Platinum Chloro Complexes Research Articles

11 Platinum Speciation in Air Samples

Abstract The health effects of chloroplatinates are generally well recognised and acknowledged by regulators in both EU and USA (Platinum salt sensitivity). But what about Platinum species? Speciation is essential for valid toxicology assessments and speciation studies are lacking in this respect – it’s known that certain Platinum chloro complexes are more sensitising than others. A method for the separation of platinum chloro-complexes and their hydrolysis products has been developed. The different platinum chemical species are separated into their charged compounds in 0.07 M HCl: [PtCl4]2-, [PtCl6]2-, [PtCl3(H2O)]-, [PtCl5(H2O)]- and a zero charged/ bis-aquo compound. The separation was carried via an ion exchange chromatographic column coupled to a quadrupole ICP-MS for the detection of the different anionic platinum chloro-species. A gradient program consisting of a mixture of HCl and HClO4 was used as eluent to ensure the separation of the species. A process has been developed for the analysis of platinum species extracted from air filters in a PGM facility with JM. Although the methodology for speciation is robust, further work needs to be carried out in terms of alternative sample collection to the air filters such as bubblers as the process of sonication, drying and acid contact on the filters does adversely affect the chemical species in solution. A comparison between Platinum speciation in air filters collected form IOM samplers and bubblers will be included in this presentation. This work will generate data to help characterise different workplaces based on the types of task-based exposure.

Autoclave dissolution of platinum metals in hydrochloric acid oxidizing media

The paper provides the results obtained in the study of the features of metallic platinum, rhodium and iridium dissolution in hydrochloric acid solutions under hydrothermal autoclave conditions. Hydrogen peroxide was used as an oxidizing agent. Solid and liquid phases were brought into contact after reaching a predetermined temperature, which is critically important in the study of rhodium black and platinum plate dissolution kinetics due to the high rates of these processes. The concentrations of metals in solutions were determined by atomic absorption spectroscopy and inductively coupled plasma mass spectrometry. The forms of rhodium, iridium, and platinum chlorocomplexes in solutions were determined using the spectrophotometric method. As a result of the experiments, the conditions of platinum plate and rhodium quantitative dissolution (in the form of affined powder and a plate) were determined and it was shown that at 210 °C in 6M hydrochloric acid as a medium with the addition of 5 vol.% hydrogen peroxide, iridium taken in the form of affined powder went into the solution by 50 % within more than 50 h, while the platinum plate dissolved completely at 130 °C in about 120 min. Kinetic data analysis using the shrinking core model showed that rhodium black and affined rhodium and iridium powders dissolve under autoclave conditions in a kinetic mode. The results obtained can be used both in analytical chemistry for the quantitative determination of inert platinum metals and in refining production to improve the technology for processing raw materials containing platinum group metals (PGMs) and to optimize approaches to the synthesis of pure chlorocomplex compounds of PGMs.

Use of platinum carbonyl complexes in the synthesis of Pt/MgAlO x catalysts

Pt/MgAlO x samples have been obtained by the adsorption of platinum carbonyl complexes on aluminum-magnesium oxides with Mg: Al = 2, 3, and 4. The composition of the adsorbed complexes has been determined. The catalysts synthesized from the carbonyl precursor show a higher activity in propane dehydrogenation and are less prone to deactivation than the catalysts prepared using platinum chloro complexes.

Formation of Pt/C catalysts on various carbon supports

Platinum catalysts with the active component content of 5–40 wt % on various carbon supports have been synthesized by the reductive hydrolysis of platinum chloro complexes. The degree of dispersion of the supported platinum decreases with an increasing weight percentage of the metal in the catalyst. The following mechanism of Pt/C catalyst formation is deduced from experimental data: H2PtCl6 adsorption on the support surface generates platinum nuclei, which then grow owing to the deposition of platinum ions under the action of an alkali and a reductant.

