Formation Of Chloride Complexes Research Articles

Trace Element Partitioning Between Saline Aqueous Fluids and Subducted Metasediments, and the Origin of the “Sediment Fingerprint” in Arc Magmas

AbstractIsotopic and elemental signatures in arc magmas bear similarities to marine sediments from the forearc. Partial melts of subducted sediments were previously invoked as the predominant carrier of material between the slab and mantle wedge, whereas aqueous fluids were deemed too inefficient at mobilizing trace elements to account for arc magma compositions. However, trace element solubility in aqueous fluids may be significantly affected by the formation of chloride complexes. We introduced NaCl into the sediment‐H2O system, and re‐investigated trace element partitioning between aqueous fluids and metasediments in a series of piston cylinder experiments at 2.5–4.5 GPa and 600–700°C. The diamond trap method was employed to separate the fluids, which were analyzed in the frozen state. Trace element compositions of fluids and all solid phases were obtained by LA‐ICP‐MS. We combined our data with published literature to demonstrate that saline fluids and sediment melts have a comparable efficiency in extracting incompatible elements from subducted sediments, producing similar element fractionation during mobile phase expulsion. Accessory phases such as allanite may only be stable in particularly Rare Earth Elements‐enriched lithologies. The Sr, Pb and Nd isotopic signatures of arc magma suggest that the mantle wedge is infiltrated by mobile phases derived from both the sediment and basalt sections of the subducted oceanic crust. Up to several percent of either sediment‐derived saline fluid or melt can account for the isotopic and elemental compositions of most arc magma. Geochemical similarities between arc magma and forearc sediments are not necessarily evidence of slab melting.

Relation between Road-Salt Application and Increasing Radium Concentrations in a Low-pH Aquifer, Southern New Jersey

The Kirkwood–Cohansey aquifer in southern New Jersey is an important source of drinking-water supplies, but the availability of the resource is limited in some areas by high concentrations of radium, a potential carcinogen at elevated concentrations. Radium (226Ra plus 228Ra) concentrations from a network of 25 drinking-water wells showed a statistically significant increase over a decadal time scale (p < 0.05), with a median increase of 0.35 picocuries per liter. Increases in Ra are correlated with road-salt application rates, and we hypothesize that the correlation is causal. Geochemical processes associated with road-salt applications that can mobilize Ra into solution include competition by excess sodium for sorption sites and formation of chloride complexes (RaCl+ and RaCl2). The largest increases in Ra were in groundwater with low pH (≤5), which is an indirect surrogate for low cation-sorption capacity. Correlations with other potential anthropogenic causes for the increase in Ra were not observed, further suggesting a road-salt effect. Given the significant increase in Ra concentrations in this drinking-water source, the known carcinogenic risks from Ra, the direct link to road-salt application, and the likelihood for continued increases, additional monitoring is necessary in areas with similar hydrogeologic and geochemical settings.

Synthesis, structural diversity, luminescent properties and antibacterial effects of cadmium(II) and silver(I) coordination compounds with bis(1,2,3-benzotriazol-1-yl)alkanes

A series of bis(benzo-1,2,3-triazolyl)alkanes were prepared by the reaction of 1,2,3-benzotriazole with the corresponding dibromoalkanes. Individual isomers of these flexible polydentate ligands were separated by selective copper(II) chloride complex formation. Seven new coordination compounds of 1,3-bis(benzo-1,2,3-triazol-1-yl)propane (L3), 1,4-bis(benzo-1,2,3-triazol-1-yl)butane (L4) and 1,6-bis(benzo-1,2,3-triazol-1-yl)hexane (L6) with cadmium(II) or silver(I) nitrates were prepared, characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis and luminescence studies. It was found that depending on the solvent used, cadmium(II) nitrate forms discrete binuclear complex with the ligand L3 in acetone and 1D coordination polymer in acetonitrile. Ligands L4 and L6 with longer linkers formed 2D coordination polymers with silver nitrate both in acetone and acetonitrile. Silver coordination polymer with L6 demonstrated bactericidal effect towards Staphylococcus albus, Pseudomonas aeruginosa and Klebsiella pneumonia bacteria.

