Dissociable Proton Research Articles

A group of diphosphine-thiosemicarbazone complexes of palladium: Efficient precursors for catalytic C[sbnd]C and C[sbnd]N coupling reactions

Reaction of 4-R-benzaldehyde thiosemicarbazone (denoted in general as HL-R; where H stands for the dissociable acidic proton and R (R = OCH3, CH3, H, Cl and NO2) for the substituent) with [Pd(dppe)(EtOH)2]2+, generated in situ via interaction of [Pd(dppe)Cl2] (dppe = 1,2-bis(diphenylphosphino)ethane) with AgNO3 in hot ethanol, in the presence of triethylamine affords a group of orange complexes of the type [Pd(dppe)(L-R)]NO3. Structures of [Pd(dppe)Cl2] and [Pd(dppe)(L-OCH3)]NO3 have been determined by X-ray crystallography. In the [Pd(dppe)(L-R)]NO3 complexes, the thiosemicarbazone ligands are coordinated to the metal center as monoanionic bidentate N,S-donors forming five-membered chelate rings. The [Pd(dppe)(L-R)]NO3 complexes show intense absorptions in the visible and ultraviolet regions, which have been analyzed by TDDFT calculations. All the [Pd(dppe)(L-R)]NO3 complexes are found to efficiently catalyze Suzuki-type CC and Buchwald-type CN coupling reactions.

Ternary pentagonal-bipyramidal oxovanadium(V) complexes containing five- and six-membered chelate rings: Syntheses, structures and properties

Reactions of bis(acetylacetonato)oxovanadium(IV) [VO(acac)2] with isolated or in-situ generated α-diketone bis(para-R-benzoylhydrazones) (H2Ln (n = 1–6), where 2H represent the two dissociable amide protons) in methanol or chloroform–methanol (1:3) mixture afford six novel oxovanadium(V) complexes of formula [VO(acac)(Ln)] (1–6) in 51–64% yields. All the complexes have been characterized by elemental analysis, mass spectrometric, solution electrical conductivity, various spectroscopic (IR, UV–Vis, and 1H NMR) and cyclic voltammetric measurements. The complexes are brown in color. They are diamagnetic and non-electrolytes. Molecular structures of all six complexes have been determined by single crystal X-ray crystallography. The metal center in each complex is in a distorted pentagonal-bipyramidal N2O5 coordination sphere. The fused 5,5,5-membered chelate rings forming ON2O-donor (Ln)2− and one of the acetylacetonate-O form a N2O3 pentagonal plane around the vanadium atom, while the second acetylacetonate-O and the oxo atom occupy the two axial positions. In the crystal lattice, the complexes form one-dimensional chain-, ladder- and ribbon-like supramolecular structures via various types of intermolecular non-covalent interactions such as trifurcated OH∙∙∙(O,O,O), bifurcated CH∙∙∙O∙∙∙HC and CH∙∙∙(O,O), simple CH∙∙∙O, π−π, CH∙∙∙π and O∙∙∙O interactions. The spectroscopic features of 1–6 are consistent with their molecular structures. All the complexes are redox active and display a quasi-reversible to irreversible vanadium(V) to vanadium(IV) reduction in the potential range −0.80 to −0.92 V (vs. Ag/AgCl).

Complexation of Uranium(VI) with N-(2-Hydroxyethyl)ethylenediamine- N, N', N'-triacetic Acid in Aqueous Solution: Thermodynamic Studies and Coordination Analyses.

