CorFe IV Cl and (Cl2Ph)3CorMn IV Cl where (Cl2Ph)3Cor is the trianion of 5,10,15-tri(2,4-dichlorophenyl)cor- role. Each metallocorrole was examined as to its catalytic activity for the electoreduction of dioxygen when coated on an edge-plane pyrolytic graphite electrode in 1.0 M HClO4. Cyclic voltammetry combined with linear sweep voltammetry at a rotating disk electrode (RDE) and a rotating ring disk electrode (RRDE) was utilized to evaluate the catalytic activity for the electroreduction of O2. The main O2 reduction product is hydrogen peroxide under the given experimental

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry, Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

A series of planar and nonplanar free-base β-pyrrole substituted meso-tetraarylporphyrins were characterized by electrochemistry, spectroelectrochemistry, and protonation or deprotonation reactions in neutral, acidic, and basic solutions of CH2 Cl2 . The neutral compounds are represented as H2 (P), in which P represents a porphyrin dianion with one of several different sets of electron-withdrawing or -donating substituents at the messo and/or β-pyrrole positions of the macrocycle. The conversion of H2 (P) to [H4 (P)](2+) in CH2 Cl2 was accomplished by titration of the neutral porphyrin with trifluoroacetic acid (TFA) while the progress of the protonation was monitored by UV/Vis spectroscopy, which was also used to calculate logβ2 for proton addition to the core nitrogen atoms of the macrocycle. Cyclic voltammetry was performed after each addition of TFA or TBAOH to CH2 Cl2 solutions of the porphyrin and half-wave potentials for reduction were evaluated as a function of the added acid or base concentration. Thin-layer spectroelectrochemistry was used to obtain UV/Vis spectra of the neutral and protonated or deprotonated porphyrins under the application of an applied reducing potential. The magnitude of the protonation constants, the positions of λmax in the UV/Vis spectra and the half-wave or peak potentials for reduction are then related to the electronic properties of the porphyrin and the data evaluated as a function of the planarity or nonplanarity of the porphyrin macrocycle. Surprisingly, the electroreduction of the diprotonated nonplanar porphyrins in acid media leads to H2 (P), whereas the nonplanar H2 (P) derivatives are reduced to [(P)](2-) in CH2 Cl2 containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). Thus, in both cases an electrochemically initiated deprotonation is observed.

Electrochemical reduction of phthalide at carbon cathodes in dimethylformamide: Effects of supporting electrolyte and gas chromatographic injector-port chemistry on the product distribution

Abstract Cyclic voltammetry and controlled-potential (bulk) electrolysis have been used to investigate the direct reduction of phthalide at carbon electrodes in dimethylformamide (DMF) containing 0.10 M tetramethylammonium perchlorate (TMAP) or tetra- n -butylammonium perchlorate (TBAP). Cyclic voltammograms recorded with a glassy carbon electrode exhibit a single cathodic peak and a corresponding anodic peak that arise, respectively, from one-electron reduction of phthalide to generate a radical-anion intermediate and from reoxidation of the intermediate. At a scan rate of 100 mV s −1 , quasi-reversible behavior is observed (due to ring-opening of the radical-anion), whereas fully reversible behavior is seen at 5 V s −1 or higher. Digital simulation of cyclic voltammograms indicates that the lifetime of the radical-anion is 3.5 s. Bulk electrolysis of phthalide at a reticulated vitreous carbon cathode affords products that depend on the procedure used to analyze the catholyte. Direct injection of catholyte into a gas chromatograph shows phthalide and a 2-methylbenzoate ester bearing an alkyl moiety from the supporting-electrolyte cation. However, if the catholyte is partitioned between diethyl ether and aqueous hydrochloric acid before gas chromatographic analysis, phthalide and 2-methylbenzoic acid are observed. Thermally induced reactions that occur in the injector port of the gas chromatograph are responsible for the formation of the 2-methylbenzoate ester as well as for the phthalide found in all electrolyzed solutions.

Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(iii,ii) complex with an unusual arrangement of the bridging ligands

A mixed-ligand metal-metal bonded diruthenium complex having the formula Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl where ap is the anilinopyridinate anion was synthesized from the reaction of Ru(2)(O(2)CCH(3))(4)Cl and H(2,4,6-(CH(3))(3)ap), after which the isolated product was structurally, spectroscopically and electrochemically characterized. The crystal structure reveals an unusual arrangement of the bridging ligands around the dimetal unit where one ruthenium atom is coordinated to one anilino and two pyridyl nitrogen atoms while the other ruthenium atom is coordinated to one pyridyl and two anilino nitrogen atoms. To our knowledge, Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl is the only example of a mixed-ligand diruthenium complex of the type [Ru(2)L(3)(O(2)CCH(3))](+), where L is an unsymmetrical anionic bridging ligand that has been structurally characterized with a "(2,1)" geometric conformation of the bridging ligands, all others being "(3,0)". The initial Ru(2)(5+) compound in CH(2)Cl(2) or CH(3)CN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) undergoes up to four one-electron redox processes involving the dimetal unit. The Ru(2)(5+/4+) and Ru(2)(5+/6+) processes were characterized under N(2) using thin-layer UV-visible spectroelectrochemistry and this data is compared to UV-visible spectral changes obtained during similar electrode reactions for related diruthenium compounds having the formula Ru(2)L(4)Cl or Ru(2)L(3)(O(2)CCH(3))Cl where L is an anionic bridging ligand. Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl was also examined by UV-visible and FTIR spectroelectrochemistry under a CO atmosphere and two singly reduced Ru(2)(4+) species, [Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO)Cl](-) and Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO) were in situ generated for further characterization. The CO-bound complexes could be further reduced and exhibited additional reductions to their Ru(2)(3+) and Ru(2)(2+) oxidation states.

Electroreduction and Acid–Base Properties of Dipyrrolylquinoxalines

The electroreduction and acid-base properties of dipyrrolylquinoxalines of the form H(2)DPQ, H(2)DPQ(NO(2)), and H(2)DPQ(NO(2))(2) were investigated in benzonitrile (PhCN) containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). This study focuses on elucidating the complete electrochemistry, spectroelectrochemistry, and acid-base properties of H(2)DPQ(NO(2))(n) (n = 0, 1, or 2) in PhCN before and after the addition of trifluoroacetic acid (TFA), tetra-n-butylammonium hydroxide (TBAOH), tetra-n-butylammonium fluoride (TBAF), or tetra-n-butylammonium acetate (TBAOAc) to solution. Electrochemical and spectroelectrochemical data provide support for the formation of a monodeprotonated anion after disproportionation of a dipyrrolylquinoxaline radical anion produced initially. The generated monoanion is then further reduced in two reversible one-electron-transfer steps at more negative potentials in the case of H(2)DPQ(NO(2)) and H(2)DPQ(NO(2))(2). Electrochemically monitored titrations of H(2)DPQ(NO(2))(n) with OH(-), F(-), or OAc(-) (in the form of TBA(+)X(-) salts) give rise to the same monodeprotonated H(2)DPQ(NO(2))(n) produced during electroreduction in PhCN. This latter anion can then be reduced in two additional one-electron-transfer steps in the case of H(2)DPQ(NO(2)) and H(2)DPQ(NO(2))(2). Spectroscopically monitored titrations of H(2)DPQ(NO(2))(n) with X(-) show a 1:2 stoichiometry and provide evidence for the production of both [H(2)DPQ(NO(2))(n)](-) and XHX(-). The spectroscopically measured equilibrium constants range from log β(2) = 5.3 for the reaction of H(2)DPQ with TBAOAc to log β(2) = 8.8 for the reaction of H(2)DPQ(NO(2))(2) with TBAOH. These results are consistent with a combined deprotonation and anion binding process. Equilibrium constants for the addition of one H(+) to each quinoxaline nitrogen of H(2)DPQ, H(2)DPQ(NO(2)), and H(2)DPQ(NO(2))(2) in PhCN containing 0.1 M TBAP were also determined via electrochemical and spectroscopic means; this gave rise to log β(2) values ranging from 0.7 to 4.6, depending upon the number of nitro substituents present on the H(2)DPQ core. The redox behavior of the H(2)DPQ(NO(2))(n) compounds of the present study were further analyzed through comparisons with simple quinoxalines that lack the two linked pyrrole groups, i.e., Q(NO(2))(n) where n = 0, 1, or 2. It is concluded that the pyrrolic substituents play a critical role in regulating the electrochemical and spectroscopic features of DPQs.