AN SKP and EIS study of microporous nickel-chromium coatings in copper containing electrolytes

The corrosion behaviour of microporous nickel-chromium systems was studied by means of conventional electrochemical techniques and localized ones using two chloride based electrolytes with and without cupric ions in their composition. The conscious combination of different methodologies using these techniques has provided valuable information about the corrosion process. Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy (EIS) measurements were performed in bulk solution, whilst Scanning Kelvin Probe (SKP) measurement were carried out using two methodologies: i) electrolyte droplets monitoring (measuring simultaneously potential and droplet height with time), and ii) potential maps of dried surfaces that previously were exposed to droplets. Further characterization was done based on the morphology of the attack and composition on the surface by Optical Microscopy (OM), Field Emission- Scanning Electron Microscope (FE-SEM) and X-ray Photoelectron Spectroscopy (XPS) together with the analysis of electrolyte composition with time by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Results have shown the harmful effect of Cu2+ cations in the corrosion resistance and a different morphological impact on the surface. Such negative effect has revealed a new time constant at high frequency in the impedance diagrams as well as an abrupt potential decrease (due to a change in the cathodic reaction involved: Cu2+ + e− ↔ Cu+ takes place) using SKP droplet test. Apparently, Cu+ species were stabilized in bulk solution by the formation of chloride complexes, as was confirmed by the precipitation of a white CuCl compound during droplet evaporation, pointing out the key role of Cu+ in the corrosion process.

Early stages of tin bronze corrosion in neutral aqueous chloride media: Electrochemical and FTIR investigations

The corrosion behavior of tin bronze alloy equivalent to a Punic one was investigated in aqueous 0.5 M chloride electrolyte using potentiodynamic measurements. The electrochemical results showed selective dissolution of the major alloy component reflecting a decuprification process. FTIR characterization of the patina anodic layers showed the presence of various dehydrated and hydrated tin compounds with a few copper species suggesting the patina type I formation on the Cu10Sn bronze alloy. A kinetic model for the Cu10Sn bronze alloy dissolution in the chloride solution was developed. The reaction order with respect to chloride content was determined for the Cl− halide concentration domains. The low order value (about 0.22) was attributed to the Cl− adsorption intermediate step. The high reaction order value (about 2) reflected two determining steps of cuprous chloride complex formation. Two behaviors for the material were evidenced when varying the temperature. The values of the activation energy Ea, activation enthalpy ΔH* and activation entropy ΔS* were calculated and discussed.

Decreased mobility of heavy metals in Haihe River sediments: The possible role of tide gate

The impact of tide gate on heavy metal mobility in Haihe River sediments was studied in a laboratory leaching simulation experiment. The results indicated that seawater promoted a higher release of Cd and Cu than deionized water and river water, and river water extracts high amounts of Zn. This release may be a result of both the formation of chloride complexes and ion exchange. However, the salinity induced by seawater did not significantly enhance the mobility of Pb. This implied that the mobility of Cd and Cu can be reduced by the insufficiency of the salinity when constructing tide gates in the brackish zones of an estuary. In the acidification processes, Cd and Zn were not, but Cu and Pb were, affected by an increase of salinity and ionic strength.

Antibacterial and Antihypertensive Activity OF Callus from Muskmelon (Cucumis Melo L.)

The callus of Cucumis melo L. (Muskmelon var. glamour) was studied to identify the polyphenols that have possible antihypertensive and antibacterial activity. The callus was grinded and extracted by solvent extraction. Total polyphenols were quantified using modified method of Folin-Ciocalteu and total flavonoid was quantified by modified method of Aluminium chloride complex formation. The antibacterial activity was tested against Gram-positive and Gram-negative human pathogenic bacteria using disk diffusion method and the Minimum Inhibitory Concentration (MIC) was also determined. The antihypertensive property was tested with ACE Kit. The phytohormone combination for callus induction was better when the concentration of auxin is higher than the concentration of cytokinin. Different phytohormone combination treated in media for callus induction gave different effect to the production of polyphenols of plant. The callus’s polyphenols analyzed in GC/MS indicated some polyphenols compounds that possessed antihypertensive property and involved against pathogenic bacteria.

