Quasi-reversible One-electron Research Articles

DNA Binding Test, X-Ray Crystal Structure, Spectral Studies, TG-DTA, and Electrochemistry of [CoX 2 (dmdphphen)] (Dmdphphen Is 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline, X = Cl, and NCS) Complexes.

Two new neutral mixed-ligand cobalt(II) complexes, [CoCl2(dmdphphen)] 1 and [Co(NCS)2(dmdphphen)] 2, where dmdphphen is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, were synthesized and characterized by an elemental analysis, UV-Vis, IR, TG/DTA, cyclic voltammetry CV, and single X-ray diffraction. Complex 2 crystallized as monoclinic with a space group P21/c. Co(II) ions are located in a distorted tetrahedral environment. TG/DTA result shows that these complexes are very stable and decomposed through one-step reaction. The two complexes exhibit a quasireversible one-electron response at −550 and 580 mV versus Cp2Fe/Cp2Fe+, which has been assigned to Co(I)/Co(II) and Co(II)/Co(III) couples. Absorption spectral studies reveal that such complexes exhibit hypochromicity during their interaction with CT-DNA.

Studies of Iron(III) Porphyrinates Containing Silanethiolate Ligands

The chemistry of several iron(III) porphyrinates containing silanethiolate ligands is described. The complexes are prepared by protonolysis reactions of silanethiols with the iron(III) precursors, [Fe(OMe)(TPP)] and [Fe(OH)(H2O)(TMP)] (TPP = dianion of meso-tetraphenylporphine; TMP = dianion of meso-tetramesitylporphine). Each of the compounds has been fully characterized in solution and the solid state. The stability of the silanethiolate complexes versus other iron(III) porphyrinate complexes containing sulfur-based ligands allows for an examination of their reactivity with several biologically relevant small molecules including H2S, NO, and 1-methylimidazole. Electrochemically, the silanethiolate complexes display a quasi-reversible one-electron oxidation event at potentials higher than that observed for an analogous arenethiolate complex. The behavior of these complexes versus other sulfur-ligated iron(III) porphyrinates is discussed.

Insights into the electrochemical behaviour of composite materials: Monovacant polyoxometalates @ porous metal-organic framework

The first electrochemical investigation of composites materials based in polyoxometalates (POMs) encapsulated in the porous Metal-Organic Framework (MOF) MIL-101 is reported. The electrochemical behaviour of the porous MIL-101 and composite materials based in two monovacant Keggin-type POMs {K7[PW11O39]·10H2O (PW11) and K8[SiW11O39]·13H2O (SiW11)} encapsulated in MIL-101 (respectively, PW11@MIL-101 and SiW11@MIL-101) were studied by cyclic voltammetry. Initially, to investigate the influence of the support MIL-101 in the electrochemical behaviour of the two monovacant POMs, the compounds were individually immobilized on the surface of a pyrolytic graphite (PG) electrode. A reversible surface-controlled redox signal attributed to the chromium metal centres (Cr3+/Cr2+) was identified in MIL-101, and this represents the first electrochemical study of this MOF material. The monovacant compounds PW11 and SiW11 also revealed surface-controlled processes corresponding to WVI↔WV reductions. PW11 showed two reversible signals (involving one or two electrons), whereas SiW11 showed a quasi-reversible one-electron and a reversible two-electron process for the first and second W reductions, respectively. For the latter, an extra process was detected and attributed to the formation of β-isomer (β-SiW11). When the composites materials PW11@MIL-101 and SiW11@MIL-101 were immobilized on the surface of the electrode, the support MIL-101 maintained its characteristic electrochemistry and the redox potentials of the POMs were not significantly changed. However, when encapsulated inside the cages of the support material the POMs revealed a distinct electrochemical behaviour, given that their redox processes became diffusion-controlled, indicating that the POMs have some degree of mobility inside the support framework.

