Paul-Louis Fabre

Automatic ir drop correction for studies of electrochemical systems

Abstract The interest of automatic ir drop correction by the interrupt method is evaluated by carrying out electrochemical studies on ferrocene in various non-aqueous solvents, using a home-made microcomputer-controlled potentiostat. Special attention is devoted to voltammetry and cyclic voltammetry.

Spectroelectrochemical behaviour in dimethylformamide of pseudo-oxocarbons dianions derived from the croconate dianion

Abstract The electrochemical behaviour of croconate dianion and dicyanomethylene-substituted croconate dianions was investigated in dimethylformamide containing tetrabutylammonium hexafluorophosphate at a Pt electrode. By cyclic voltammetry, the oxidation of these dianions involves two successive reversible monoelectronic transfers which yield the corresponding radical-anions and neutral species. By reduction of these dianions, the radical-trianions are characterized by uv-vis and esr spectroscopies but are unstable. The redox potentials are strongly dependent on the number of dicyanomethylene groups. Electrochemical kinetics parameters have been determinated. Among the different oxidation states, only the dianions and radical-anions are stable. Due to their high absorption in the uv-visible domain, spectroelectrochemical studies have been carried out to characterize the redox states. The radical-anion/dianion redox couple is sufficiently cyclable for electromodulated colour changes and may be used in electrochromic applications.

Complexation of croconate violet with copper(II). Crystal structures, spectroscopic characterizations and redox studies

Abstract The crystal structures of two copper(II) complexes of croconate violet (3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate=L2−) have been determined by X-ray methods. Complex 1 consists of mononuclear [CuL2(H2O)2]2− ions, potassium cations and two crystallisation water molecules. Complex 2 consists of mononuclear [CuL3]4− ions, (NBu4)+ cations and one half crystallisation water molecule. In these two complexes, the ligand is coordinated in a chelating mode by two adjacent oxygen atoms. The electrochemical behaviour of these complexes is discussed and compared to that of the free croconate violet.

Interactions of squaric and croconic acids with [PtL4]2+ complexes (L = NH3, L2 = ethylenediamine): oxidative properties of oxocarbon acids and crystal structure determinations

Squaric (H2Sq) and croconic (H2Croc) acid (H2A) react with [PtL4]2+ (L = ammonia or L2 = ethylenediamine) to yield complexes formulating as [PtL4](HA)2. The crystal structure of the complexes [Pt(en)2](HSq)2 and [Pt(en)2](HCroc)2 have been determined using X-ray diffraction techniques. Oxidation of platinum occurred in the course of the same reaction and complexes of [PtL4Cl2]A were obtained. The X-ray determination of the structure of [Pt(NH3)4Cl2]Sq is reported. Electrochemical measurements have been performed in the solid state to support the results obtained during the oxidation process.

Pseudo-oxocarbon complexes — crystal structure of a copper(II) complex with 2,4-bis(dicyanomethylene)cyclobutane-1,3-dione

Abstract The reaction of copper(II) ions with the 2,4-bis(dicyanomethylene)cyclobutane-1,3-dione dianion (2,4-dcmsq2−), a pseudo-oxocarbon derived from squaric acid in which two carbonyl oxygen atoms have been substituted by dicyanomethylene groups C(CN)2, leads to many complexes according to the preparative scheme. The complex [Cu(2,4-dcmsq)(H2O)4]n has been synthesized and characterized by single-crystal X-ray diffraction. The structure consists of a chain of copper atoms bridged by the ligand with short CuN bonds. Spectroscopic and structural characterizations of the product are compared with those of the previously described [Cu(2,4-dcmsq)(H2O)4·2H2O]n.

Electrochemical Studies of the Formation Mechanism of (cation) x [Ni(dmit)2 Conductive Compounds and of their Non-Integer Oxidation State

Abstract The mechanism of electrocrystallization of (cation) x [Ni(dmit)2 (cation = NHMe+ 3, NMe+ 4) conductive compounds is studied under non-stationary conditions by cyclic voltammetry using ultramicroelectrodes at high potential-scan rates. It is shown that the formation of non-integer oxidation state compounds proceeds through one-electron transfers combined with chemical reaction between [Ni(dmit)2 − and [Ni(dmit)2 0 electrogenerated species exhibiting integer charges. The non-integer oxidation state in (cation) x [Ni(dmit)2 compounds (cation = NBu+ 4, AsPh+ 4, NH2Me+ 2, NH3Me+), measured by the non-integer value of x, is determined under stationary conditions by use of the carbon paste electrode at very low potential-scan rates.