N-(2-Hydroxyethyl)ethylenediamine- N, N', N'-triacetic acid (HEDTA, denoted as H3L in this work, and the three dissociable protons represent those of the three carboxylic groups) is a strong chelating ligand and plays an important role in the treatment and disposal of nuclear wastes as well as separation sciences of f-elements. In this work, the complexation of HEDTA with U(VI) was studied thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were used to measure the complexation constants (298-343 K) and enthalpies (298 K), respectively, at I = 1.0 mol·L-1 NaClO4. Thermodynamic studies identified three 1:1 U(VI)/HEDTA complexes with different degrees of deprotonation, namely, UO2(HL)(aq), UO2L-, and UO2(H-1L)2-, where H-1 represents the deprotonation of the hydroxyl group. The results indicated that all three complexation reactions are endothermic and driven by entropy only. Coordination modes of the three complexes were investigated by NMR and extended X-ray absorption fine structure spectroscopies. In the UO2(HL)(aq) complex, HEDTA holds a tridentate mode, and the coordination occurs to the end of the ethylenediamine backbone. Two oxygens of the two carboxylic groups and one nitrogen of the amine group participate in the coordination. In both UO2L- and UO2(H-1L)2-, HEDTA holds a tetradentate mode and coordinates to U(VI) along the side of the ethylenediamine backbone. The difference is that in the UO2(H-1L)2- complex, the alkoxide form of the HEDTA hydroxyl group directly binds to the U(VI) atom, forming a highly strong chelation.

Proton transfer in nonpolar solvents: an approach to generate electrolytes in aprotic media

Stabilizing charged species in nonpolar solvents is challenging due to their low dielectric constant. As a contrast to formally ionic electrolytes, two series of acidic "potential" electrolytes have been developed in this study. These can be ionized by combining them stoichiometrically with a small molecule base in a typical nonpolar solvent, n-dodecane. The electrolytic conductivity of solutions of bis(2-ethylhexyl)phosphoric acid as mixtures with linear and branched dioctylamines and trioctylamines was measured, and the solutions were found to become increasingly conductive as the concentration increased, demonstrating that proton transfer occurred between the two species. Linear octylamines were found to be most effective at deprotonation. An acid-tipped poly(lauryl methacrylate) polymer (PLMA48-COOH) was also studied to give a polymer soluble in n-dodecane with a single ionizable group located precisely at the end of the polymer chain. Trioctylamine could successfully deprotonate this acid group. Even in an aprotic solvent, the transfer of protons between acidic and basic moieties is a useful method for controlling the properties of dissolved molecules.

Unexpected solvation-stabilisation of ions in a protic ionic liquid: insights disclosed by a bond energetic study.

Equilibrium acidities (pKas) of 42 organic acids were precisely determined in protic ionic liquid (PIL) [DBUH][OTf]. Surprisingly, the often seen homoassociation complication during the pKa measurement of O-H acids in DMSO was not detected in [DBUH][OTf], implying that the incipient oxanion should be better solvation-stabilized by the PIL, although its "apparent" dielectric constant is much lower than that of the conventional molecular solvent DMSO. Evidence showing that the solute ions in the PIL are also free from other specific ion associations like ion-pairing is further demonstrated by the identical pKas of protic amine salts bearing largely different counter-anions. Correlations between the RO-H, N-H, N+-H and RCOO-H bond acidities in [DBUH][OTf] and in water revealed different slopes and intercepts for each individual series, suggesting far superior properties of the DBUH+-based PIL for differentiating the solvation effect of various species in structural analysis to the well applied EAN that is known for leveling out differential solvation.

Design and syntheses of a new family of palladium complexes derived from tridentate ligands and their application as catalysts for Suzuki-Miyaura cross-coupling reactions

Palladium complexes [Pd(L1−5)(PPh3)]ClO4 (LnH (n = 1–5, H = phenolic dissociable proton) (1–5)) were synthesised and characterised by different spectroscopic methods like 1H NMR, IR and UV-visible spectral studies. The molecular structure of the representative complex [Pd(L2)(PPh3)]ClO4 (2) was determined by X-ray crystallography. These new complexes were utilised to study Suzuki-Miyaura cross-coupling reactions. Substituted aryl halides were reacted with the phenylboronic acid in presence of these palladium-based catalysts and sodium hydroxide. Biphenyl and its derivatives were synthesised via. C-C bond formation. The plausible mechanism of these cross-coupling reactions was proposed on the basis of theoretical calculation utilising density functional theory (DFT).