Chemistry of mixed-ligand complexes with variable valence VOz+ (z = 2, 3) incorporating pentadentate hydrazone ligands

2-Hydroxybenzoylhydrazide reacts with an equimolar amount of [VIVO(acac)2] and [VIVO(bzac)2] [where acac− and bzac− are the monoanionic forms of acetylacetone (Hacac) and benzoylacetone (Hbzac) respectively] in the presence of an equimolar amount of 2,2′-bipyridine (bipy) in methanol to afford the tetravalent complexes [VIVO(HL1)(bipy)] (1) and [VIVO(HL2)(bipy)] (2) respectively [where (HL1)2− and (HL2)2− represent the dianionic forms of the 2-hydroxybenzoylhydrazone of acetylacetone (H3L1) and benzoylacetone (H3L2) respectively]. On replacing bipy by 8-hydroxyquinoline (Hhq) or vanillin (Hvan), the pentavalent complexes [VVO(HL1/HL2)(hq)] (3/4) and [VVO(HL1/HL2)(van)] (5/6) respectively were obtained. These pentadentate hydrazone ligands bind the vanadium in a tridentate dinegative meridional fashion utilizing their enolic-O, one imine-N and amide-O (in the enol form), leaving the other two potential donor sites, viz., phenolic-O and the other imine-N, which are practically H-bonded intramolecularly, as is evident from IR, 1H NMR and X-ray diffraction (of 3 and 4) studies. The EPR active tetravalent complexes 1 and 2 exhibit a quasi-reversible one-electron oxidation peak near +0.90V, while the pentavalent complexes 3 and 4 exhibit quasi-reversible one-electron reduction peaks near −0.07V versus SCE in CH2Cl2 solution. The [VVO(HL)(van)] complexes 5 and 6 display two quasi-reversible one-electron reduction peaks near +0.06V and near +0.40V versus SCE in CH2Cl2 solution, attributed to the successive reduction of VV→VIV and VIV→VIII respectively.

Redox Routes to Substitution of Aluminum(III): Synthesis and Characterization of (IP–)2AlX (IP = α-iminopyridine, X = Cl, Me, SMe, S2CNMe2, C≡CPh, N3, SPh, NHPh)

Redox active ligands are shown to facilitate a variety of group transfer reactions at redox inert aluminum(III). Disulfides can be used as a two-electron group transfer reagent, and we show that (IP(-))(2)AlSR can be formed by reaction of [(THF)(6)Na][(IP(2-))(2)Al] (1c) with disulfides RSSR (where X = C(S)NMe(2), 4; SMe, 5). In a more general redox route to substitution of aluminum bis(iminopyridine) complexes, we report zinc(II) salts as a group transfer reagent. Reaction of [((R)IP(2-))(2)Al](-) (R = H, 1c; Me, 1d) with ZnX(2) affords ((R)IP(-))(2)AlX (where IP = iminopyridine, R = H, and X = Cl, 2; CCPh, 6; N(3), 7; SPh, 8; or R = Me and X = NHPh, 9). Single crystal X-ray diffraction analysis of the complexes reveal that each of the five coordinate complexes reported here has a trigonal bipyramidal geometry with τ = 0.668 - 0.858. We observed a correlation between the greatest deviations from ideal trigonal bipyramidal symmetry (lowest τ values), the bond lengths consistent with smallest degree of ligand reduction, and the least polarizable X ligand in (IP(-))(2)AlX. Complex 4 is six-coordinate and is best described as distorted octahedral. Variable temperature magnetic susceptibility measurements indicate that each of the complexes 3-9 has a biradical electronic structure similar to previously reported 2. Magnetic exchange coupling constants in the range J = -94 to -212 cm(-1) were fit to the data for 2-9 to describe the energy of antiferromagnetic interaction between ligand radicals assuming a spin Hamiltonian of the form Ĥ = -2JŜ(L(1))·Ŝ(L(2)). The strongest coupling occurs when the angle between the ligand planes is smallest, presumably to afford good overlap with the Al-X σ* orbital. Electrochemical properties of the complexes were probed using cyclic voltammetry and each of 3-9 displayed a reversible two-electron reduction and two quasi-reversible one-electron oxidation processes. The energy of the ligand based redox processes for 2-9 differ by about 150 mV over all complexes and show a correlation with the degree of IP(-) reduction observed crystallographically; more reduced IP(-) ligands require higher potentials for further reduction. Comproportionation constants that describe the equilibrium for the reaction (IP(-))(2)AlX + (IP)(2)AlX ↔ (IP(-))(IP)AlX fall in the range of K(c) = 10(5.7) to 10(7.9) for 3-9.

