The Pt‐Organometallic Version of Perigraniline: Going Blue

Four conjugated push–pull organometallic polymers ( [Pt]‐AQ )_n ( [Pt] = trans‐bis(phenylacetylene)bis(tributylphosphine)platinum(II); AQ = 2‐bromo‐, 2,6‐dibromo‐, 2,6‐diamino‐, and unsubstituted anthraquinone diimine) were prepared and characterized by UV–vis spectroscopy and electrochemistry. A low‐energy charge transfer, CT, band ( [Pt] *→ AQ ; confirmed by density functional theory calculations), was found in the 445–500 nm window rather than the expected red‐shifted range above 630 nm. X‐ray structures of four model compounds reveal that steric hindrance induces large dihedral angles between the C₆H₄ and NCC₂ planes, rendering π‐orbital overlap difficult between the [Pt] and AQ units. The position of the CT band is mainly driven the reduction potential of the anthraquinone diimine unit.     

Aqueous electrochemistry of poly(vinylanthraquinone) for anode-active materials in high-density and rechargeable polymer/air batteries

A layer of poly(2-vinylanthraquinone) on current collectors underwent reversible electrode reaction at -0.82 V vs Ag/AgCl in an aqueous electrolyte. A repeatable charging/discharging cycles with a redox capacity comparable to the formula weight-based theoretical density at the negative potential suggested that all of the anthraquinone pendants in the layer was redox-active, that electroneutralization by an electrolyte cation was accomplished throughout the polymer layer, and that the layer stayed on the current collector without exfoliation or dissolution into the electrolyte during the electrolysis. The charging/discharging behavior of the polymer layer in the aqueous electrolyte revealed the capability of undergoing electrochemistry even in the nonsolvent of the pendant group, which offered insight into the nature of the anthraquinone pendants populated on the aliphatic chain. Charging/discharging capability of air batteries was accomplished by using the polymer layer as an organic anode-active material. A test cell fabricated using the conventional MnO(2)/C cathode catalyst exhibited a discharging voltage at 0.63 V corresponding to their potential gap and a charging/discharging cycle of more than 500 cycles without loss of the capacity.     

Naphthobipyrrole: versatile synthesis and electropolymerization

A facile synthetic route to a new polycyclic pyrrole derivative, 3,8-diethyl-1,10-dihydro-benzo[e]pyrrolo[3,2-g]indole (1), is reported. This annulated bipyrrole acts as a monomer for electropolymerization and forms an electrochromic conducting polymer (poly1) when electrooxidized at low potentials (0.4 V vs Ag/Ag(+)) in acetonitrile. The presence of alkyl substituents at the 3 and 8 carbons (β-pyrrolic positions) induces regioselective 2,5'-coupling of the pyrrole repeat units and gives rise to the more uniform polymeric product, poly1. Poly1 exhibits globular morphology, as judged from SEM pictures. Its spectroelectrochemical features can be attributed to the formation of four possible states: neutral, polaron, bipolaron, and transverse bipolaron. The relatively low switching potentials (-0.6 to +0.9 V vs Ag/Ag(+) in MeCN) displayed by poly1 leads us to suggest that 1 has a role to play as a polymerizable moiety for the development of multicolor electrochromic materials.     

UV-Vis and Raman Spectral Analysis of Polyaniline/Gold Thin Films as a Function of Applied Potential

Polyaniline and polyaniline/gold films were prepared by potentiodynamic oxidation of aniline in 1 M H₂SO₄ aqueous solution, and their electrochromic properties were investigated by UV-Vis and Raman spectroscopy. Both tetrachloroaurate and gold nanoparticles were used to deposit gold onto or inside the polyaniline film based on the deposition technique used. Polyaniline films showed multiple color changes (blue to green to yellow) depending on the electrochemical reactions in the potential range ?0.2 to 0.8 V vs. Ag/AgCl. The color of polyaniline films changed from transparent green to yellow at the anodic peak around 0.2 V and gradually changed from green to dark blue at potentials higher than 0.5 V. The deterioration of electrochromic properties is caused by hydrolysis of the diimine structure formed by oxidation at 0.8 V. Furthermore, the polyaniline films showed enhanced Raman characteristics (due to SERS) depending on the treatments with gold and the potentials applied to the films to control the oxidation state.     

