Reference value standards for pH measurements in 5, 15 and 30% (w/w) acetonitrile/water solvent mixtures at temperatures from 288.15 to 308.15 K

Reference value standards, pH (RVS), for 0.05 mol kg^?1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 5, 15 and 30% (w/w) acetonitrile/water mixed solvents at temperatures from 288.15 to 308.15 K are determined from reversible e.m.f. measurements of the cell Pt¦H₂¦KHPh + KCl¦AgCl|Ag|Pt. Values of the first ionisation constant of o-phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in these mixed solvents are also determined from analogous measurements. The consistency of the results is analysed by multilinear regression of the quantity p(a_HγCl) as a function of both solution composition and temperature. The standard pH (RVS) values determined are given by the equation pH (RVS) = 4.0080 + 6.330x + 16.177x² ? 115.3x³ + 0.3089u ? 201.0ux² + 909ux³ + 13.04v, where x is the mole fraction of acetonitrile in the mixed solvent, u = z/(1 + z), v = [ln(1 + z) ? u], z = (T ? θ)/θ, and θ = 298.15 K.     

Standard pH values for potassium hydrogenphthalate reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water mixed solvents at temperatures from 288.15 to 318.15 K

Standard pH(S) values for 0.05 mol kg^?1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H₂|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(a_Hγ_Cl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w³ - 14.95zw² + 27.1zw³, where w is the weight fraction of dioxane in the solvent mixture,z = (T –θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H₂|H₂Ph + KHPh + KCl|AgCl|Ag|Pt.     

Standards for pH measurements and first ionization constants ofo-phthalic acid. Methylcellosolve-water solvent mixtures from −10 to 45°C

From reversible emf measurements of the cell Pt/H₂/KHPh+KCl/AgCl/Ag/Pt, reference value pH-metric standards, pH _RVS , for 0.05 mol-kg^–1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 20, 50, and 80 wt % methylcellosolve (2-methoxyethanol, CH₃O-CH₂CH₂OH)-water solvent mixtures from –10 to +45°C, have been determined in compliance with the criteria endorsed by IUPAC. The corresponding values of the first ionization constant ofo-phthalic acid (H₂Ph, benzene-1,2-dicarboxylic acid), which is a key quantity for the acquisition of pH _RVS standards, have been determined from emf measurements of the reversible cell Pt/H₂/H₂Ph+KHPh+KCl/AgCl/Ag/Pt.     

Ionization Constants of o-Phthalic Acid and Standard pH Values of Potassium Hydrogen Phthalate Buffer Solutions in Glycerol + Water Solvent Mixtures at Normal and Subzero Temperatures

Determination of primary standards for pH measurements in glycerol + water solventmixtures has been carried out based on reversible emf measurements of the cellPt|H₂|KHPh (m _PS) + KCl (m _Cl)|AgCl|Ag|Ptwhere KHPh denotes the potassium hydrogen phthalate buffer solution of molalitym _PS = 0.05 mol-kg^–1, at glycerol mass fractions w _G = 0.2 and 0.4, within thetemperature range –10 to 40°C. A multilinear regression procedure as a functionof electrolyte molality, glycerol mass fraction w _G, and temperature T has beenapplied for the data processing leading to the values of primary standards pH_PS.These can be represented by the following regression equationpH_PS = (4.007037±0.001113) + (3.55844±0.01776)x _G+(0.39622±0.01410)z + (4.3084±0.3377)z ²– (50.66±10.53)x _G z ² + (457.10±78.48)x _G ² z ²where z = (T – 298.15)/298.15. Parallel values of the first ionization constantof o-phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid, the parent acid of KHPh),which are essential for the above calculations, have been determined fromreversible emf measurements of the cellPt|H₂|H₂Ph (m ₁) + KHPh (m ₂) + KCl (m ₃)|AgCl|Ag|Ptover the range of solvent composition and temperatures mentioned above.     

Studies on the Equilibria of α-Phthalic and Phosphoric Acids in Mixed Methanol — Water Mixture (50% w/w)

The secondary dissociation constants of α-phthalic and phosphoric acids have been determined in 50% w/w methanol-water mixture from the e.m.f measurements of the cell of the type: Pt; H₂(1 atm), M₂A(m), MHA(m), MCl, AgCl; Ag at different temperatures (288.15–308.15 K) and at different ionic strengths. The thermodynamic values ΔG°, ΔH°, ΔS° for the respective equilibria are estimated. The possibility of using these acids as basis for some buffer solutions in 50% methanol – water mixture is discussed.     

