Polyurethane foam for the extraction of rhodium and its separation from iridium

The rate of reaction of rhodium with thiocyanate at 90 degrees in the presence of lithium chloride or sufficient hydrochloric acid and the subsequent extraction of the metal from hydrochloric acid medium by polyether-type polyurethane foam was investigated. The effect of the chloride salts of different cations decreased in the order Li(+) > Na(+) > K(+) indicating that Rh(SCN)(6)(3-) is extracted through a simple solvent-extraction mechanism rather than the "cation-chelation" mechanism. The separation of rhodium and iridium was also examined and the results indicated that in the presence of 5-fold excess of iridium, an average of 95 +/- 2% iridium remained in the aqueous phase while an average of 93 +/- 2% rhodium was retained by the foam.     

Extraction of ruthenium thiocyanate and its separation from rhodium by polyurethane foam

Conditions for the formation and extraction of the thiocyanate complex of ruthenium are reported. Distribution coefficients of more than 10(4) and a capacity of about 0.24 mole per kg of foam were obtained. The effect of the chloride salts of various univalent cations on the extraction of Ru(SCN)(6)(3-) indicated that the efficiency of ruthenium extraction depends on how well the cation fits into the polyether segment of the polyurethane foam, which agrees with the "cation-chelation" mechanism. The separation of ruthenium and rhodium indicated that more than 95% of the rhodium remained in the aqueous phase and about 95% of the ruthenium was retained by the polyurethane foam and could be easily recovered.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)₄ ^2– and the cationic potassium complex of dicyclohexyl-18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)4(2-) and the cationic potassium complex of dicyclohexyl- 18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.     

Extraction of palladium with tri-isobutylphosphine sulphide (cyanex 471) in toluene from chloride solutions containing thiocyanate

The extraction of PD(II) by tri-isobutylphosphine sulphide, TIBPS (Cyanex 47 1x), in toluene from aqueous chloride solutions (containing small amounts of thiocyanate) has been investigated. The extraction is enhanced by the presence of thiocyanate, owing to formation of mixed-ligand Pd(II)-Cl(-)-SCN(-)-TIBPS complexes. Analysis of the metal distribution suggests the formation of PdCl(SCN).TIBPS, PdCl(SCN).2TIBPS, Pd(SCN)(2).TIBPS and Pd(SCN)(2).2TIBPS in the organic phase. The equilibrium constants are logK(111) =9.56, logK(112) =12.70, logK(121) =14.73 and logK(122) =17.17, respectively. The ultraviolet absorption spectra of the organic phase support the hypothesis of formation of mixed-ligand complexes.     

Sorption and permeation behaviour of metal thiocyanate complexes on cellulose acetate polymers

Various metal thiocyanate complexes in aqueous solution were sorbed on solid cellulose acetate polymers. The sorption selectivity increased in the order Zn(2+) > Fe(3+) > Cu(2+) > Co(2+) > Ni(2+). The sorption behaviour followed a Langmuir-type adsorption isotherm, and the maximum adsorption capacity was 6.1 x 10(-5) mole of complex per g of polymer under optimum conditions. The zinc species sorbed appear to be NH(4)Zn(H(2)O)(SCN)(3) or (NH(4))(2)Zn(SCN)(4) according to analysis of the sorption equilibrium. The ion-association species formed by the complex zinc anion and the ammonium ion was supposed to be sorbed (or "extracted") onto the polymer matrix. As an application of sorption of metal complexes, a new hyperfiltration process was proposed for selective separation of metal ions. Thus, a mixture of metal thiocyanate complexes was hyperfiltered through cellulose acetate membranes. Permeation of certain metal complexes was preferred, and the selectivity was found to be similar to the sorption selectivity. These findings lead to a generalized idea that hyperfiltration separation of ionic species, particularly anionic metal complexes, can be attained by using polymer membranes which selectively adsorb or extract such ionic species as ion-association complexes onto the polymer matrix.     