Competitive ligation between carbon monoxide and propiononitrile in chloro-complexes of platinum(II)

EtCN partially displaces coordinated carbon monoxide from cis-PtCl 2(CO) 2 giving an equilibrium mixture of the two geometrical isomers of PtCl 2(CO)(NCEt), together with unreacted cis-PtCl 2(CO) 2, as monitored by IR and NMR measurements. The equilibrium has also been studied starting from PtCl 2(NCEt) 2, through displacement of coordinated EtCN by CO. The equilibrium constant of the reaction between PtCl 2(CO)(NCEt) [ cis + trans] and CO to produce cis-PtCl 2(CO) 2 (48 ± 6, corresponding to Δ G 0 = −9.5 ± 0.3 kJ mol −1) has been measured at 23.4 °C, in the presence of SnCl 2 as catalyst, the uncatalysed reaction being exceedingly slow. With an appropriate control of the CO partial pressure, PtCl 2(CO)(NCEt) was obtained in a nearly quantitative yield either from cis-PtCl 2(CO) 2 + EtCN or from PtCl 2(NCEt) 2 + CO. The molecular and crystal structure of cis-PtCl 2(CO)(NCEt) has been solved by X-ray diffractometry.

A Kinetic Study of the Competition between Carbon Monoxide and Alkenes in Chloro Complexes of Platinum(II)

Alkenes (cyclohexene; 1-octene) react with cis-PtCl2(CO)2, leading to cis-PtCl2(CO)(alkene) (1a, alkene = cyclohexene; 1b, alkene = 1-octene). The substitution kinetics to 1a and 1b in 1,2-dichloroethane in the temperature range 273−308 K have the following second-order rate constants at 298 K, respectively: cyclohexene, (0.94 ± 0.07) × 10-3 M-1 s-1; 1-octene, (2.33 ± 0.05) × 10-2 M-1 s-1. The activation parameters are ΔH* = 37 ± 4 kJ mol-1, ΔS* = −180 ± 10 J K-1 mol-1 for the reaction affording 1a and ΔH* = 36.5 ± 0.7 kJ mol-1, ΔS* = −154 ± 2 J K-1 mol-1 for the reaction to 1b. The large negative values of the activation entropies are consistent with an associative mechanism. The reverse reactions proceed with a similar rate constant.

Competition between Carbon Monoxide and Alkenes in Chloro Complexes of Platinum(II)

Alkenes (cyclohexene; 1-octene) and dienes (cyclooctadiene, COD; norbornadiene, NBD) react with cis-PtCl2(CO)2, leading, respectively, to partial and complete displacement of coordinated carbon monoxide. Equilibrium constants at 21 °C in 1,2-dichloroethane are (2.4 ± 0.5) × 10-3 and (2.8 ± 0.4) × 10-2 for cyclohexene and 1-octene, respectively. Thermodynamic data correspond to ΔH° (kJ mol-) and ΔS° (J mol-1 K-1) = 30 ± 4 and 51 ± 15 for cyclohexene and 36 ± 2 and 95 ± 8 for 1-octene.

Structural investigations of palladium(II) and platinum(II) complexes of salicylhydroxamic acid.

Complexes of salicylhydroxamic acid (shaH) with palladium(II) and platinum(II) were investigated. The synthesis of [Pt(sha)(2)] was attempted via a number of methods, and ultimately (1)H NMR investigations revealed that salicylhydroxamate would not coordinate to chloro complexes of platinum(II). However, [Pt(sha-H)(PPh(3))(2)] was successfully synthesized and the crystal structure determined (orthorhombic, space group Pca2(1) a = 17.9325(19) A, b = 11.3102(12) A, c = 18.2829(19) A, Z = 4, R = 0.0224). The sha binds via an [O,O] binding mode, in its hydroximate form. In contrast the palladium complex [Pd(sha)(2)] was readily synthesized and crystallized as [Pd(sha)(2)](DMF)(4) in the triclinic space group P(-)1,a = 7.066(1) A, b = 9.842(2) A, c = 12.385(2) A, alpha = 99.213(3)(o), beta = 90.669(3), gamma = 109.767(3)(o), Z = 1, R = 0.037. The unexpected [N,O'] binding mode of the salicylhydroxamate ligand in [Pd(sha)(2)] prompted investigation of the stability of a number of binding modes of salicylhydroxamic acid in [M(sha)(2)] (M = Pd, Pt) by density functional theory, using the B3LYP hybrid functional at the 6-311G* level of theory. Geometry optimizations were carried out for various binding modes of the ligands and their relative energies established. It was found that the [N,O'] mode gave the more stable complex, in accord with experimental observations. Stabilization of hydroxamate binding to platinum is evidently afforded by soft ligands lying trans to them.