Thermodynamic studies of hydriodic acid in ethylene glycol-water mixtures from electromotive force measurements

The standard potentials of the Ag—AgI electrode in twenty ethylene glycol—water mixtures covering the whole range of solvent composition have been determined from the e.m.f. measurements of the cell Pt¦H₂(g, 1 atm)¦HOAc (m ₁), NaOAc (m ₂), KI(m ₃), solvent¦AgI¦Ag at nine different temperatures ranging from 15 to 55°C. The temperature variation of the standard e.m.f. has been utilized to compute the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HI, and the standard thermodynamic quantities for the transfer of HI from the standard state in water to the standard states in the respective solvent media. The chemical effects of solvents on the transfer process have been obtained by subtracting the electrostatic contributions from the total transfer quantities. The results have been discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.     

Thermodynamic properties of o-phthalic acid and its products of dissociation at 0–200°C and 1–5000 bar

Values of the pH for four solutions in a KHPh-HCl-KOH system, where Ph denoting C₈O₄H₄, are measured at 25–70°C depending on pressure (1–1000 bar). The experimental results and the available literature data are processed on the base of Helgeson-Kirkham-Flowers (HKF) equation of state [1] and the GIBBS, OptimA, and OptimB programs from the HCh software package [2]. The obtained standard thermodynamic properties and HKF parameters of H₂Ph_aq, HPh^?, and Ph^2? aqueous species, provides calculation of the pH of phthalate buffers in a wide range of temperatures (up to 200°C) and pressures (up to 5 kbar). The calculated values for the biphthalate buffer (0.05m KHPh) correspond to the IUPAC recommendations (at 0–50°C and 1 bar) with an accuracy of 0.005 pH units, and to the values of pH measured in this study at elevated Tp parameters (25–70°C and pressures of up to 1 kbar) within the limits of ±0.02 pH units.     

Standard pH values for phosphate buffer reference solutions in acetonitrile-water mixtures up to 50% (m/m)

Reference pH_ps values for 0.025 mol/kg potassium dihydrogen phosphate + 0.025 mol/kg disodium hydrogen phosphate primary standard buffer solutions in 10, 30, 40 and 50% (m/m) acetonitrile-water mixtures at 298.15 K have been determined from reversible e.m.f. measurements of the cell Pt/Ag/AgCl/primary standard buffer + KCl in acetonitrile-water/glass electrode. The consistency of the results is confirmed by multilinear regression analysis of the pH_ps values obtained for each solution composition. Considering the high number of possible acetonitrile-water mixtures, the methodology of linear solvation energy relationships (LSER) was applied and pH_ps data have been correlated with the Kamlet-Taft solvatochromic parameters of the acetonitrile-water mixtures over the whole of the experimental range.     

Carbon‐Nanotube‐Supported Bio‐Inspired Nickel Catalyst and Its Integration in Hybrid Hydrogen/Air Fuel Cells

A biomimetic nickel bis‐diphosphine complex incorporating the amino acid arginine in the outer coordination sphere was immobilized on modified carbon nanotubes (CNTs) through electrostatic interactions. The functionalized redox nanomaterial exhibits reversible electrocatalytic activity for the H₂/2 H⁺ interconversion from pH 0 to 9, with catalytic preference for H₂ oxidation at all pH values. The high activity of the complex over a wide pH range allows us to integrate this bio‐inspired nanomaterial either in an enzymatic fuel cell together with a multicopper oxidase at the cathode, or in a proton exchange membrane fuel cell (PEMFC) using Pt/C at the cathode. The Ni‐based PEMFC reaches 14 mW cm⁻², only six‐times‐less as compared to full‐Pt conventional PEMFC. The Pt‐free enzyme‐based fuel cell delivers ≈2 mW cm⁻², a new efficiency record for a hydrogen biofuel cell with base metal catalysts.     

Actinide cyanometallates

Simple salts of the tetracyanoplatinate (TCP) anions with the general formula M[Pt(CN)₄] _x ·H₂O have been described for over 200 years. A major structural feature of these compounds are pseudo one dimensional Pt···Pt interactions between the square planar tetracyanoplatinate anions. These interactions form quasi one-dimensional chains in the solid state and are believed to be the source of their unique spectroscopic and emission properties. The lanthanides offer the ability to tune the Pt···Pt spacing of these pseudo one dimensional chains, predictably by taking advantage of the lanthanide contraction. Here, we describe the emission and structural characteristics of new actinide tetracyanometallates.     