Synthesis and spectral characterization of ternary mixed-vanadyl β-diketonate complexes with Schiff bases

A new method to synthesize some mononuclear ternary oxovanadium(IV) complexes of the general formula [VO(β-dike)(SB)] (where Hβ-dike=acetylacetone; benzoylacetone or dibenzoylmethane, HSB=Schiff bases) has been explored by stepwise substitutions of acetylacetonate ion of VO(acac)2 with Schiff bases. The substituted acetylacetone could be fractionated out with p-xylene as an azeotrope. The complexes were characterized by elemental analyses, molecular weight determinations, spectral (electronic, infrared, 1H NMR, EPR and powder XRD) studies, magnetic susceptibility measurements and cyclic voltammetry. Molar conductance measurements indicated the complexes to be non-electrolytes in nitrobenzene. Bidentate chelating nature of β-diketones and Schiff base anions in the complexes was established by infrared and NMR spectra. Molecular weight determinations confirmed mononuclear nature of the complexes. The EPR spectra illustrated coupling of the unpaired electron with 51V nucleus (I=7/2). Cyclic voltammograms of all the complexes displayed two-step oxidation processes. The oxidation peak potential corresponded to the quasireversible one-electron oxidation process of the metal center, yielding V(V) species. Transmission electron microscopy (TEM) indicated spherical particles of ∼200nm diameter. The synthesized complexes are mixed-ligand complexes showing a considerable hydrolytic stability in which vanadium is having coordination number 5. A square pyramidal geometry around vanadium has been assigned in all the complexes.

Nano-sized, ternary oxovanadium(IV) complexes containing electron-rich oxygen-based ligands

Some mononuclear mixed-carboxylato β-diketonato oxovanadium(IV) complexes of the general formula [VO(β-dike)(RCOO)] (where Hβ-dike = acetylacetone; benzoylacetone or dibenzoylmethane, R = C15H31 or C17H35) have been synthesized from VO(acac)2 by stepwise substitutions of acetylacetonate ion with straight chain fatty acids (RCOOH) and β-diketones in p-xylene under reflux. The substituted acetylacetone could be fractionated out with p-xylene as an azeotrope. These were characterized by elemental analyses, molecular weight determinations, spectral (electronic, infrared, 1H NMR, EPR and powder XRD) studies, magnetic susceptibility measurements and cyclic voltammetry. Molar conductance values indicated the complexes to be non-electrolytes in nitrobenzene. Bidentate chelating nature of β-diketonate and carboxylate ligands in the complexes was established by infrared and NMR spectra. Molecular weight determinations confirmed mononuclear nature of the complexes. The EPR spectra illustrated coupling of the unpaired electron with 51V nucleus (I = 7/2). Cyclic voltammograms of all the complexes displayed one-step oxidation processes. The oxidation peak potential corresponded to the quasireversible one-electron oxidation process of the metal center, yielding V(V) species. Powder XRD and transmission electron microscopy (TEM) studies indicated the particles of these were lying in the nano-size range. The synthesized complexes are a new type of mixed-ligand complexes in which vanadium is having coordination number 5. A square pyramidal geometry around vanadium has been assigned in all the complexes.

Liquid-crystalline oxovanadium(IV) complexes accessed from bidentate [N, O] donor salicylaldimine Schiff-base ligands