Distribution, sources, and behavior of trace elements in the Clinton River Watershed, Michigan

The Clinton River watershed near Detroit, Michigan, USA was separated in six different land uses: agricultural, residential, mixed industrial and residential, downstream industrial, Clinton River Spillway, and Lake St. Clair, utilizing As, Cd, Cu, Ni, Pb, and Zn contents of the sediment that has median values of 3, 0.3, 15, 14, 13, and 57mgkg−1, respectively. However, trace element concentrations in the lower Clinton River rivaled those in the most contaminated watersheds of the world. Enrichment factors and principal component analysis (PCA) separated trace elements into 2 categories: anthropogenic (Cd, Cu, Ni, Pb, and Zn) and geogenic (Al, As, Ca, Fe, K, Mg, TOC) sources. PCA linked agricultural, residential, and mixed industrial and residential land uses to anthropogenic Cd, Cu, Ni, Pb, and Zn, and lake sediments to geogenic elements, organic matter and clay contents. The downstream industrial zone has a unique source signature. Trace element concentrations varied with land use. The upper Clinton River (>20km from mouth; residential land use; median concentrations up to 25mgkg−1) appeared to meet delisting criteria. Partitioning was also land use and element specific with: (1) exchangeable fraction (up to 94% of total) related to road salt and mobile chloride complex formation; (2) carbonate-bound fraction (up to 100%) resulting from Ca substitution or adsorption; (3) presence of immobile (hydr)oxide-bound fraction (up to 90%) instead of potentially mobile organic matter and sulphide-bound fraction (up to 20%); and (4) residual fraction (up to 65%) originating from geogenic and/or anthropogenic sources.

Effects of Road Salts on Heavy Metal Mobility in Two Eastern Washington Soils

Heavy metals deposited on road surfaces and transferred to roadside environments by rainfall and snowmelt runoff can have serious impacts on receiving ecosystems. Infiltration is an effective best management practice for controlling metal contamination in runoff, although metals retention within infiltration facilities depends on a number of factors, including metal species, soil characteristics, and influent water quality concentrations. In cold climates, deicing compounds have been shown to mobilize heavy metals putting receiving waters at risk. This study ascertains the effects of two widely used road salts (NaCl and MgCl 2 ) on heavy metal mobility in two eastern Washington soils. Infiltration experiments were conducted using a basic soil, exhibiting a soil pH of 8.3, taken from a highway infiltration pond site in Spokane Washington and an acidic soil, exhibiting a soil pH of 5.9, taken from an infiltration pond site in Richland Washington. Three concentrations of each salt were percolated through both soils using continuous flow soil columns. Leachate samples were collected and analyzed for dissolved metals, organic matter, and pH. Experiments were also performed without salt and used as controls. Results indicate that metal mobilization can occur by a number of mechanisms including cation exchange, chloride complex formation, and colloid dispersion (release of organic matter and/or clay that can complex metal species). Sodium chloride resulted in the largest release of copper and lead via indirect mobilization of organic matter. The magnesium salt had less of an effect on lead and copper but had a much greater effect on the mobilization of cadmium. Releases of metals during or immediately following salt application produced concentrations that ranged from 50% to 1000% greater than the concentrations released from the control experiments.

The Examination of the Activity Coefficients of Cu(II) Complexes with OH− and Cl− in NaClO4 Using Pitzer Equations: Application to Other Divalent Cations

The stability constants for the hydrolysis of Cu(II) and formation of chloride complexes in NaClO4 solution, at 25 °C, have been examined using the Pitzer equations. The calculated activity coefficients of CuOH+, Cu(OH)2, Cu2(OH)3+, Cu2(OH) 2 2+ , CuCl+ and CuCl2 have been used to determine the Pitzer parameter (β (0) , β (1) , and C i ) for these complexes. These parameters yield values for the hydrolysis constants (log 10 β 1 * , log 10 β 2 * , log 10 β 2,1 * and log 10 β 2,2 * ) and the formation of the chloride complexes (log 10 β CuCl * and $\log_{10}\beta_{\mathrm{CuCl}_{2}}^{\mathrm{*}})$ that agree with the experimental measurements, respectively to ±0.01,±0.02,±0.03,±0.06,±0.03 and ±0.07. The stability constants for the hydrolysis and chloride complexes of Cu(II) were found to be related to those of other divalent metals over a wide range of ionic strength. This has allowed us to use the calculated Pitzer parameters for copper complexes to model the stability constants and activity coefficients of hydroxide and chloride complexes of other divalent metals. The applicability of the Pitzer Cu(II) model to the ionic strength dependence of hydrolysis of zinc and cadmium is presented. The resulting thermodynamic hydroxide and chloride constants for zinc are $\log_{10}\beta_{\mathrm{ZnOH}^{+}}=-9.04\pm0.04$ and $\log_{10}\beta_{\mathrm{Zn(OH)}_{2}}=-16.90\pm0.02$ . For cadmium the thermodynamic hydrolysis constants are $\log_{10}\beta_{\mathrm{CdOH}^{+}}=-10.24\pm0.05$ and $\log_{10}\beta_{\mathrm{Cd(OH)}_{2}}=-20.42\pm0.07$ . The Cu(II) model allows one to determine the stability of other divalent metal complexes over a wide range of concentration when little experimental data are available. More reliable stepwise stability constants for divalent metals are needed to test the linearity found for the chloro complexes.