EPR kinetic study of the reactions of F and Br atoms with H2CO

The absolute rate constants of the reactions F + H₂CO → HF + HCO (1) and Br + H₂CO → HBr + HCO (2) have been measured using the discharge flow reactor-EPR method. Under pseudo-first-order conditions (¦H₂CO¦?¦F¦or¦Br¦), the following values were obtained at 298 K: k₁ = (6.6 ± 1.1) × 10^?11 and k₂ = (1.6± 0.3) × 10^?12, Units are cm³ molecule^?1s^?1. The stratospheric implication of these data is discussed and the value obtained for k makes reaction (2) a possible sink for Br atoms in the stratosphere.     

Enthalpies of reaction of bis(triphenylphosphine)(trans-stilbene)platinum(0) with diphenylcyclopropenone and benzocyclobutenedione

Enthalpies, ΔH(1) ?94.8 ± 6.0 and ΔH(6) ?57.1 ± 5.1 kJ mol^?1, of the following reactions have been measured calorimetrically [Pt(trans-stilbene)(PPh₃)₂](s) + dpcp(g) → (PPh₃)₂Pt(dpcb)(s) + trans-stilbene(g) (1) [Pt(trans-stilbene)(PPh₃)₂](s) + bcbd(g) → (PPh₃)₂Pt(bcpd)(s) + trans-stilbene (g) (6) where dpcp is diphenylcyclopropenone, (PPh₃)₂Pt(dpcb) is (1,1-bistriphenylphosphine)platinadiphenylcyclobutenone, (PPh₃)₂$\text{PtC(Ph)C(Ph)C}$O, bcbd is benzocyclobutene-1,2-dione and (PPh₃)₂Pt(bcpd) is (1,1-bistriphenylphosphine)platinabenzocyclopentanedione,

. It is concluded that the five-membered platinacyclo ring system in (PPh₃)₂Pt(dpcb) is not heavily strained.     

Synthetic and spectroscopic studies of some mono-hydrido-bridged complexes of platinum(II)

The mono-hydrido-bridged complexes (PEt₃)₂(Ar)Pt(μ₂-H)Pt(Ar)(PEt₃)₂]-[BPh₄] (Ar = Ph, 4-MeC₆H₄ and 2,4-Me₂C₆H₃) have been obtained by treating trans-[Pt(Ar)(MeOH)(PEt₃)₂][BF₄] with sodium formate and Na[BPH₄]. The cations [PEt₃)₂(Ar)Pt(μ₂-H)Pt(Ar^b')(PEt₃)₂]^b+ (Ar = Ph and Ar^b' - 2,4-Me₂C₆H₃ and 2,4,6-Me₃C₆H₂ have bee identified in solution. Their ^b1H- and ^b31P-NMR data are reported. The X-ray crystal structure of [(PEt₃)₂(Ph)Pt(μ₂-H)Pt(Ph)(PEt₃)₂][BPh₄] is reported.     

Transmetallation reactions of [Sn(R)2(Ph2PC6H4-2-S)2] with metal complexes of the Group 10: Stereoselective synthesis of cis-[M(Ph2PC6H4-2-S)2] (M=Ni, Pd, Pt)

The complexes cis-[M(Ph₂PC₆H₄-2-S)₂] M=Ni, Pd, Pt were stereoselectively synthesized by transmetallation reactions of [M(Cl)₂(NCC₆H₅)₂] M=Pd, Pt or NiCl₂·6H₂O with [Sn(R)₂(Ph₂PC₆H₄-2-S)₂] R=Ph, ⁿBu or ^tBu. The conformation of the Pd and Pt derivatives being unequivocally confirmed by single crystal X-ray diffraction studies showing both metal centers to be into a slightly distorted square planar environment, the main distortion being due to the steric hindrance caused by the aromatic rings in the phosphine moiety.     

Adsorption of acetone on the mercury electrode from H2O+(CH3)2CO+HCl solutions

The adsorption of acetone on a mercury electrode from (CH₃)₂CO+H₂O+HCl solutions has been studied using a thermodynamically rigorous procedure. The chemical potential of the supporting electrolyte has been kept constant by using the concentrations corresponding to the constant e.m.f. of the cell with electrodes reversible to each of the ions in the solutions. It is suggested that the molecule is to some extent oriented with the hydrocarbon part towards mercury. The composition of the surface layer has been calculated.     