A series of bis[4-(n-alkoxy)-N-(4′-R-phenyl)salicylideneiminato]oxovanadium(IV) complexes (n = 6, 10, 14, 16, 18 and R = C3H7) were prepared and their mesogenic properties were investigated. The mesomorphic behaviors of the compounds were studied by polarized optical microscopy and differential scanning calorimetry. Ligands display SmA/SmC and unexpected nematic mesophases. The complexes bearing longer alkoxy carbon chain (n = 10, 14, 16, and 18) showed both monotropic or enantiotropic transitions with smectic A and high ordered smectic E phases. However, the complex with shorter carbon chain length (n = 6) showed monotropic transition with an unprecedented nematic (N) phase. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimized structure. A square-pyramidal geometry for the vanadyl complexes has been suggested. A νV=O stretching value of ∼970 cm−1 corroborated absence of any V = O ··· V = O interactions. Cyclic voltammetry revealed a quasireversible one-electron response at 0.61 V for the VO(IV)–VO(V) redox couple. Variable temperature magnetic susceptibility measurements of the vanadyl complexes suggested absence of any exchange interactions among the vanadyl spin centers.

Synthesis, Spectroscopic Characterization, and In Vitro Antimicrobial Screening of 16-Membered Tetraazamacrocyclic Schiff-Base Ligand and its Complexes with Co(II), Ni(II), Cu(II), and Zn(II) Ions

A 16-membered tetraazamacrocyclic ligand has been synthesized by condensation reaction of 2-methyl acetoacetanilide with 1,8-diaminonaphthalene, and the metal complexes of the type [MLCl2] [M = Co(II), Ni(II), Cu(II), Zn(II)] were prepared by interaction of the ligand with metal salts. The ligand and its complexes were characterized by various spectroscopic studies. The mode of bonding and the overall geometry of these complexes have been deduced by elemental analysis, molar conductance values, Fourier-transform infrared (FT-IR), 1H-nuclear magnetic resonance (NMR), fast-atom bombardment (FAB) mass, electron paramagnetic resonance (EPR), and ultraviolet–visible (UV-VIS) spectroscopy along with magnetic measurement studies. An octahedral geometry has been envisaged for all these complexes, while a distorted octahedral geometry has been noticed for the Cu(II) complex. The cyclic voltammograme of the Cu(II) complex exhibits a quasi-reversible one-electron transfer wave for the Cu(II)/Cu(I) couple. The low conductivity data of all the complexes suggest their nonionic nature. These complexes have also been screened against pathogenic bacteria and fungi in vitro as growth-inhibiting agents.

5-Nitro-1,10-phenanthroline bis(N,N-dimethylformamide-Κ′O)-bis(perchlorato) copper(II): synthesis, structural characterization, and DNA-binding study

The hexa-coordinated copper(II) complex [Cu(L)(DMF)2(ClO4)2], where L = 5-nitro-1,10-phenanthroline, was synthesized and characterized. The X-ray crystal structure shows that the copper is coordinated by the two N-atoms of the 1,10-phenanthroline ligand plus four O-atoms, two from DMF ligands and two from the perchlorate anions. Thermal analysis showed that the complex was stable up to 285 °C. The interaction of the complex with calf thymus DNA was investigated using absorption and emission spectroscopic studies, and the binding constant (K b) and linear Stern–Volmer quenching constant (K sv) have been determined. Electrochemical characterization of the complex in acetonitrile showed a quasi-reversible one-electron exchange voltammogram for the Cu2+/Cu+ redox couple at ca. E 1/2 = −1.00 V (versus SCE) with ΔE = 200 mV and i pc/i pa ≈ 1.

Synthesis, characterisation and mesomorphic properties of a homologous series of oxovanadium(iv) complexes containing a bidentate [N,O] donor Schiff base mesogen

A series of oxovanadium(iv) complexes of the type [VO(L)2], [L = N-(4-n-alkoxysalicylaldimine)-4-hexadecyloxyaniline, n = 8, 10, 12, 14, 16 or 18] have been synthesised and characterised by FT–IR, 1H NMR, 13CNMR, UV–Vis, and FAB mass and magnetic susceptibility measurements. The ligands are coordinated to the vanadyl ion in a bidentate fashion. The mesomorphic behaviour of the ligands and their vanadyl complexes was investigated by polarising optical microscopy and differential scanning calorimetry. The compounds were all highly thermally stable, and their mesomorphic properties were found to depend on the length of the carbon chain. Both the ligands and their higher homologue complexes exhibited a SmC mesophase. In the case of the lower homologues the ligands exhibited the SmC phase but their complexes a SmA mesophase. The mesophase–isotropic transition temperatures for the complexes were significantly higher than those of the ligands. Variable temperature magnetic susceptibility measurements on the vanadyl complexes clearly suggested absence of any exchange interactions among the vanadyl spin centres. Cyclic voltammetry showed a quasi-reversible one-electron response at 0.51 V for the VO(iv)–VO(v) redox couple. Density functional theory studies carried out using DMol3 at the BLYP/DNP level to determine the energy-optimised structure revealed a distorted square pyramidal geometry for the vanadyl complexes, with the alkoxy tails projecting away from one another.

