Ind. Eng. Chem. Res. 2000, 39, 3611-3615
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Peculiarities of K2PdCl4 and K2PtCl4 Complexation with Polymer-Supported Dibenzo-18-crown-6 Galina G. Talanova,*,†,‡ Konstantin B. Yatsimirskii,*,‡ and Olga V. Kravchenko‡ Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, and L. V. Pisarzhevskii Institute of Physical Chemistry, NAS of Ukraine, Prospect Nauki 31, 252028 Kiev-28, Ukraine
Dibenzo-18-crown-6 supported on a styrene-divinylbenzene copolymer matrix (PDB18C6) was found to be an efficient sorbent of Pd(II) and Pt(II) from aqueous K2PdCl4 and K2PtCl4 solutions, respectively, because of formation of complex ion pairs where K+ was coordinated with the crown ether moiety while the platinides(II) were present in the paired anionic species. Sorption stoichiometry and binding constants determined for the interaction of PDB18C6 with K2PdCl4 and K2PtCl4 were distinctive. On the basis of spectral characteristics (electronic absorption and IR) obtained for the immobilized complexes, Pt(II) was assumed to be sorbed as anion [PtCl4]2while Pd(II) formed multinuclear species [PdnCl2n+2]2-. Within the complex ion pairs, Pd(II), in contrast with Pt(II), may interact with the aromatic substituents of the immobilized DB18C6. Introduction Macrocyclic polyethers (crown ethers) are known for forming stable complexes1 with alkali metal cations which allows one to utilize such ligands in metal separations. In particular, crown ethers (CEs) immobilized in organic and inorganic polymeric matrixes have been applied widely as selective alkali metal ion sorbents.2 The complexing ability of CEs for metal ions in sorption2,3 and other interphase separation processes (e. g., solvent extraction4a and membrane transport4b) may vary with the anion identity. Unlike binding of hard alkali metal cations, complexation with soft platinide ions, in particular, Pd2+ and Pt2+, is atypical for CEs containing only hard oxygen donor atoms. Information about sorption of these metal ions by polymer-supported CEs is lacking, to the best of our knowledge.5 However, Pd(II) and Pt(II) are known to form stable chloride-containing anions, the simplest of which are [PdCl4]2- and [PtCl4]2-. Such anions are capable of forming ion pairs with complex cation, [CEalkali metal ion]+. Therefore, interaction of an alkali metal tetrachloropalladate(II) or tetrachloroplatinite(II) with an immobilized ionophore that proceeds via the alkali metal cation coordination by the CE moiety may be accompanied by sorption of the platinide-containing anion. Our preliminary studies6,7 have shown that this approach may be utilized for Pd(II) and Pt(II) separations with polymer-supported CEs. We now report a detailed characterization of K2PdCl4 and K2PtCl4 sorption by the polymer-immobilized dibenzo-18-crown-6 (PDB18C6; see Figure 1). To reveal the peculiarities of Pd(II) and Pt(II) separations by PDB18C6, the composition, binding constants, and spectra of the immobilized complexes were investigated. Experimental Section General Methods and Instrumentation. Diffuse reflectance spectra, R ) f(λ), of the solid polymer * To whom correspondence should be addressed. † Texas Tech University. Fax: (806) 742-1289. E-mail:
[email protected]. ‡ L. V. Pisarzhevskii Institute of Physical Chemistry. Fax: (380-44) 265-6216.
Figure 1. Polymer-supported dibenzo-18-crown-6 (PDB18C6).