Luminescent heterotrinuclear complexes with Pt(diimine)(dithiolate) and metal diphosphine as components

Reactions of Pt(diimine)(tdt) (tdt =3,4-toluenedithiolate) with [M(2)(dppm)(2)(MeCN)(2)](2+) (M = Cu(I) or Ag(I), dppm = bis(diphenylphosphino)methane) gave heterotrinuclear complexes [PtCu(2)(tdt)(mu-SH)(dppm)(3)](ClO(4)) (1) and [PtCu(2)(diimine)(2)(tdt)(dppm)(2)](ClO(4))(2) (diimine = 2,2'-bpyridine (bpy) 2; 4,4'-dimethyl-2,2'-bipyridine (dmbpy) 3; phenanthroline (phen) 4, 5-bromophenanthroline (Brphen) 5) for M = Cu(I), but [PtAg(2)(tdt)(mu-SH)(dppm)(3)](SbF(6)) (6) and [PtAg(2)(diimine)(tdt)(dppm)(2)](SbF(6))(2) (diimine = bpy 7; dmbpy 8; phen 9; Brphen 10) for M = Ag(I). While the complexes [PtAg(2)(diimine)(tdt)(dppm)(2)](SbF(6))(2) (7-10) result from linkage of Pt(diimine)(tdt) and [M(2)(dppm)(2)(MeCN)(2)](2+) by tdt sulfur donors, formation of [PtCu(2)(diimine)(2)(tdt)(dppm)(2)](ClO(4))(2) (2-5) is related to rupture of metal-ligand bonds in the metal components and recombination between the ligands and the metal atoms by self-assembly. The formation of 1 and 6 is involved not only in dissociation and recombination of the metal components, but also in disruption of C-S bonds in the dithiolate (tdt). The dithiolate tdt adopts a chelating and bridging coordination mode in anti conformation for [PtCu(2)(diimine)(2)(tdt)(dppm)(2)](ClO(4))(2) (2-5), whereas there is the syn conformation for other complexes. Compounds 1 and 6 represent sparse examples of mu-SH-bridged heterotrinuclear Pt(II)M(I)(2) complexes, in which Pt(II)-M(I) centers are bridged by dppm and sulfur donors of tdt, whereas M(I)-M(I) (M = Cu for 1; Ag for 6) centers are linked by dppm and the mu-SH donor. The (31)P NMR spectra show typical platinum satellites (J(Pt-P) = 1450-1570 Hz) for 1-6 and Ag-P coupling for Pt(II)-Ag(I) (J(Ag-P) = 350-450 Hz) complexes 6-10. All of the complexes show intense emission in the solid state and in frozen glasses at 77 K. The complexes [PtAg(2)(diimine)(tdt)(dppm)(2)](SbF(6))(2) (7-10) also afford emission in fluid acetonitrile solutions at room temperature. Solid-state emission lifetimes at room temperature are in the microsecond range. It is revealed that emission energies of the trinuclear heterometallic complexes [PtAg(2)(diimine)(tdt)(dppm)(2)](SbF(6))(2) (7-10) exhibit a remarkable blue shift (0.10-0.35 eV) relative to those of the precursor compounds Pt(diimine)(tdt). The crystal structures of 1, 2, 4, 6, 8, and 9 were determined by X-ray crystallography.     

Syntheses, characterization, and luminescence of Pt II-M I (M = Cu, Ag, Au) heterometallic complexes by incorporating Pt(diimine)(dithiolate) with [M2(dppm)2]2+ (dppm = Bis(diphenylphosphino)methane)