Concomitant polymorphism of an octahedral, homoleptic zinc(II) bis complex of an N,N,O donor hydrazone

Using the 1:1 condensate of benzil and 2-hydrazinopyridine as the ligand HL (H: a dissociable proton), a new zinc(II) complex ZnL2 is synthesized. It is obtained as a mixture of three types of deep red crystals – diamond shaped (1a), rectangular (1b) and pointed tetragonal (1c) which can be separated manually. Their different crystal structures have been determined. 1a crystallizes in the space group P21/c, 1b in Pbca and 1c in P-1. The asymmetric unit of 1c contains two independent molecules labeled A and B. Thus ZnL2 can assume at least four different molecular conformations in the solid state, namely 1a, 1b, 1c-A and 1c-B. But in the DFT calculations at the B3LYP/6-311++G (2d,p) and BP86/LanL2DZ levels 1a, 1b, 1c-A and 1c-B converge to a single structure in the gas phase. The DFT structure is found to possess a C2 axis though no symmetry constraint was imposed in the calculations. Interestingly 1a, 1b, 1c-A and 1c-B yield the same NMR spectra in solution revealing a C2 axis. So it is concluded that the gas phase DFT structure is realized experimentally only in solution. Further, our DFT calculations show that the four species are distributed along a “potential energy curve” of ZnL2. Anyway, our ZnL2 presents a case of concomitant polymorphism.

Suspect screening of maternal serum to identify new environmental chemical biomonitoring targets using liquid chromatography-quadrupole time-of-flight mass spectrometry.

The use and advantages of high-resolution mass spectrometry as a discovery tool for environmental chemical monitoring has been demonstrated for environmental samples but not for biological samples. We developed a method using liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF/MS) for discovery of previously unmeasured environmental chemicals in human serum. Using non-targeted data acquisition (full scan MS analysis) we were able to screen for environmental organic acids (EOAs) in 20 serum samples from second trimester pregnant women. We define EOAs as environmental organic compounds with at least one dissociable proton which are utilized in commerce. EOAs include environmental phenols, phthalate metabolites, perfluorinated compounds (PFCs), phenolic metabolites of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), and acidic pesticides and/or predicted acidic pesticide metabolites. Our validated method used solid phase extraction, reversed phase chromatography in a C18 column with gradient elution, electrospray ionization in negative polarity, and automated MS/MS data acquisition to maximize true positive rates. We identified “suspect EOAs” using Agilent MassHunter Qualitative Analysis software to match chemical formulas it generated from each sample run with molecular formulas in our unique database of 693 EOAs assembled from multiple environmental literature sources. We found potential matches for 282 (41%) of the EOAs in our database. Sixty-five of these suspect EOAs were detected in at least 75% of the samples, only 19 of these compounds are currently biomonitored in NHANES. We confirmed two of three suspect EOAs by LC-QTOF/MS using a targeted method developed through liquid chromatography-tandem mass spectrometry, reporting the first confirmation of benzophenone-1 and bisphenol S in pregnant women’s sera. Our suspect screening workflow provides an approach to comprehensively scan environmental chemical exposures in humans. This can provide a better source of exposure information to help improve exposure and risk evaluation of industrial chemicals.

Synthesis and Determination of the pKa Values of a Series of Bis(anilino)furazano[3, 4‐b]pyrazines

AbstractMitochondrial uncouplers such as bis(anilino)furazano[3, 4‐b]pyrazines are potentially useful as metabolic probes and as pharmaceutical treatments for obesity. The ongoing development of such molecules would be facilitated by an ability to predict and control the pKa value of the dissociable proton(s). In this work, new analogues based on the aforementioned scaffold were prepared utilising a novel method for incorporating the aniline substituents. The pKa values of these species were measured using a bracketing indicator method. The pKa values correlated well with, and showed a strong dependence on, the electronic nature of the substituent (including for those at the ortho position). The second deprotonation of these species was also evaluated, with a similar trend noted.