Speciation of platinum–chloro complexes and their hydrolysis products by ion chromatography: Determination of platinum oxidation states

A method for the separation and determination of tetrachloroplatinate, PtCl42−, and hexachloroplatinate, PtCl62−, applying UV absorption detection was developed and statistically validated. Independent and specific Pt quantification was possible by off-line inductively coupled plasma mass spectrometric determination. Special attention was paid to storage and stability of species standards and their suitability for calibration. The species purity of standard solutions was determined and the hydrolysis kinetics were investigated. Qualitatively, a number of Pt(II) and Pt(IV) complexes formed by hydrolysis from tetra- and hexachloroplatinate were detected. First applications of the methods are described.

The role of matrix effects on selectivity in ion exchange resins

Selectivity in an ion exchange resin need not be determined by the nature of the active group alone. There may be a substantial contribution from the matrix with an observed increase in the separation factor between platinum chloro-complexes and the Cl − ion by a factor of up to 15. Matrix effects are dealt with for resins containing the isothiouronium group in one case and the pyridyl-imidazole group in another. Possible loading mechanisms for the platinum-chlorocomplex on isothiouronium resins, and copper and iron (III) on pyridyl-imidazole resins are considered.

The separation of platinum and iridium by ion flotation

The anionic chlorocomplexes of platinum(IV) and iridium(III) are separated by ion flotation from acidic, aqueous solutions with cationic surfactants of the type C 16H 33NR' 3Br, where R' is methyl, ethyl, n-propyl, or n-butyl. The PtCl 6 2-, which forms readily floatable salts with each of the surfactants, is selectively floated from the IrCl 6 3- and recovered after flotation in n-butyl acetate. The efficiency of the separation increases as the R' chain length increases and a quantitative separation is obtained with hexadecyltributyl-ammonium bromide (HTBAB) in 0.1 M HCl solutions. Since the flotation properties of Ir(IV) are similar to those of Pt(IV), hydroxylamine hydrochloride is used to reduce Ir(IV) to Ir(in) selectively in the presence of Pt(IV).

Reactions of the tertiary phosphines R 2P [formula omitted]F 2) n with group VI hexacarbonyls and salts of platinum and palladium

The tertiary phosphines R 2P CCCl(C F 2) n (R = C 6H 5 or C 6H 11; n = 2,3, or 4) react with M(CO) 6 (M = Cr, Mo, W) to give R 2P CCCl(C F 2) nM(CO) 5 in which the ligand is bonded to M through P alone. Similar bonding is found in some chloro-complexes of platinum and palladium.

Countercurrent extraction separation of some platinum group metals

Distribution coefficients were determined for the partitioning of the chloro-complexes of platinum, palladium, rhodium, and iridium between tributyl phosphate and various concentrations of hydrochloriic acid. Theoretical calculations based on the experimentally determined distribution coefficients indicated that a seventeen stage countercurrent extraction apparatus would resolve mixtures of platinum and palladium, platinum and rhodium, and rhodium and iridium. Mixtures of platinum and palladium, and platinum and rhodium were resolved in a fashion predicted by theory. Mixtures of rhodium and iridium were not completely resolved.