RuP2‐Based Catalysts with Platinum‐like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values

Highly active, stable, and cheap Pt‐free catalysts for the hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing HER electrocatalysts with Pt‐like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we design and synthesize a novel N,P dual‐doped carbon‐encapsulated ruthenium diphosphide (RuP₂@NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP₂@NPC not only has Pt‐like HER activity with small overpotentials at 10 mA cm⁻² (38 mV in 0.5 m H₂SO₄, 57 mV in 1.0 m PBS and 52 mV in 1.0 m KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work adds to the growing family of transition‐metal phosphides/heteroatom‐doped carbon heterostructures with advanced performance in HER.     

Status and problems of standardization of pH scales for controls in different media. Reference value standards in ethylene glycol/water mixed solvents

Summary One of the most complex establishments of standards in quality control is that for the measurement of acidity, the pH. Not only is this complexity linked with the environment or the matrix considered (solutions from chemical laboratories or industries, biophysiological fluids, sea waters, estuarine waters, freshwaters, acid rains, etc.) but also with the solvent type (water, nonaqueous solvents, aqueous-organic solvent mixtures). The results are distinct pH scales which, for each solvent considered, are articulated on one reference value standard (pH_RVS) plus a group of primary standards (pH_PS) and/or operational standards (pH_os), as specified in recent IUPAC recommendations. Such specifications ensure that the above standards be determined according to the same electrochemical principles and procedures and be accurate typically to ±0.002 in pH. However, the acquisition and availability of such standards, though rapidly expanding, are hitherto limited to a few nonaqueous solvents or aqueous-organic solvent mixtures. Within this context, the determination of pH_RVS in ethylene glycol/water mixtures, based on electromotive force measurements of the cell Pt|H₂|RVS Buffer + KCl|AgCl|Ag|Pt over a range of temperatures and solvent compositions is here described. Anyway, the comparability of pH scales in different solvent media (and even in different environments) depends on the uncertain determinability of the primary medium effect upon the H⁺ ion. Finally, the predictability of the above standards, whithin acceptable reliability limits, for hitherto unexplored solvent media has been recently assessed in terms of such qualifying physicochemical quantities as solvent composition, dielectric constant and temperature. Status, applications and problems related to the above points are here analysed.     

cis‐Di­phenyl­bis(1,3,5‐tri­aza‐7‐phospha­adamantane‐κP)platinum(II)

The structure of the title compound, [Pt(C₆H₅)₂(C₆H₁₂N₃P)₂] or [Pt(Ph)₂(PTA)₂] (where Ph is phenyl and PTA is 1,3,5‐tri­aza‐7‐phosphaadamantane), is discussed. Selected geom­etric parameters are: Pt—P = 2.2888 (16) and 2.2944 (17) Å, Pt—C = 2.052 (5) and 2.064 (6) Å, C—Pt—C = 84.6 (2)° and P—Pt—P = 99.28 (6)°. The effective cone angle for the PTA ligands was calculated as 113°.     

Standard pH values for standardization of potentiometric sensors in 10% (w/w) acetonitrile-water mixtures

Reference value standards, pH(s) in 10% (w/w) acetonitrile-water solvent mixtures for 11 reference buffer solutions have been determined from reversible emf measurements of the cell Pt/Ag/AgCl/standard buffer + KCl, in acetonitrile-water/glass electrode, at 298.15 K. Values of ionization constants, required for above calculations, have been determined from reversible emf measurements of the cell Pt/Ag/AgCl/HA + A + KCl, in acetonitrile-water/glass electrode, in the same solvent composition and temperature.     

Stereochemical,biochemical and ligation behaviour of divalent platinum complexes of sulfur and nitrogen donor agents

Divalent Pt complexes of o-FC₆ H₄ C(H)NNC(SH)SCH₂ Ph(L¹H) and o-FC₆ H₄ C(Me)NNC(SH)SCH₂ Ph(L ²H) have been synthesized and characterized thoroughly by analytical data, conductance measurements, molecular weight determinations, magnetic measurements, i.r., electronic, ¹H-n.m.r. and ¹⁹F-n.m.r. spectral studies. The spectral data are consistent with a square planar geometry around Pt^IIin which the ligand acts as a neutral bidentate and monobasic bidentate ligand coordinating through nitrogen and sulfur atoms. Ligands and their metal complexes were tested against certain microorganisms to assess their antimicrobial properties and the results are indeed positive.