Use of Pitzer Equations to Examine the Formation of Mercury(II) Hydroxide and Chloride Complexes in NaClO4 Media

The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg2+) chloride complexes $$ \hbox{Hg}^{2+} + n\hbox{H}_{2}\hbox{O} = \hbox{Hg(OH)}_n^{(2-n)+} + n\hbox{H}^{+ } \quad\quad \beta_n $$ $$ \hbox{Hg}^{2+} + n\hbox{Cl}^{-} = \hbox{HgCl}_n^{(2-n)+ } \quad\quad \beta_i $$ have been used to calculate the activity coefficients for Hg(OH) (2–)+ and HgCl (2–)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes $$(\beta_{\rm ML}^{(0)}, \,\beta_{\rm ML}^{(1)}$$ and C ML). The values of $$\lambda_{ij}$$ and $$\zeta_{ijk}$$ have been determined for the neutral complexes (Hg(OH)2 and HgCl2). The resultant parameters yield calculated values for the measured values of log $$\beta^{\ast}$$ to ±0.01 from I = 0.1 to 3 m at 25°C. Since the activity coefficients of $$\hbox{Hg(OH)}_n^{(2-n)+}$$ and $$\hbox{HgCl}_n^{(2-n)+}$$ are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for $$\hbox{PbCl}_n^{(2-n)+}$$ complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl− in natural waters over a wide range of conditions.

EXAFS Study of Aqueous ZrIV and ThIV Complexes in Alkaline CaCl2 Solutions: Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+.

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EXAFS Study of Aqueous ZrIV and ThIV Complexes in Alkaline CaCl2 Solutions: Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+

A hitherto unknown type of aqueous complex, ternary Ca-MIV-OH complexes (M = Zr and Th), causes unexpectedly high solubilities of zirconium(IV) and thorium(IV) hydrous oxides in alkaline CaCl2 solutions (pHc = 10-12, [CaCl2] > 0.05 mol.L(-1), and pHc = 11-12, [CaCl2] > 0.5 mol.L(-1), respectively). The dominant aqueous species are identified as Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+ and characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. The number of OH- ligands in the first coordination sphere detected by EXAFS, NO = 6 (6.6 +/- 1.2) for Zr and NO = 8 (8.6 +/- 1.2) for Th, are consistent with the observed slopes of 2 and 4 in the solubility curves log [M]tot vs pHc. The presence of polynuclear hydrolysis species and the formation of chloride complexes can be excluded. EXAFS spectra clearly show a second coordination shell of calcium ions. The [Zr(OH)6]2- and [Th(OH)8]4- complexes with an unusually large number of OH- ligands are stabilized by the formation of associates or ion pairs with Ca2+ ions. The number of neighboring Ca2+ ions around the [Zr(OH)6]2- and [Th(OH)8]4- units is determined to be NCa = 3 (2.7 +/- 0.6) at a distance of RZr-Ca = 3.38 +/- 0.02 A and NCa = 4 (3.8 +/- 0.5) at a distance of RTh-Ca = 3.98 +/- 0.02 A. The Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+ complexes have first (M-O) and second (M-Ca) coordination spheres with the Ca2+ ions bound to coordination polyhedra edges.