Homoleptic copper(II) complexes of an osazone. Reversal of the coordination ability of hexafluorophosphate and perchlorate anions

Using the 1:1 condensate of benzil and 2-hydrazinopyridine as the ligand LH (H: dissociable proton), three copper(II) complexes of the type [Cu(L)(LH)]ClO4 (1), Cu(L)(LH)PF6 (2) and CuL2 (3) are synthesized. From the X-ray crystal structures, it is found that 1 is distorted square pyramidal, whereas complex 2 in distorted octahedral via coordination of PF6− anion to the metal with a Cu(II)F bond distance of 2.722(3)Å. Although ClO4− is more coordinating than PF6−, a reversal of their coordinating ability is observed here. The CuN bond trans to CuF is somewhat longer (2.304Å). Complex 3 is a distorted octahedral homoleptic neutral mer complex. In 3 two axial CuN bond lengths are shorter (1.967Å and 1.978Å) than the equatorial one giving rise to a compressed octahedron. EPR spectrum of 1 is isotropic (g=2.057), but g|| (2.138)>g⊥ (2.027) in 2 showing Jahn-Teller elongation. On the other hand, in 3, g||<g⊥ (1.986, 2.112), which is another type of manifestation of the Jahn-Teller effect. In the density functional theory calculations, the SOMO of 2 shows a (dx2−y2)1 ground state in contrary to 3 where (dz2)1 is the ground state. Thus experimental and theoretical results are in one-to-one-correspondence. In cyclic voltammetry at an Au electrode whose surface is modified by thiocyanate, 3 displays an irreversible one-electron oxidation with an anodic peak potential of 0.98V vs normal hydrogen electrode.

Optoacoustic analysis of the distribution of polymeric micelles in tumors

Reactions of bis(acetylacetonato)oxovanadium(IV) [VO(acac)2] with isolated or in-situ generated α-diketone bis(para-R-benzoylhydrazones) (H2Ln (n = 1–6), where 2H represent the two dissociable amide protons) in methanol or chloroform–methanol (1:3) mixture afford six novel oxovanadium(V) complexes of formula [VO(acac)(Ln)] (1–6) in 51–64% yields. All the complexes have been characterized by elemental analysis, mass spectrometric, solution electrical conductivity, various spectroscopic (IR, UV–Vis, and 1H NMR) and cyclic voltammetric measurements. The complexes are brown in color. They are diamagnetic and non-electrolytes. Molecular structures of all six complexes have been determined by single crystal X-ray crystallography. The metal center in each complex is in a distorted pentagonal-bipyramidal N2O5 coordination sphere. The fused 5,5,5-membered chelate rings forming ON2O-donor (Ln)2− and one of the acetylacetonate-O form a N2O3 pentagonal plane around the vanadium atom, while the second acetylacetonate-O and the oxo atom occupy the two axial positions. In the crystal lattice, the complexes form one-dimensional chain-, ladder- and ribbon-like supramolecular structures via various types of intermolecular non-covalent interactions such as trifurcated OH∙∙∙(O,O,O), bifurcated CH∙∙∙O∙∙∙HC and CH∙∙∙(O,O), simple CH∙∙∙O, π−π, CH∙∙∙π and O∙∙∙O interactions. The spectroscopic features of 1–6 are consistent with their molecular structures. All the complexes are redox active and display a quasi-reversible to irreversible vanadium(V) to vanadium(IV) reduction in the potential range −0.80 to −0.92 V (vs. Ag/AgCl).

Influence of structural elements on iron(III) chelating properties in a new series of amino acid-derived monohydroxamates

Abstract A series of amino acid-derived monohydroxamate compounds A1 – A7 was synthesized and characterized for their coordination properties of Fe(III). The series varies in their skeletal lengths and compositions; some compounds lack external substituents, others are substituted with external functional amino or carboxylic groups, or alternatively inert methyl. Undertaken investigations allowed the determination of stoichiometry, stability constants and spectroscopic parameters of formed ferric complexes. Incorporation of an external functional group with a dissociable proton affects the coordination behavior; the presence of carboxylic or amino groups hampers the formation of mono-, di- and trihydroxamate ferric complexes of presented compounds. The differences in Fe(III) affinity of the monohydroxamates vs trihydroxamates was reflected by the stability constants and pFe, indicating the superior stability of hexadentate complexes.