Pressure-induced enhancements of luminescence intensities and lifetimes correlated with emitting-state distortions for thiocyanate and selenocyanate complexes of platinum(II) and palladium(II)

The luminescence properties of thiocyanate and selenocyanate platinum(II) and palladium(II) complexes show strong variations with temperature and pressure. The d-d luminescence band maxima for [Pt(SCN)(4)](PPh(4))(2) (1), [Pt(SCN)(4)](n-Bu(4)N)(2) (2), and [Pt(SeCN)(4)](n-Bu(4)N)(2) (4) complexes are centered at ca. 14500 cm(-1) whereas those of the [Pd(SCN)(4)](n-Bu(4)N)(2) (3) and [Pd(SeCN)(4)](n-Bu(4)N)(2) (5) complexes are approximately 2000 cm(-1) lower in energy. Low-temperature luminescence spectra from single-crystal samples have broad bands with highly resolved vibronic structure indicating large displacements of the emitting-state potential energy minimum along several metal-ligand normal coordinates. The largest displacements involve the totally symmetric (a(1g)) stretching modes with frequencies of 295 cm(-1) (1), 303 cm(-1) (2), 274 cm(-1) (3), 195 cm(-1) (4), and 185 cm(-1) (5). The lower frequencies of these dominant progression-forming modes for the selenocyanate complexes lead to luminescence bands that are narrower by ca. 500 cm(-1) (fwhm) than those observed from the thiocyanate complexes. Under external pressures, the room-temperature luminescence intensities and lifetimes show considerable enhancement at pressures up to 40 kbar. This effect is largest for the palladium(II) complexes with lifetimes increasing from approximately 350 ns at ambient pressure up to 62 micros at 30 kbar, an increase by more than 2 orders of magnitude. The platinum(II) complexes exhibit a significant, but noticeably lesser increase of luminescence lifetimes and intensities with increasing pressure. The temperature- and pressure-dependent luminescence decay behavior is rationalized using the emitting-state molecular geometry determined from the resolved low-temperature luminescence spectra combined with the strong-coupling limit of radiationless decay theory.     

Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate

A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +/- 0.03 x 10(4) 1.mole(-1).cm(-1) (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)(3)](2)L and NbO(SCN)(3)L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl(2)(SCN)(3)][(LK)(2)] seems to be the main species formed in the organic phase.     

Molecular tectonics: design and generation of charge-assisted, H-bonded, hybrid molecular networks based on amidinium cations and thio- or isothio-cyanatometallates

Upon combining the bis-amidinium dication 1-2H(+) with thiocyanatometallate M(SCN)(4)(2-) (M = Pd, Hg) or isothiocyanatometallate Cu(NCS)(4)(2-) anions (behaving as H-bond donor and acceptors, respectively) three new hybrid molecular networks have been obtained in the crystalline phase and structurally characterized by X-ray diffraction on single crystals. Whereas for the combination of tecton 1-2H(+) and both Pd(SCN)(4)(2-) and Hg(SCN)(4)(2-) anions analogous 1-D H-bonded networks were observed, for the Cu(NCS)(4)(2-) anion a 2-D network was obtained. Based on structural features of both components, the formation of the two types of networks is discussed.     

Ion Exchange Separation of Platinum and Palladium by Nucleophilic Displacement With Thiocyanate or Thiourea1,2

The separation of platinum and palladium, by adsorption onto weak base anion exchange resins, Amberlite XE 299, or ionex (derived from Amberlite XE-305) from 1M hydrochloric acid, followed by ligand substitution with sulfur nucleophiles is described.

In the thiourea system, cationic thiourea complexes are produced, which cannot be readsorbed into the resin. In the thiocyanate system the formation of Pd(SCN)₄ ^2- is favored in both solution and polymer phases. The Pd(SCN)₄ ^2-. readsorption into the anion exchange resin is the basis for the separation of platinum from palladium.     