Lamellar columnar mesomorphism in a series of oxovanadium(IV) complexes derived from N, N/-di-(4-n-alkoxysalicylidene)diaminobenzene

Abstract A series of new nondiscoid shaped square pyramidal oxovanadium(IV)-Schiff base complexes containing 4-substituted alkoxy chains on the aromatic rings, [VO(4-C n H 2n + 1 O) 2 salophen)] {n = 14, 16, 18; salophen = N, N/-phenylnebis(salicylideneiminato)} have been prepared and their mesogenic properties investigated. The ligands and the complexes were characterized by FT-IR, CHN, 1 H-NMR, UV–vis and FAB mass spectrometry. Presence of V═O stretching mode at ~ 980 cm − 1 indicated absence of any intermolecular … V═O ..... V═O … interactions with no dependence on the chain length. Variable temperature magnetic susceptibility measurements of the complexes also suggested lack of such exchange interaction. Cyclic voltammetry showed a quasireversible one-electron response at 0.75 V for the VO(IV)–VO(V) redox couple. DSC coupled with polarized optical microscopy showed the ligands to be nonmesogenic but the complexes exhibited an unprecedented thermally stable columnar mesophase in the 136–154 °C. X-ray diffraction technique, confirmed that the structure of the mesophase is lamellar columnar in type (Col l ). DFT studies using DMol3 were carried out to obtain the optimized geometry of the complex.

Phenolate and phenoxyl radical complexes of Cu(ii) and Co(iii), bearing a new redox active N,O-phenol-pyrazole ligand

The synthesis and characterisation of the new N,O-phenol-pyrazole pro-ligand, (pz)LH, comprising a pyrazole covalently linked to an o,p-di-tert-butyl-substituted phenol, are herein reported. In CH(2)Cl(2) at room temperature, the cyclic voltammogram (CV) of (pz)LH exhibits a quasi-reversible one-electron oxidation process (at E(1/2) = 0.66 V vs. Fc(+)/Fc) attributed to the formation of the phenoxyl radical cation [(pz)LH]˙(+). (pz)LH reacts with M(II)(BF(4))(2) (M = Cu, Co) in a 2:1 ratio to afford the bis-Cu(pz)L(2) (1) and tris-Co(pz)L(3) (2) complexes respectively. The X-ray structure of 1 reveals a Cu(II) ion in a square-planar trans-Cu(II)-N(2)O(2) coordination environment whereas that of 2 consists of a Co(III) ion with an octahedral mer-N(3)O(3) coordination sphere; formed by the chelation of two (in 1) or three (in 2) N,O-bidentate phenolate ligands respectively. Both structures are preserved in CH(2)Cl(2) solution, as revealed by their NMR (for 2) and EPR (for 1) data. The CVs of 1 and 2 consist of two (at E(1/2): 0.43 and 0.58 V vs. Fc(+)/Fc) and three (E(1/2) = 0.12, 0.54 and 0.89 V vs. Fc(+)/Fc) reversible one-electron oxidation processes, respectively. The one-electron electrochemical oxidation of 1 and 2 produces the oxidised species, 1(+) and 2(+), which are stable for several hours at room temperature under inert atmosphere in CH(2)Cl(2). The UV/vis and EPR data obtained for 1(+) and 2(+) are unambiguously consistent with the latter being formulated as Cu(II)- and Co(III)-phenoxyl radical complexes, as [Cu(II)((pz)L˙)((pz)L)](+) and [Co(III)((pz)L˙)((pz)L)(2)](+) respectively.