Preparation and crystal structure of trans-diazidotetrakis(trimethylphosphine)ruthenium(II)

Abstract The novel trimethylphosphine azido ruthenium(II) complex trans -Ru(N 3 ) 2 (PMe 3 ) 4 has been obtained and characterized by elemental analysis, IR and NMR spectroscopies, and electrochemistry. Its structure has been determined by single crystal X-ray diffraction methods. The complex consists of monomeric Ru(N 3 ) 2 (PMe 3 ) 4 units, in which the coordination geometry around the Ru atom is a distorted octahedron. The two azido ligand occupy trans positions and are oriented in two nearly orthogonal planes. Conversion into the cis isomer in CH 2 Cl 2 has been followed by 31 P NMR and cyclic voltammetry.

Electrochemical studies of Iron(III) Schiff base complexes—I. The monomeric FeIII(N2O2)Cl complexes

Abstract The electrochemical reduction of Fe III (L)Cl, where L is a Schiff base, has been investigated in aprotic solvents by cyclic voltammetry and coulometry with UV-vis spectroscopy. Six complexes derived from Schiff base ligands with N 2 O 2 environments are described. The reduction of Fe III (L)Cl into Fe II (L)Cl occurs at a potential around −0.5 V vs S.C.E. through an EC mechanism where the following reaction concerns the decomposition of iron(II), a highly reactive complex. A high electronic delocalization of the Schiff base, such as in SALOPH, stabilizes the oxidation state II of iron and shifts the redox potential anodically. The study reveals the extreme reactivity of iron(II) towards dioxygen. Traces of dioxygen with Fe II (L)Cl yield the μ-oxo bridged Fe III dimers (L)FeOFe(L), whose reduction potentials lie around −1 V vs S.C.E. The redox couple Fe II (L)/Fe III (L) is potentially a good electrochemical mediator for redox catalysis.

Electrochemical studies of iron(III) Schiff base complexes—II. Dimeric μ-OXO[FeIII(N2O2)]2O complexes

Abstract The electrochemical reduction of μ-oxo bridged Fe III dimers (L)FeOFe(L), where L is a Schiff base, has been investigated in aprotic solvents by cyclic voltammetry and coulometry with UV-vis spectroscopy. Three complexes deriving from Schiff base ligands with N 2 O 2 environments are described. The reduction of (L)Fe III OFe III (L) occurs at a potential around −1 V/SCE and releases the monomeric Fe II (L) complex. A mechanism is proposed using high speed cyclic voltammetry. The reduction pattern is affected by dioxygen through the high reactivity of Fe II (L). These μ-oxo bridged Fe III dimers (L)FeOFe(L) can also be cleaved by Cl − addition and yield the monomeric Fe III (L) complexes. Finally, the FeO bond is not so strong because it cleaves either by electrochemical reduction or by chemical addition of Cl − .

EPR spectroelectrochemical investigation of guanine radical formation and environment effects.

Guanine radical detection was carried out by a new convenient and efficient method coupling electron paramagnetic resonance spectroscopy and indirect electrooxidation of guanine in different biological environments, from the free nucleotide to several types of DNA substrates. Compared to the widely used photoirradiation method, this method appeared more selective in the choice of the electrochemical mediator. Carried out in presence of a ruthenium mediator and PBN as spin trap, this method revealed two types of EPR spectra depending of the environment of the guanine radical. Both EPR spectra show the trapping of the neutral guanine radical G(-H)(•) obtained after fast deprotonation of the radical cation G(•+). However, they differ by the atom where the trapped radical is centered. This difference highlights the structural dependency of the environment on the nature of the radical formed. This work gave the evidence of an innovative method to detect in situ the guanine radical.