Polyurethane foam extraction of platinum-tin halide complexes

The sorptive capacity of the polyether-based foam was determined to be between 0.85 and 0.92 moles/kg for the platinum-tin(II) chloride complex. At hydrochloric and hydrobromic acid concentrations up to 3.0M, the platinum-tin(II) bromide complex had higher extraction efficiencies than the platinum-tin(II) chloride complex. Sorptions were optimized at 5.0M hydrochloric acid and 3.0M hydrobromic acid and distribution ratios as high as 2.0 x 10(5) 1./kg were observed at high foam:platinum ratios. The percent of platinum extracted increased when the alkali metal cations are added in the order K(+) < Na(+) < Li(+) for polyether foam, and decreased in the order K(+) > Na(+) > Li(+) for polyester foam. Also, the sorption efficiencies increased as the proportion of poly(ethylene oxide) of the foam was increased. A Scatchard plot analysis shows that there is a 2:1 ratio of loosely bound platinum to tightly bound platinum with the polyether foam, however, the experimental results are consistent with a weak-base anion exchange mechanism as the prominent method of sorption. For polyester foam, results are consistent with a solvent-like ion-pair sorption mechanism.     

Kinetics and mechanism of back-extraction: selected palladium extraction systems

The equilibrium and kinetics of back-extraction (stripping) of palladium originally extracted as PdCl^2?₄ from the chloroform extracts obtained with 1-(2-pyridylazo)-2-naphthol (PAN), 7-(4-ethyl-1-methyloctyl)quinolin-8-ol (Kelex 100) or dioctyl sulfide (R₂S) were investigated. Replacement of chloride in extracted species by thiocyanate occurs prior to back-extraction. The back-extraction equilibria have been described by Pd(SCN)₂(R₂S)₂(o) + 2SCN^?K_BX1 Pd(SCN)^2?₄ + 2R₂S(o), with K_BX1=10^{?(1.16±0.05)}, and Pd(SCN)PAN(o) + 3SCN^? + H⁺K_BX2 Pd(SCN)^2?₄ + PAN(o), with K_BX2=10^4.89±0.06. The rate of stripping from PdPAN and PdKelex 100 displayed an inverse first-order dependence on the solution pH, a second-order dependence on the thiocyanate concentration and was zero order in both the chloride and the organic phase chelate concentration. More complicated kinetics were observed for palladium stripping in the dioctyl sulfide system. In all systems, the enhancement in stripping rate parallels the size of the “trans effect”.     

Reactions of carbon monoxide with free palladium oxide clusters: strongly size dependent competition between adsorption and combustion

The gas phase reactions of carbon monoxide with small mass-selected clusters of palladium, Pd(x)(+) (x = 2-7), and their oxides, Pd(x)O(+) (x = 2-7) and Pd(x)O(2)(+) (x = 4-6), have been investigated in a radio frequency ion trap operated under multi-collision conditions. The bare palladium clusters were found to readily adsorb CO yielding a highly size dependent product pattern. Most interestingly, the reactions of the pre-oxidized palladium clusters with CO lead to very similar product distributions of Pd(x)(CO)(z)(+) complexes as in the case of the corresponding pure Pd(x)(+) clusters. Consequently, it has been concluded that the investigated palladium oxide clusters efficiently oxidize CO under formation of the bare clusters, which further adsorb CO molecules yielding the previously observed Pd(x)(CO)(z)(+) product complex distributions. This CO combustion reaction has been observed even at temperatures as low as 100 K. However, for Pd(2)O(+), Pd(6)O(+), Pd(6)O(2)(+), and Pd(7)O(+) a competing reaction channel yielding palladium oxide carbonyls Pd(x)O(CO)(z)(+) could be detected. The latter adsorption reaction may even hamper the CO combustion under certain reaction conditions and indicates enhanced activation barriers involved in the CO oxidation and/or the CO(2) elimination process on these clusters.     