Two macrocyclic pentaaza compounds containing pyridine evaluated as novel chelating agents in copper(II) and nickel(II) overload

Two pentaaza macrocycles containing pyridine in the backbone, namely 3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),14,16-triene ([15]pyN 5), and 3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),15,17-triene ([16]pyN 5), were synthesized in good yields. The acid–base behaviour of these compounds was studied by potentiometry at 298.2 K in aqueous solution and ionic strength 0.10 M in KNO 3. The protonation sequence of [15]pyN 5 was investigated by 1H NMR titration that also allowed the determination of protonation constants in D 2O. Binding studies of the two ligands with Ca 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, and Pb 2+ metal ions were performed under the same experimental conditions. The results showed that all the complexes formed with the 15-membered ligand, particularly those of Cu 2+ and especially Ni 2+, are thermodynamically more stable than with the larger macrocycle. Cyclic voltammetric data showed that the copper(II) complexes of the two macrocycles exhibited analogous behaviour, with a single quasi-reversible one-electron transfer reduction process assigned to the Cu(II)/Cu(I) couple. The UV–visible-near IR spectroscopic and magnetic moment data of the nickel(II) complexes in solution indicated a tetragonal distorted coordination geometry for the metal centre. X-band EPR spectra of the copper(II) complexes are consistent with distorted square pyramidal geometries. The crystal structure of [Cu([15]pyN 5)] 2+ determined by X-ray diffraction showed the copper(II) centre coordinated to all five macrocyclic nitrogen donors in a distorted square pyramidal environment.

ChemInform Abstract: Substituent Effects in Dinuclear Paddlewheel Compounds: Electrochemical and Spectroscopic Investigations

Abstract This review summarizes substituent effects in dinuclear compounds supported by diarylformamidinate (form) ligands, where aryl is phenyl substituted with various polar groups (X). These dinuclear compounds, M2(form)4(Lax)m with M as Mo, Ru, Rh, or Ni, Lax as either neutral or anionic axial ligand, and m=0–2, may undergo up to three (quasi)reversible one-electron, metal-centered redox processes. Linear correlations have been established between the electrode potentials (E1/2, Epc or Epa) and the substituent constants (σ) according to the following Hammett equation: ΔE=E(X)−E(H)=ρ(Σ σ), with the reaction constant ρ ranging from +60 to +100 mV. The existence of such relationships indicates that the energy levels of the frontier orbitals of dinuclear species are controlled precisely by the substituent within each series, and generally decrease with an increase in the electron withdrawing ability of the substituent. However, nearly identical UV–vis absorption spectra were observed within each homologous series, and one can infer a minimal substituent perturbation on the distribution of upper valence molecular orbitals. Axial ligation of organic π acids such as CO and phenylacetylide in both the diruthenium and dirhodium series also provides insight to the activation of these substrates by the dinuclear core, and the linear free energy relationship therein. A brief overview of other investigations of substituent effects in dinuclear compounds is provided also.

Synthesis, characterization and coordinating properties of an NNS donor system, 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone (HMPzPyr), and it's cobalt(III), nickel(II) and copper(II) complexes

The ligational behaviour of 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone has been demonstrated by isolation and characterisation of its complexes with cobalt(III), nickel(II) and copper(II) with different counterions. Magnetic and spectral features indicate [Co(MPzPyr) 2 ]X (X = Cl, Br, NO 3 , ClO 4 or BF 4 ) as the diamagnetic octahedral species with the ligand in the deprotonated thiol form, while [Ni(HMPzPyr) 2 ]X 2 (X = Cl, Br or NO 3 ) is proposed as octahedral complex with the ligand in the neutral thione form. However, at pH ∼6, nickel(II) salts afford octahedral bis-nickel(II) complex, Ni(MPzPyr) 2 , while copper(II) salts in acetonitrile medium give Cu(MPzPyr)X (X = Cl, Br or NO 3 ) with the deprotonated ligand. IR spectra indicate that the pyrazolyl ring nitrogen ( 2 N), the azomethine nitrogen and the sulphur atom are the points of attachment with the metal ion in all these complex species. The cyclovoltammetric study of copper(II) complexes reveals the quasi-reversible one-electron process (Cu II → Cu I ), where the EPR data confirm the presence of d x2―y2 ground state of these complexes.