Electrochemical Quartz Crystal Microbalance Study on Dissolution of Platinum in Acid Solutions

The influence of chloride ion on the oxidation and dissolution of platinum has been studied by using Electrochemical Quartz Crystal Microbalance (EQCM) in combination with Inductively Coupled Plasma (ICP) analysis to clarify the deterioration mechanism of platinum catalyst in the Polymer Electrolyte Fuel Cell (PEFC). Platinum was electroplated on an Au-QCM electrode in 2% H2PtCl6 solution and used as the working electrode. A mass gain of the platinum electrode was observed during anodic polarization in 0.5 M H2SO4 solution ([Cl−] free solution) due probably to the formation of Pt oxide. The oxide film was not stable in the whole range of potential used in this study. On the other hand, a mass loss due to the dissolution of Pt as chloride complex ions was observed in more positive potentials than 0.85 V vs. SHE in chloride-containing solutions. As the chloride concentration increased, platinum showed a higher dissolution rate with the formation of chloride complexes, PtCl42− and PtCl62−. The amount of dissolved PtCl62− tended to increase with the increase of anodic potential limit. The EQCM results revealed that the dissolution of Pt was accelerated when potential was cycled between cathodic and anodic limits. The ICP analysis of the solution after anodic polarization supported the results obtained by EQCM.

Ammonium chloride complex formation during downstream microwave ammonia plasma treatment of parylene-C

In this work, parylene-C is exposed to the effluent from a microwave ammonia plasma with a goal of producing primary amine groups on the parylene-C. These amine groups are desired as sites for the attachment of various biomolecules that will influence the biocompatibility of the parylene-C. Ammonia plasma treatment is an effective approach for creating amine species on polymers. In this work, attenuated total reflectance infrared spectroscopy studies showed that no primary amine groups resulted from this treatment of parylene-C. Instead, reactive nitrogen-bearing radicals from the plasma appear to have been complexed by chlorine in the polymer. The formation of these complexes scavenged nitrogen-bearing radicals from the plasma and prevented the formation of nitrogenous species, such as the desired primary amines, on the parylene-C. These results are consistent with results of ammonia plasma treatment of other chlorinated polymers and suggest that alternative approaches are required to create nitrogen-bearing species on parylene-C.

Mobilisation of heavy metals by deicing salts in a roadside environment

The seasonal variations of some selected heavy metals (Cd, Cu, Pb and Zn) and principal anions in soil solutions were monitored as a function of distance from the road at two field sites in Sweden. During the winter, the conductivity, concentrations of dissolved sodium and chloride increased dramatically due to the application of deicing agents (i.e. NaCl). Due to ion exchange, the pH decreased one unit in the soil solutions, whereas the concentrations of total organic carbon decreased due to coagulation and/or sorption to stationary solids. The heavy metal concentrations increased during the winter, but through different mechanisms. Cadmium concentrations in the aqueous phase increased as a response to ion exchange, possibly also enhanced by the formation of chloride complexes. Similarly, the concentrations of zinc increased, due to ion exchange, with calcium and protons. The mechanisms of mobilisation for copper and lead were not that clear probably due to association with coagulated or sorbed organic matter in combination with colloid dispersion.

Structural Effects and Microheterogeneity in Concentrated Solutions and Their Role in the Formation of Cadmium Chloride Complexes

The proton relaxation rate and Raman spectra in the regions of vibrations of the Cd-Cl, Cd-OH2 groups and bending vibrations eta4 of nitrate ions in the systems CdAn2-NaCl-H2O (An = Cl-, ClO4-, NO3-) were measured. In the range of subeutectic concentrations of cadmium salts all possible forms of chloride complexes of cadmium are formed. In the posteutectic region the formation of complexes is structurally induced; it depends on the nature of dominating cybotactic groups and is limited to the formation of only low-coordinate forms. The mechanisms of the formation of chloride complexes in perchlorate and nitrate systems were proposed. It was concluded that, in contrast to the chloride system, the nitrate and perchlorate systems in the presence of sodium chloride are characterized by structural microheterogeneity. The distinctions in the nature of the microheterogeneity and its effect on the complex formation were considered. The solubility polytherm and Raman spectra of the system Cd(NO3)2-NaCl-H2O with a high content of the both salts were measured. The causes of abnormally high mutual solubility of nitrate salts in multicomponent solutions containing salts that crystallize in the hydrated and anhydrous forms were suggested.