Reaction of Pt(diimine)(edt) (edt = 1,2-ethanedithiolate) with M(2)(dppm)(2)(MeCN)(2)(2+) (dppm = bis(diphenylphosphino)methane) gave heterotrinuclear complexes [PtCu(2)(edt)(mu-SH)(dppm)(3)](ClO(4)) (11) and [PtCu(2)(diimine)(2)(edt)(dppm)(2)](ClO(4))(2) (diimine = 2,2'-bpyridine (bpy), 12; 4,4'-dibutyl-2,2'-bipyridine (dbbpy), 13; phenanthroline (phen), 14; 5-bromophenanthroline (brphen), 15) when M = Cu(I). The reaction, however, afforded tetra- and trinuclear complexes [Pt(2)Ag(2)(edt)(2)(dppm)(2)](SbF(6))(2) (17) and [PtAu(2)(edt)(dppm)(2)](SbF(6))(2) (21) when M = Ag(I) and Au(I), respectively. The complexes were characterized by elemental analyses, electrospray mass spectroscopy, (1)H and (31)P NMR, IR, and UV-vis spectrometry, and X-ray crystallography for 14, 17, and 18. The Pt(II)Cu(I)(2) heterotrinuclear complexes 11-15 exhibit photoluminescence in the solid states at 298 K and in the frozen acetonitrile glasses at 77 K. It is likely that the emission originates from a ligand-to-metal charge transfer (dithiolate-to-Pt) (3)[p(S) --> d(Pt)] transition for 11 and from an admixture of (3)[d(Cu)/p(S)-pi(diimine)] transitions for 12-16. The Pt(II)(2)Ag(I)(2) heterotetranuclear complexes 17 and 18 are nonemissive in the solid states and in solutions at 298 K but show photoluminescence at 77 K. The Pt(II)Au(I)(2) heterotrinuclear complexes 19-21, however, are luminescent at room temperature in the solid state and in solution. Compounds 19 and 20 afford negative solvatochromism associated with a charge transfer from an orbital of a mixed metal/dithiolate character to a diimine pi orbital.     

Silver nanoparticle decorated poly(2-aminodiphenylamine) modified carbon paste electrode as a simple and efficient electrocatalyst for oxidation of formaldehyde

This work describes the promising activity of silver nanoparticles on the surface of a poly(2-amino diphenylamine) modified carbon paste electrode (CPE) towards formaldehyde oxidation. Electrodeposition of the conducting polymer film on the CPE was carried out using consecutive cyclic voltammetry in an aqueous solution of 2-aminodiphenylamine and HCl. Nitrogen groups in the polymer backbone had a Ag ion accumulating effect, allowing Ag nanoparticles to be electrochemically deposited on the surface of the electrode. The electrochemical and morphological characteristics of the modified electrode were investigated. The electro-oxidation of formaldehyde on the surface of electrode was studied using cyclic voltammetry and chronoamperometry in aqueous solution of 0.1 mol/L NaOH. The electro-oxidation onset potential was found to be around -0.4 V, which is unique in the literature. The effect of different concentrations of formaldehyde on the electrocatalytic activity of the modified electrode was investigated. Finally, the diffusion coefficient of formaldehyde in alkaline media was calculated to be 0.47 × 10^-6 cm²/s using chronoamperometry.     

Electrochemistry and electrogenerated chemiluminescence of all-trans conjugated polymer poly[distyrylbenzene-b-(ethylene oxide)]s

The electrochemistry and electrogenerated chemiluminescence (ECL) of two linear, stereoregular, and structurally defined PPV derivatives, poly[distyrylbenzene-b-(ethylene oxide)]s, with respective 12 and 16 of ethylene oxide repeat units in the backbone, abbreviated as DE-1 and DE-2, have been studied on glassy carbon and Pt electrodes in CH2Cl2 and CH3CN containing 0.10 M tetra-n-butylammonium perchlorate (TBAP). In CH2Cl2, a one-electron transfer, reversible oxidation at approximately 0.75 V vs Ag/Ag+ (10 mM AgNO3 in CH3CN) was observed for both polymers. Porous polymer films were electrochemically formed on the electrode with multiple cyclic potential scanning. Cast films of DE-1 and DE-2 on the electrode prepared from 1.0 mM of the corresponding CH2Cl2 solutions were used for studies in CH3CN containing 0.10 M TBAP due to their limited solubility in the solvent. A film-type of oxidation was found at approximately 0.80 V vs Ag/Ag+ in CH3CN when a scan rate of less than 1 V/s was used. The soluble oxidation product can be captured and reduced and then reoxidized in solution-phase at the electrode at a relatively high scan rate of, e.g., 2 V/s. ECL responses with a maximum emission at approximately 1.10 V vs Ag/Ag+ were obtained with the cast films in CH3CN (0.10 M TBAP) in the presence of 43 mM tri-n-propylamine (TPrA) after both TPrA and film were oxidized. The ECL is believed to be resulted from the interaction between the oxidized polymer species and the strong reducing TPrA free radical (TPrA*) generated after the deprotonation of TPrA*+ cation species.     