N-(acyl)- $$\textit{N}^\prime $$ N ′ -(ferrocenylidene)hydrazines and their nickel(II) complexes: Syntheses, structures and physical properties

The Schiff bases N-(acyl)- $$N^{\prime }$$ -(ferrocenylidene)hydrazines (HFcah (1) and HFcbh (2), where acyl = acetyl in 1 and benzoyl in 2 and H represents the dissociable amide proton) were synthesized in high yields (74 and 81%) by condensation reactions of equimolar amounts of ferrocene-carboxaldehyde and the corresponding acylhydrazines in presence of acetic acid in refluxing methanol. Reactions of $$\text {Ni(OAc)}_{2} \cdot \hbox {4H}_{2}\hbox {O}$$ , the Schiff bases (1 and 2) and $$\hbox {NaOAc}\cdot \hbox {3H}_{2}\hbox {O}$$ in 1:2:4 mole ratio in refluxing methanol afforded the diamagnetic iron(II)-nickel(II)-iron(II) species [ $$\text {Ni(Fcah)}_{2}$$ ] (3) and [ $$\text {Ni(Fcbh)}_{2}$$ ] (4) in 60 and 68% yields, respectively. Both Schiff bases and the two trinuclear complexes were characterized by elemental (CHN) analysis, mass spectrometric, various spectroscopic (IR, UV-Vis and $$^{1}\hbox {H}$$ NMR) and cyclic voltammetric measurements. Molecular structures of 2, 3 and 4 were determined by single crystal X-ray diffraction studies. The cyclopentadienide rings in the ferrocene moieties are essentially in eclipsed conformation in all three structures. Deprotonated Schiff base ligands in each complex ( $$\hbox {Fcah}^{-}$$ in 3 and $$\hbox {Fcbh}^{-}$$ in 4) act as five-membered chelate ring forming azomethine-N and amidate-O donors and assemble a square-planar $${ trans}\hbox {-N}_{2}\hbox {O}_{2}$$ coordination environment around the nickel centre. The redox active 1–4 exhibit an iron centred redox couple in the potential range 0.23–0.50 V (vs. Ag/AgCl). N-(acetyl/benzoyl)- $$N^{\prime }$$ -(ferrocenylidene)hydrazines (HFcah and HFcbh) and their diamagnetic nickel(II) complexes [ $$\hbox {Ni(Fcah)}_{2}$$ ] and [ $$\hbox {Ni(Fcbh)}_{2}$$ ], each containing a bent iron(II)-nickel(II)-iron(II) array, were synthesised and characterised by analytical, spectroscopic and electrochemical measurements. Molecular structures of HFcbh and the two trinuclear complexes have been confirmed by X-ray crystallography.

On bonding in bis(dimethylglyoximato)nickel(II)

The Ni(II) complex of dimethylglyoxime (dmgH where H is dissociable oxime proton) occurs as an infinite chain of the discrete molecule Ni(dmgH)2 with a NiNi distance of 3.24Å. Density Functional Theoretical calculations, using LanL2DZ and 6-31+G(2d,p) as two sets of basis functions and M06-2X as the functional, show that the dimeric unit [Ni(dmgH)2]2 has a cohesive energy more than 20kcalmol−1. This energy is almost same in the corresponding hypothetical zinc analogue. Since there cannot be any metal-metal bond in [Zn(dmgH)2]2, possibility of a NiNi bond in [Ni(dmgH)2]2 is precluded. This is supported by qualitative m.o. analyses also. Further the NiNi bond distance is almost same as the sum of the van der Waals radii of the two Ni atoms as designated by Bondi which is 3.26Å. It is found that the binding energy in [Ni(dmgH)2]2 arises from aromatic-aromatic interactions and that in [Zn(dmgH)2]2 due to π-π interactions between the ligand frameworks. An energy decomposition analysis show that electrostatic and dispersion effects govern the cohesive energy in [Ni(dmgH)2]2 and [Zn(dmgH)2]2. Their numerical values are comparable. The orbital interactions in them are relatively less. [Zn(dmgH)2]n is not stable for n>2. There are two types of chelate rings in Ni(dmgH)2 monomer – a five membered one with six π electrons and a six membered one having ten σ electrons. Consequently the smaller chelate ring is π-aromatic and the other one σ-aromatic. Such a conclusion is drawn from considerably negative values of NICS(0) (Nucleus Independent Chemical Shift at the centroid of a ring) for the two chelates. The corresponding chelates in [Zn(dmgH)2]2 are not aromatic.