Protonation of polyamines in NaCl aqueous solution and binding of Cl − by polyammonium cations

Equilibrium constants relative to the binding of Cl − by nine open chain polyammonium cations (di, tri and tetra) were determined by potentiometric measurements (H +-glass electrode), at T=25°C. To this end the protonation constants of these amines were measured in NaCl aqueous solutions, in the ionic strength range 0.1< I≤1 mol dm −3. The different amines (some of which are N-alkyl substituted) were chosen in order to consider several factors affecting the values of protonation constants, the chloride complex formation constants and the dependence on ionic strength of apparent protonation constants. As concerns these last two points, it was found that fully N-alkyl substituted amines behave in a very similar way, with respect to partially or non-substituted ones. Simple linear relationships are reported involving chloride formation constants, parameters for the dependence on ionic strength of protonation constants and charges in polyammonium cations. The complexes formed by two linear polyamines with NO 3 − have also been studied for comparison. Literature data are examined.

Coordination chemistry of trivalent lanthanide and actinide ions in dilute and concentrated chloride solutions.

We have used EXAFS spectroscopy to investigate the inner sphere coordination of trivalent lanthanide (Ln) and actinide (An) ions in aqueous solutions as a function of increasing chloride concentration. At low chloride concentration, the hydration numbers and corresponding Ln,An-O bond lengths are as follows: La3+, N = 9.2, R = 2.54 A; Ce3+, N = 9.3, R = 2.52 A; Nd3+, N = 9.5, R = 2.49 A; Eu3+, N = 9.3, R = 2.43 A; Yb3+, N = 8.7, R = 2.32 A; Y3+, N = 9.7, R = 2.36 A; Am3+, N = 10.3, R = 2.48 A; Cm3+, N = 10.2, R = 2.45 A. In ca. 14 M LiCl, the early Ln3+ ions (La, Ce, Nd, and Eu) show inner sphere Cl- complexation along with a loss of H2O. The average chloride coordination numbers and Ln-Cl bond lengths are as follows: La3+, N = 2.1, R = 2.92 A; Ce3+, N = 1.8, R = 2.89 A; Nd3+, N = 1.9, R = 2.85 A; Eu3+, N = 1.1, R = 2.81 A. The extent of Cl- ion complexation decreases going across the Ln3+ series to the point where Yb3+ shows no Cl- complexation and no loss of coordinated water molecules. The actinide ions, Am3+ and Cm3+, show the same structural effects as the early Ln3+ ions, i.e., Cl- ion replacement of the H2O at high chloride thermodynamic activities. The Clion coordination numbers and An-Cl bond lengths are: Am3+, N = 1.8, R = 2.81 A; Cm3+, N = 2.4, R = 2.76 A. When combined with results reported previously for Pu3+ which showed no significant chloride complexation in 12 M LiCl, these results suggest that the extent of chloride complexation is increasing across the An3+ series. The origin of the differences in chloride complex formation between the Ln3+ and An3+ ions and the relevance to earlier work is discussed.

Thermodynamics of aqueous gallium chloride: Activity coefficients in dilute and high chloride solutions with consideration of the effects of hydrolysis and chloride complex formation

An attempt is made to evaluate the Pitzer parameters for activity and osmotic coefficients in aqueous GaCl 3 solutions on the basis of literature data. Anion exchange data demonstrate the necessity of incorporating the formation of the GaCl − 4 complex and allow estimation of the following parameters at 25°C: β 0 (GaCl 3) = 0.3761 kg mol −1; β 1 (GaCl 3) = 15.72 kg mol −1; C(GaCl 3) = −0.0034 kg 2 mol −2; log K 4 = −8.28 for the reaction Ga 3+ + 4Cl − ⇌ GaCl 4 −; β 0 (HGaCl 4) = 0.0641 kg mol −1; β 1 (HGaCl 4) = 0.2945 kg mol −1; C (HGaCl 4) = 0.0004 kg 2 mol −2. The latter β 1 and C parameters are taken equal to those of HCl. These results indicate that at 25°C GaCl 4 − complex formation in nearly pure GaCl 3 solutions becomes important only above concentrations of about 4 mol kg −1 GaCl 3. In solutions with low Ga/Cl ratio's, complexation is dominant above chloride concentrations of about 8 mol kg −1. With increase in temperature complexation extends to lower concentrations. Renewed evaluation of potentiometric data confirms that the NBS-value of −159 kJ mol −1 for the standard Gibbs free energy of formation of aqueous Ga 3+ is a reasonable estimate.