The Ag2O-V2O5-HF((aq)) system and crystal structure of alpha-Ag3VO4

Reactions between the three components Ag2O, V2O5, and HF(aq) were investigated under hydrothermal conditions, and the recovered phases were, in increasing Ag:V content, Ag2V4O11, beta-AgVO3, Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. A higher ratio of Ag2O to V2O5, as compared to a stoichiometric ratio, was required to synthesize Ag4V2O6F2, Ag4V2O7, and alpha-Ag3VO4. Owing to their solubility differences, the crystallization regions are not centered around the respective 2:1 and 3:1 Ag2O/V2O5 tie-lines but rather are centered along the 4:1 and 8:1 Ag2O/V2O5 tie-lines. Reactions with a 4:1 Ag/V ratio either resulted in Ag4V2O6F2 at 150 degrees C or Ag4V2O7 at 200 degrees C. Products were recovered in between 80% and 100% yield based on V2O5. Red transparent crystals of alpha-Ag3VO4 crystallize in the monoclinic space group C2/c, with cell parameters a = 10.1885(16) A, b = 4.9751(8) A, c = 10.2014(17) A, beta = 115.754(3) degrees .     

氢键构筑的二维网状结构镍配合物[Ni(en)2(dpas)2]的合成、晶体结构及电化学性质

A new 2D Hydrogen-bonded network complex [Ni(en)2(dpas)2] (Nadpas=sodium diphenylamine sulphonic acid salt,en=ethanediamine) has been synthesized in aqueous solution,and characterized by elemental analysis,IR. The crystal structure was determined by single-crystal X-ray diffraction. The complex crystallizes in space group P21/c,with cell parameters a=0.605 6(5)nm,b=1.448 1(5) nm,c=1.711 9(5)nm,β=93.257(5)°,and V=1.498 9(14) nm3,Dc=1.497 g·cm-3,Z=2,F (000)=708,R=0.027 7,wR=0.072 5. The crystal structure shows that the nickel atom is coordinated with four nitrogen atoms from the two en and two oxygen atoms from two dpas to form a mononuclear complex. Furthermore,the adjacent complex units are extended into a 2D supramolecular network through hydrogen bonds.     

Low energy electron diffraction and low energy electron microscopy microspot I/V analysis of the (4 x 4)O structure on Ag(111): surface oxide or reconstruction?

A low energy electron diffraction (LEED) I/V analysis was performed of the (4 x 4) oxygen structure on Ag(111). Two data sets were used, one recorded with a conventional LEED system and a second with a low energy electron microscope (LEEM). The data sets agree well with each other, demonstrating that I/V structure analyses can be performed with the same quality with LEEM as with conventional LEED. The structure obtained confirms the recently proposed model that involves a reconstruction of the Ag(111) surface. Previous models based on a thin layer of Ag(2)O that had been accepted for more than 30 years are disproved. The reconstruction model contains two units of six triangularly arranged Ag atoms and a stacking fault in one half of the unit cell. The six O atoms per unit cell occupy sites in the trenches between the Ag(6) triangles. Small lateral displacements of the Ag atoms lift the mirror symmetry of the structure, leading to two nonequivalent groups of O atoms. The atoms of both groups are located approximately 0.5 Angstrom below the top Ag layer, on fourfold positions with respect to the top layer Ag atoms. Ag-O distances between 2.05 and 2.3 Angstrom are found. The oxygen atoms exhibit large static or dynamic displacements of up to 0.3 Angstrom at 300 K.     

α-Diimines as monodentate or bridging ligands; synthesis and characterization of palladium(II) and rhodium(I) di(t-butyl)diimine complexes

Complexes of di(t-butyl)diimine with PdCl₂(PhCN)₂ and with (CO)₂RhCl dimer have been synthesized and characterized. The diimine ligand is monodentate bonded in PdCl₂(t-butyldiimine)₂, while in (t-butyldiimine)-[Rh(CO)₂Cl]₂ it bridges two Cl(CO)₂Rh units.     