Oxidation chemistry of C–H bond by mononuclear iron complexes derived from tridentate ligands containing phenolato function

A family of phenolato-based nonheme mononuclear iron(III) complexes, [FeIII(Ln)Cl2](1–4) (n=1, 2, 3, and 4) derived from tridentate ligands LnH (where L1H=2-((2-phenyl-2-(pyridine-2-yl)hydrazono)methylphenol, L2H=2-((2-phenyl-2-(pyridine-2-yl)hyrazono)nitrophenol, L3H=4-methoxy-2-((2-phenyl-2-(pyridin-2-yl)hydrazono) methyl) phenol and L4H=2,4-di-tert-butyl-6-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol and H was dissociable proton) were synthesized and characterized by different spectroscopic methods. The molecular structure of [Fe(L4)Cl2](4) was determined by X-ray crystallography. The electronic structures of complexes 2 and 4 were investigated by DFT and TD-DFT calculations. All complexes were employed as catalyst for C–H bond oxidation utilizing H2O2 as an oxidant. Effect of the substituents on the phenyl ring containing phenolato function was scrutinized for efficiency and selectivity of the oxidation process. Role of key intermediate FeIII–OOH and FeIVO was also be described.

Ligand effects on nitrate reduction by zero-valent iron: Role of surface complexation

Surface passivation is a key limiting factor in the application of zero-valent iron (ZVI) for water remediation. Addition of ligands is a useful approach to overcome this issue. In this work, a small amount of acetylacetone (AA) (0.5 mM) was found highly efficient to enhance the reduction of nitrate by ZVI at near neutral conditions (pH 6.0) with the formation of considerable black coating on ZVI. At an initial nitrate concentration of 20 mg N/L, the pseudo first-order reduction rate constant of nitrate in the ZVI-AA-NO3− system was 0.0991 h−1, which was 52 times higher than that in the ZVI-NO3− system. Under otherwise identical conditions, the other five ligands, including EDTA, formate, acetate, oxalate, and phosphate, had negligible effects. Based on the pKa values of these ligands and the final species of iron, the ligand effects on nitrate reduction by ZVI were summarized from three aspects: (1) the ability to offer potentially dissociable protons from the ligands; (2) the complexation ability to eliminate iron (hydr)oxide precipitates from the surface of ZVI; and (3) the ability to lower down the redox potentials of iron species. The good performance of AA in these three aspects makes it advantage over the other ligands. A cycle test up to six runs demonstrates that AA could continuously take effect in the ZVI system. The results here point out the potential of AA as an effective ligand in ZVI system for enhanced contaminant transformation.

Synthesis and Speciation-Dependent Properties of a Multimetallic Model Complex of NiSOD That Exhibits Unique Hydrogen-Bonding