Solvent extraction of Tm(III) by sulfoxides and mixtures of DPSO (di-N-pentyl sulfoxide) and HTTA (thenoyl-trifluoroacetone) from perchlorate and thiocyanate media

Extraction of Tm(III), from thiocyanate media, by different sulfoxides (R₂SO) has revealed that the extractable complex is Tm(SCN)₃·4 R₂SO. When mixtures of DPSO and HTTA are used for the extraction of Tm(III) from thiocyanate or perchlorate media, synergistic enhancement of the extraction of Tm(III) results. The complexes responsible for the enhanced extraction are Tm(TTA)₃·DPSO and Tm(TTA)₃·2 DPSO when perchlorate media were employed for the extraction and Tm(SCN)(TTA)₂·2 DPSO and Tm(SCN)₂(TTA)·3 DPSO, in addition to the above two when a thiocyanate medium was employed for the extraction. Values of equilibrium constants for some equilibria encountered in the extraction of Am(III) and Tm(III) by mixtures of DPSO and HTTA are given.     

Highly specific spectrophotometric method for palladium(II) determination with 3-(5'-tetrazolylazo)-2,6-Diaminotoluene in the presence of chlorides. Kinetic and equilibrium study of reactions

3-(5'-tetrazolylazo)-2,6-Diaminotoluene (TEADAT, H(3)L(2+)) forms stable 1:1 and 1:2 (metal:ligand) pink-red complexes (lambda(max) 506 and 536 nm) with palladium(II). The apparent molar absorptivity of 1:2 complex is 5.2 x 10(4) 1.mol(-1). cm(-1) at 536 nm. Equilibrium constants beta*(nl) for reactions PdCl(2-)(4) + nH(3)L(2+) right harpoon over left harpoonright harpoon over left harpoon PdCl(4-n) (H(2)L)(2n-2)(n) + n Cl(-) + n H(+) were determined: logbeta*(1) = 4.09 +/- 0.05, logbeta*(2) = 8.40 +/- 0.02, corresponding stability conditional constants of PdCl(3)(H(2)L) and PdCl(2)(H(2)L)(2+)(2) were log beta(1) = 19.03, log beta(2) = 26.74. The formation of complexes was rather slow but could be speeded up considerably by the catalytic effect of trace amounts of thiocyanate. Constant absorbance values were thus reached in 2-5 min. A rapid, sensitive and highly specific method for the determination of palladium(II) at pH 1.42 in 0.25M NACl has been worked out with a detection limit of 0.54 mug. Interference of precious and common metal ions have been studied and the method has been applied for the determination of palladium in Pd asbestos, oakay alloys and various catalysts and for the determination of palladium in precious metals.     

Extraction of palladium thiocyanate with polyurethane foam

Conditions for the extraction of the thiocyanate complex of palladium by polyether-type polyurethane foam are reported. Distribution ratios of more than 10(6) with a capacity of about 0.8 mole per kg of foam were obtained. The palladium could be rapidly recovered from the foam with high efficiency by use of ammonia solution. The efficiency of palladium extraction depends on how well the cation associated with the complex fits into the polyether segment of the polyurethane foam.     

Mechanism of palladium-catalyzed diene cyclization/hydrosilylation: direct observation of intramolecular carbometalation

The results of kinetic, deuterium-labeling, and low-temperature NMR studies have established a mechanism for the palladium-catalyzed cyclization/hydrosilylation of dimethyl diallylmalonate (1) with triethylsilane involving rapid, irreversible conversion of the palladium silyl complex [(phen)Pd(SiEt(3))(NCAr)](+) [BAr(4)](-) [Ar = 3,5-C(6)H(3)(CF(3))(2)] (4b) and 1 to the palladium 5-hexenyl chelate complex [(phen)Pd[eta(1),eta(2)-CH(CH(2)SiEt(3))CH(2)C(CO(2)Me)(2)CH(2)CH=CH(2)]](+) [BAr(4)](-) (5), followed by intramolecular carbometalation of 5 to form the palladium cyclopentylmethyl complex trans-[(phen)Pd[CH2CHCH2C(CO2Me)2CH2CHCH2SiEt3](NCAr)]+ [BAr4]- (6), and associative silylation of 6 to release 3 and regenerate 4b.     