Capacitive properties of low potential electro-polymerized polyfluorene and activated carbon composite electrode

Polyfluorene (PF) film has been successfully electropolymerized at lower potential (0.91 V vs.Ag/AgCl) in the mixed electrolyte of boron trifluoride diethyl etherate and trifluoroacetic acid.The PF film is characterized to have about 10 repeat units and no presence of ketonic defect site.UV-vis and photoluminescent spectral studies indicate that the PF film is blue light emitting.From cyclic voltammetry and galvanostatic charge-discharge tests in 1 M lithium perchlorate/acetonitrile electrolyte,the polyfluorene/activated carbon electrode shows a specific capacitance of 227.1 F g-1 (per active layer mass) and reversible redox reaction at the potential of 1.4 V in a three electrode configuration.An asymmetric electrochemical capacitor based on this composite electrode and activated carbon electrode exhibits a specific energy of 14.7 Wh kg-1 (per active layer mass).These results indicate that electrochemically prepared polyfluorene could be used as energy storage component for electrochemical application.     

Kinetics and mechanism of the chain reaction between <Emphasis Type="Italic">N</Emphasis>-phenyl-1,4-benzoquinone monoimine and thiophenol

The kinetics of the reaction between N-phenyl-1,4-benzoquinone monoimine (quinone monoimine) and thiophenol is studied in chlorobenzene at 343 K. The reaction has the same mechanism proposed earlier for a similar reaction involving N,N'-diphenyl-1,4-benzoquinone diimine (quinone diimine). This mechanism has two paths: chain and nonchain. An important difference between the kinetics of the two reactions is the apparent reversible nature of the chain reaction in the quinone monoimine + thiophenol system. This nature reveals itself when the concentrations of thiophenol are comparable to or slightly higher than the concentrations of quinone imine. In light of this, kinetic research is conducted under conditions where the concentrations of thiophenol are significantly higher than those of quinone monoimine, allowing us to simplify the kinetic features and obtain interpretable data. The rate constants of the reaction’s elementary steps are estimated and found to be three to five times lower for the reaction involving quinone monoamine than for the one involving quinone diimine. Both reactions have relatively short chains whose lengths do not exceed several tens of units.     

Complexation,crystallography, and electrochemistry of new chelating nicotinyl and thiazolyl anthraquinone ligands

Chelating anthraquinone ligands that contain nicotinyl and thiazolyl binding units have been synthesized. The complexation chemistry of these new ligands has also been explored using cadmium(II), lead(II), and ruthenium(II). The nicotinic substituted anthraquinone acts as a bidentate ligand, while the thiazolyl substituted anthraquinone binds in a tetradentate arrangement, not previously observed. Due to steric limitations, the number of these ligands that can coordinate to metal centers appears limited to bis-substituted products. Crystallographic data for both the free ligands and the cadmium and lead complexes are reported. Electrochemical data indicate that interaction does not take place between the intraannular carbonyl group and the neighboring metal centers within these complexes.     

A Two-dimensional Metallic Oxide Constructed from Molybdenum Clusters and Ag(I)-[3-(2-pyridyl)-pyrazole] Cationic Coordination Components

A new polyoxomolybdate compound [Ag3(HL)4](PMol204o)] 1 (HE = 3-(2-pyridyl)pyrazole) has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction,elemental analyses,TG and IR spectroscopy. The compound crystallizes in trielinie,space group P(1) with a = 10.375(3),b = 12.076(3),c= 13.196(4) (A°),α= 84.170(4),β =71.961(3),γ = 86.326(4)°,V = 1563.1(7) (A°)3,C32H28Ag3Mo12N12O40P,Mr= 2726.52,Dc = 2.897g/cm3,μ(MoKα) = 3.366 mm-1,F(000) = 1284,Z = 1,the final R = 0.0587 and wR = 0.1312 for 4139 observed reflections (Ⅰ ＞ 2σ(I)). X-ray diffraction analyses reveal that the PMo12O403- clusters in compound 1 are linked by four Ag3(HL)43+ units via the terminal oxygen atoms to form a two-dimensional architecture. The symmetrical unit of Ag3(HL)43+ exhibits two distinct Ag(Ⅰ)environments:a two-coordinate {AgN2} site and a five-coordinate {AgN3O2} site which links to two molybdate clusters.     