The complex Na3[{NiII(nmp)}3S3BTAalk)] (1) (nmp2- = deprotonated form of N-(2-mercaptoethyl)picolinamide; H3S3BTAalk = N1,N3,N5-tris(2-mercaptoethyl)benzene-1,3,5-tricarboxamide, where H = dissociable protons), supported by the thiolate-benzenetricarboxamide scaffold (S3BTAalk), has been synthesized as a trimetallic model of nickel-containing superoxide dismutase (NiSOD). X-ray absorption spectroscopy (XAS) and 1H NMR measurements on 1 indicate that the NiII centers are square-planar with N2S2 coordination, and Ni-N and Ni-S distances of 1.95 and 2.16 Å, respectively. Additional evidence from IR indicates the presence of H-bonds in 1 from the approximately -200 cm-1 shift in νNH from free ligand. The presence of H-bonds allows for speciation that is temperature-, concentration-, and solvent-dependent. In unbuffered water and at low temperature, a dimeric complex (1A; λ = 410 nm) that aggregates through intermolecular NH···O═C bonds of BTA units is observed. Dissolution of 1 in pH 7.4 buffer or in unbuffered water at temperatures above 50 °C results in monomeric complex (1M; λ = 367 nm) linked through intramolecular NH···S bonds. DFT computations indicate a low energy barrier between 1A and 1M with nearly identical frontier MOs and Ni-ligand metrics. Notably, 1A and 1M exhibit remarkable stability in protic solvents such as MeOH and H2O, in stark contrast to monometallic [NiII(nmp)(SR)]- complexes. The reactivity of 1 with excess O2, H2O2, and O2•- is species-dependent. IR and UV-vis reveal that 1A in MeOH reacts with excess O2 to yield an S-bound sulfinate, but does not react with O2•-. In contrast, 1M is stable to O2 in pH 7.4 buffer, but reacts with O2•- to yield a putative [NiII(nmp)(O2)]- complex from release of the BTA-thiolate based on EPR.

Electrodeposition of compact zinc from the hydrophobic Brønsted acidic ionic liquid-based electrolytes and the study of zinc stability along with the acidity manipulation

Compact crystalline zinc was electrodeposited on stainless-steel electrode (SS) via potentiostatic/galvanostatic electrolysis from the hydrophobic Brønsted acidic ionic liquid, protonated betaine bis((trifluoromethyl)sulfonyl)imide (IL [Hbet][TFSI]), −based electrolytes containing ZnCl2 or ZnO under argon or ambient air atmosphere. Approximate 10wt% of propylene carbonate and water, respectively, were used as the co-solvents for [Hbet][TFSI] to form the IL-based electrolytes. The efficiency of zinc deposition/stripping, which is significantly affected by the Brønsted acidity of the IL-based electrolytes, was studied at glassy carbon electrode (GC) to evaluate the stability of the zinc electrodeposits along with the electrolyte acidity. The stability is very poor for the zinc electrodeposits obtained from ZnCl2 solution. However, it increases with increasing the quantity of ZnO or urea in the electrolytes; the former neutralize the dissociable protons in [Hbet] cations to form water, and the latter may form H-bonding with [Hbet] or be protonated to form the weakly acidic cations [HUrea]. Both suppress the reaction between the Zn electrodeposits and protons. The stability of the Zn electrodeposits, therefore, can be improved via the manipulation of the IL acidity.

The effect of an ancillary ligand proton on the photophysical properties of some RuIIN6cores: a proton valve

The proton of the ancillary ligand (lig) in [Ru(bpy/phen)2(lig)]2+decides whether a Ru(ii)N6core will be emissive or not.

Ruthenium Carbonyl Complexes with 4-R-Benzaldehyde Thiosemicarbazone as an Ancillary Ligand: Synthesis and, Structural, Spectral and Electrochemical Properties

Reaction of 4-R-benzaldehyde thiosemicarbazone (denoted as HL-R; where H stands for the dissociable acidic proton and R (R = OCH3, CH3, H, Cl and NO2) for the substituents) with [Ru(CO)2Cl2]n in toluene in the presence of triethylamine affords a group of yellow complexes of the type [Ru(CO)2(L-R)2]. Structure of [Ru(CO)2(L-NO2)] has been determined by X-ray crystallography. In [Ru(CO)2(L-R)2] complexes, the thiosemicarbazone ligands are bound to the metal center as monoanionic bidentate N,S-donor forming four-membered chelate ring. All the complexes are diamagnetic, and show characteristic 1H NMR signals. The [Ru(CO)2(L-R)2] complexes show intense absorptions in the visible and ultraviolet regions, which have been analyzed by DFT calculations. Cyclic voltammetry on the complexes shows two irreversible oxidations near 0.87 and 1.28 V versus SCE, and an irreversible reduction around −1.24 V versus SCE.