Extraction of mercury(II) from aqueous thiocyanate solutions with 5-(4-pyridyl)nonane in benzene, and its subsequent atomic-absorption spectrometric determination

Tracer ( approximately 10(-8)M) mercury(II) can be quantitatively extracted with 5-(4-pyridyl)nonane in benzene from aqueous thiocyanate solutions that are up to 6M in HCl, 1M in H(2)SO(4) or 0.25M in HNO(3), in a single extraction. Optimal conditions for the extraction are given, based on a critical study of the relevant factors such as the effects of the acids, thiocyanate, salting-out and complexing agents and the reagent concentration. The mechanism underlying these extractions is discussed on the basis of the results obtained from partition and slope-analysis data. The extraction of the metal as Hg(PyN)(2)(SCN)(2) is indicated. The extracted mercury can be stripped from the non-aqueous layer with various aqueous solutions, including nitric acid (2M), sodium citrate ( 1M) and sodium thiosulphate (0.1 M). Common salts do not depress the extraction. Distribution coefficients and separation factors of several elements relative to mercury(II) are reported for media that contain the optimal concentrations of the mineral acids and are in 0.2M in potassium thiocyanate. The data have been applied for the determination of mercury in soil and water samples by atomic-absorption spectrometry.     

Synthesis and structure of new dinuclear palladium complex containing no bridging ligands

Oxidation of the mononuclear semiquinonediimine complex [(NPh)(NH)C₆H₄]₂Pd with silver trifluoromethanesulfonate afforded the diamagnetic dinuclear dicationic palladium complex {[(NPh)(NH)C₆H₄]₂Pd}₂(O₃SCF₃)₂ with a Pd...Pd distance of 3.267(1) . The complex was structurally characterized, and its spectroscopic and electrochemical properties were studied.     

The cation-chelation mechanism of metal-ion sorption by polyurethanes

The mechanism of sorption of ions by polyurethanes has been investigated through detailed studies of the extraction of cobalt(II) thiocyanate and the salts of several organic acids. Polyether-based polyurethanes. particularly those containing poly(ethylene oxide), were found to be distinctly superior to polyesters in the sorption of salts and performed much better than might be expected by analogy with monomeric liquid solvents. The results were judged to be inconsistent with several possible mechanisms, including adsorption, solvent extraction, weak or strong base anion-exchange, and complexation of metal anions by the polymer. A new proposal, termed the cation chelation mechanism (CCM), was advanced to account for the observations. In this view, a number of cations (including those of the alkali metals, alkaline earth metals, some transition metals, NH(+)(4), RNH(+)(3) and perhaps H(3)O(+)) may be multiply complexed (chelated) by portions of the polymer, thus facilitating the sorption of accompanying anions. As predicted by the mechanism, moderately strong and selective complexation of several cations was observed to occur with the following order of selectivity: Li(+) < Na(+) < Cs(+) < Rb(+) < K(+) approximately NH(+)(4) < Ag(+) approximately Tl(+) < Ba(2+) < Hg(2+) < Pb(2+). Such behaviour parallels that known for many crown and non-cyclic polyethers and is therefore identified with the polyether portions of the polymer, which are thought to adopt helical conformations surrounding the complexed cations. The cation-chelation mechanism may be widely applicable to the sorption of ions of several types by polyether-based polyurethanes, particularly when large, hydrophobic anions (such as anionic metal complexes) are accompanied by an excess of chelatable cations.