Unusual Multi-Step Sequential AuIII/AuII Processes of Gold(III) Quinoxalinoporphyrins in Acidic Non-Aqueous Media

The electrochemistry of gold(III) mono- and bis-quinoxalinoporphyrins was examined in CH(2)Cl(2) or PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) before and after the addition of trifluoroacetic acid to solution. The investigated porphyrins are represented as Au(PQ)PF(6) and Au(QPQ)PF(6), where P is the dianion of the 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin and Q is a quinoxaline group fused to a β,β'-pyrrolic position of the porphyrin macrocycle; in Au(QPQ)PF(6) there is a linear arrangement where the quinoxalines are fused to pyrrolic positions that are opposite each other. The porphyrin without the fused quinoxaline groups, Au(P)PF(6), was also investigated under the same solution conditions. In the absence of acid, all three gold(III) porphyrins undergo a single reversible Au(III)/Au(II) process leading to the formation of a Au(II) porphyrin which can be further reduced at more negative potentials to give stepwise the Au(II) porphyrin π-anion radical and dianion, respectively. However, in the presence of acid, the initial Au(III)/Au(II) processes of Au(PQ)PF(6) and Au(QPQ)PF(6) are followed by an internal electron transfer and protonation to regenerate new Au(III) porphyrins assigned as Au(III)(PQH)(+) and Au(III)(QPQH)(+). Both protonated gold(III) quinoxalinoporphyrins then undergo a second Au(III)/Au(II) process at more negative potentials. The electrogenerated monoprotonated monoquinoxalinoporphyrin, Au(II)(PQH), is then further reduced to its π-anion radical and dianion forms, but this is not the case for the monoprotonated bis-quinoxalinoporphyrin, Au(II)(QPQH), which accepts a second proton and is rapidly converted to Au(III)(HQPQH)(+) before undergoing a third Au(III)/Au(II) process to produce Au(II)(HQPQH) as a final product. Thus, Au(P)PF(6) undergoes one metal-centered reduction while Au(PQ)PF(6) and Au(QPQ)PF(6) exhibit two and three Au(III)/Au(II) processes, respectively. These unusual multistep sequential Au(III)/Au(II) processes were monitored by thin-layer spectroelectrochemistry and a reduction/oxidation mechanism for Au(PQ)PF(6) and Au(QPQ)PF(6) in acidic media is proposed.

Electrochemical and spectroscopic studies of poly(diethoxyphosphoryl)porphyrins

The synthesis and electrochemical characterization of two related series of porphyrins bearing diethoxyphosphoryl groups are reported. One group of compounds is represented as (T( p-R)PP)M where R = phos = P(O)(OEt) 2 and M = Zn(II) or H 2 while the other is represented as (di( p-R)Pdi(phos)P)M where R = P(O)(OEt) 2, H or CH 3 and M = Zn(II) or H 2. Each porphyrin was investigated by electrochemistry and thin-layer spectroelectrochemistry in CH 2Cl 2, CDCl 3, CHCl 3 or PhCN containing tetra- n-butylammonium perchlorate (TBAP) as supporting electrolyte. The highly electron-withdrawing P(O)(OEt) 2 groups lead to easier reductions and harder oxidations than the two comparison compounds, (TPP)Zn and (TPP)H 2 where TPP = the dianion of the tetraphenylporphyrin. The P(O)(OEt) 2 groups located on the two meso-positions of the porphyrin macrocycle in (di( p-R)Pdi(phos)P)M or on the para-positions of the substituted phenyl groups in (T( p-R)PP)M can also bind to the Zn(II) ion of another porphyrin in solution, leading to the formation of aggregates which was both concentration and solvent dependent as determined by UV–visible spectroscopy and electrochemistry. Binding constants for addition of triphenylphosphine oxide (PPh 3O) to the zinc porphyrins were also measured in CDCl 3 and ranged from log K = 1.7 to 3.1 for formation of the five-coordinate complex. The comparison of X-ray diffraction data for the investigated diethoxyphosphoryl-substituted porphyrin (diPdi(phos)P)H 2 and its Zn complex showed that the metallation induces almost no change in the geometry of the porphyrin macrocycle, but plays the key role in the process of supramolecular assembling.