A new oxoanion: [IO]3- containing I(V) with a stereochemically active lone-pair in the silver uranyl iodate tetraoxoiodate(V), Ag4(UO2)4(IO3)2(IO4)2O2

The hydrothermal reaction of elemental Ag, or water-soluble silver sources, with UO3 and I2O5 at 200 degrees C for 5 days yields Ag4(UO2)4(IO3)2(IO4)2O2 in the form of orange fibrous needles. Single-crystal X-ray diffraction studies on this compound reveal a highly complex network structure consisting of three interconnected low-dimensional substructures. The first of these substructures are ribbons of UO8 hexagonal bipyramids that edge-share to form one-dimensional chains. These units further edge-share with pentagonal bipyramidal UO7 units to create ribbons. The edges of the ribbons are partially terminated by tetraoxoiodate(V), [IO4]3-, anions. The uranium oxide ribbons are joined by bridging iodate ligands to yield two-dimensional undulating sheets. These sheets help to form, and are linked together by, one-dimensional chains of edge-sharing AgO7 capped octahedral units and ribbons formed by corner-sharing capped trigonal planar AgO4 polyhedra, AgO6 capped square pyramids, and AgO6 octahedra. The [IO4]3- anions in Ag4(UO2)4(IO3)2)(IO4)2O2 are tetraoxoiodate(V), not metaperiodate, and contain I(V) with a stereochemically active lone-pair. Bond valence sum calculations are consistent with this formulation. Differential scanning calorimetry measurements show distinctly different thermal behavior of Ag4(UO2)4(IO3)2(IO4)2O2 versus other uranyl iodate compounds with endotherms at 479 and 494 degrees C. Density functional theory (DFT) calculations demonstrate that the approximate C2v geometry of the [IO4]3- anion can be attributed to a second-order Jahn-Teller distortion. DFT optimized geometry for the [IO4]3- anion is in good agreement with those measured from single-crystal X-ray diffraction studies on Ag4(UO2)4(IO3)2(IO4)2O2.     

Biologically compatible, phosphorescent dimetallic rhenium complexes linked through functionalized alkyl chains: syntheses, spectroscopic properties, and applications in imaging microscopy

A range of luminescent, dimetallic complexes based upon the rhenium fac-tricarbonyl diimine core, linked by aliphatic chains of varying lengths and functionality, have been synthesized and their photophysical properties examined. Each complex displays characteristic (3)M(Re)L(diimine)CT emission in aerated acetonitrile solution, with long lifetimes in the range of 129-248 ns and corresponding quantum yields in the range 3.2-8.0%. In aqueous solution, as opposed to acetonitrile, the complexes generally show a small hypsochromic shift in λ(em) and an extension of the (3)MLCT lifetime, attributed to a hydrophobically driven association of the alkyl chains with the rhenium-bound diimine units. In live cell imaging experiments using MCF7 cells the complexes all show good uptake by non-energy dependent mechanisms without endosomal entrainment, and with varying propensity to localize in organelles. The degrees of uptake and localization properties are discussed in terms of the length and chemical nature of the linkers, and in terms of the likely interactions between these and the various cellular components encountered.     

树枝状纳米银颗粒的制备与电活性

在Ag(NH3)2+溶液中,在钛基体上电沉积出树枝状纳米银颗粒,研究了沉积电位对树枝状纳米银颗粒形成的影响,探讨了这种树枝状纳米银颗粒形成的机理,并研究了这种钛基树枝状纳米银电极(Ag/Ti)在碱性溶液中对甲醛氧化的电催化活性。结果表明,在30 mmol/LAg(NH3)2+以及沉积电位在-1.8～-1.2 V(vsAg)时,形成了形态为树枝状的纳米银颗粒。在沉积电位为-1.6 V(vs Ag),Ag(NH3)2+浓度为30 mmol/L的溶液中,电沉积制备的这种树枝状纳米银电极(Ag/Ti)对甲醛氧化具有强的电催化活性。循环伏安曲线表明,在0.1 mol/LNaOH溶液中以及甲醛的浓度范围在0～40 mmol/L,甲醛浓度和它的氧化峰电流密度呈现良好的线性关系,检测下限达到0.662 mmol/L,这种新型的树枝状纳米银电极有望作为甲醛检测的传感器。     

Chlorpromazine hydrochloride as a new redox indicator in vanadametry

Chlorpromazine hydrochloride is proposed as an indicator in the vanadametric titration of iron(II) and molybdenum(V). It gives a sharp, reversible colour change from green to violet at the equivalence point. It has advantages over the diphenylamine class of indicators. Its redox and transition potentials are reported.