Synthesis and characterization of stable thiazolylazo anion radical complexes of ruthenium(II)

Two stable thiazolylazo anion radical complexes of ruthenium(II), [Ru(L1•−)(Cl)(CO)(PPh3)2] (1) and [Ru(L2•−)(Cl)(CO)(PPh3)2] (2) (where L1 = 2′-Thiazolylazo-2-imidazole and L2 = 4-(2′-Thiazolylazo)-1-n-hexadecyloxy-naphthalene), have been synthesized and characterized by spectroscopic and electrochemical techniques. The radical nature of the complexes has been confirmed from their room temperature magnetic moments and X-band ESR spectra. The radical complexes display a moderately intense (e ~ 104 M−1 cm−1) and relatively broad band in 430–460 nm region. In the microcrystalline state, complexes (1) and (2) display strong ESR signals at g = 1.951 and g = 1.988, respectively. In CH2Cl2 solution, complexes (1) and (2) show a quasireversible one-electron response near −0.64 and −0.59 V, respectively, versus Ag/AgCl due to the radical redox couple [RuII(L)(Cl)(CO)(PPh3)2]/[RuII (L•−)(Cl)(CO)(PPh3)2].

Formation of N-(1-ferrocenoylpyrrolidine-2-carbonyl)-N,N′-dicyclohexylurea: Dead-end in the preparation of ferrocene-modified peptides

This paper reports the synthesis, characterisation and electrochemical properties of Fc-Pro-DCU 3. The activation of Fc-Pro-OH with DCC in the absence of racemization reducing agent results in the formation of N-(1-ferrocenoylpyrrolidine-2-carbonyl)-N,N′-dicyclohexylurea, as result of O/N-acyl shift in the acylisourea intermediate. Compound 3 exhibits quasi-reversible one-electron oxidation of ferrocenoyl moiety at E 1/2 = 0.62 V.

A Novel Tantalum Cluster Chalcohalide Ta4S1.5Se7.5I8

Single crystals of Ta4S1.5Se7.5I8 are obtained by heating Ta, S, Se and I2 at 300 °C in 4.0:1.0:8.0:4.4 molar ratio. The structure was determined by X-ray analysis and consists of molecular clusters [Ta4(μ4-S)(μ2-QaxSeeq)4I8] (Q ≈ Se0.87S0.13). The tantalum atoms form a square with long Ta…Ta distances (3.26–3.32 Å), with four dichalcogenide ligands bridging the Ta–Ta edges and a sulfur atom capping the square. Each Ta atom has two terminal iodine atoms. Raman spectroscopy study shows the presence of the characteristic absorption band at 396 cm−1 which is due to the Ta4–μ4-S vibrations. Cyclic voltammetry shows that Ta4S1.5Se7.5I8 in solid state undergoes quasi-reversible one-electron oxidation which is metal-centered.

Cyclic voltammetric investigations of copper(II) complexes with various imidazoles in dimethylformamide

The cyclic voltammetric behaviour of copper(n) complexes with various imidazoles, viz. imidazole (ImH), 2-methylimidazole (2-Melm), 1,2-dimethylimidazole (1,2-Me 2 Im) and benzimidazole (BzIm) has been investigated in dimethylformamide (DMF) containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) as a supporting electrolyte at a glassy carbon electrode (GCE). All these copper(II) complexes revealed a diffusion-controlled quasi-reversible one-electron transfer process (Cu 2+/+ ). It has been observed that the reduction peak potential becomes less positive (difficult reduction) with increasing concentration of a given ligand. The observed reduction potentials of these complexes become more positive in the order : Im → 2-MeIm → 1,2-Me 2 Im → BzIm. The deviation of reduction potentials from the expected trend based on pK a values of the ligands is attributed to the dominance of steric effects over the electronic effects (i.e. inductive effects) in the case of 2-MeIm and 1,2-Me 2 Im ligands.