samples were recorded in air in the region of 40 00012 000 cm-1 with a Specord M40 spectrophotometer (Zeiss) equipped with an accessory PU7908/24 integration spheroid (MgO was used as a standard). The diffuse reflectance spectra were transformed into absorption spectra, A ) f(λ), by the formula A (%) ) 100% - R (%). The latter integral spectra were disintegrated into the differential components using Microcal Origin (version 4.10). IR spectra (KBr) were measured with a Specord 75IR spectrometer (Zeiss). Spectra in the far-IR region were recorded with a PYE UNIKAM spectrometer. Pd(II) and Pt(II) concentrations in aqueous solution after sorption were determined with a Perkin-Elmer 5000 atomic absorption spectrophotometer. Reagents. PDB18C68 (CE concentration 0.79 mmol/ g) obtained from Biolar (Olaine, Latvia) and reagentgrade K2PdCl4 and K2PtCl4 purchased from Strem Chemicals were used without further purification. General Sorption Procedure. A sample of PDB18C6 was added to 5.00 mL of an aqueous K2MCl4 (M ) Pd or Pt) solution containing varied quantities of KCl to avoid hydrolysis. The mixture was shaken for 4.5 h (until equilibrium was reached),6,7 and the sorbent was filtered off. The equilibrium Pd(II) and Pt(II) concentrations in the aqueous phase after sorption were determined by atomic absorption spectrophotometry. The quantity of sorbed Pd(II) and Pt(II) was calculated as the difference between the initial and equilibrium metal concentrations in the aqueous solution. Preparation of the Immobilized Complex Samples for the Spectral Measurements. A sample of PDB18C6 was contacted with the aqueous solution
10.1021/ie0000616 CCC: $19.00 © 2000 American Chemical Society Published on Web 09/13/2000
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of K2MCl4 (M ) Pd or Pt) as described in General Sorption Procedure. The polymer was filtered off, dried in vacuo, and powdered, and the spectra were measured. Results and Discussion Sorption of K2PdCl4 and K2PtCl4 by PDB18C6. In an aqueous solution, K2PdCl4 and K2PtCl4 are known to form a variety of mixed chloro-aqua complexes [MCln(H2O)4-n](2-n), where M is Pd or Pt and n varies from 1 to 4.9 The stability constants of these complexes suggest that all of them may coexist in solution and their fractions vary with the Cl- concentration. Therefore, two different modes of PDB18C6 interaction with K2MCl4 in an aqueous solution may be anticipated. One is the direct coordination of the platinide(II) as the neutral species, [MCl2(H2O)2], or cation, [MCl(H2O)3]+, with oxygen donor atoms of the CE. The other, contrasting mode is the formation of complex ion pairs where Pd(II) and Pt(II) are present as the anions [MCl3(H2O)]and/or [MCl4]2- while K+ is coordinated with the CE oxygens. The first of the suggested mechanisms seems less probable because for soft electron acceptors, i.e., Pd(II) and Pt(II), coordinate bonding with hard oxygen electron donors is atypical. Additionally, to avoid hydrolysis of K2PdCl4 and K2PtCl4 leading to precipitation of the corresponding hydroxides that have limited solubility in water,10 at least 50 mM KCl must be added to the aqueous solution. Under these conditions, the approximate percentages of [PdCl2(H2O)] and [PdCl(H2O)3]+ are 3 and 0.03%, respectively. The content of the analogous Pt(II) species is even smaller because anionic chloro-aqua complexes of Pt(II) are much more stable than those of Pd(II).9 Hence, the interaction of PDB18C6 with neutral and cationic Pd- and Pt-containing species was neglected in this work. The interaction of K2PdCl4 and K2PtCl4 with PDB18C6 was assumed to proceed by the ion-pairing mechanism with participation of the Pd- and Pt-containing anions. This assumption was consistent with the previously reported dependence of Pd(II)6 and Pt(II)7 sorption by PDB18C6 on K+ and Cl- concentrations in aqueous solution. Because both [MCl3(H2O)]- and [MCl4]2- might participate in the ion pair formation, thereby complicating the complex stoichiometry determination, it seemed rational to minimize the number of Pd- and Pt-containing species in the aqueous phase. This was achieved by increasing the concentration of Cl- (KCl) in the aqueous solution to 0.50 M. Under such conditions, more than 91% of Pd(II) and 98.6% of Pt(II) existed in the [MCl4]2form. Therefore, the interaction of PDB18C6 with K2PdCl4 and K2PtCl4 may be described by the following equations:
2K+aq + [MCl4]2-aq + 2Lim ) [(K+L)2(MCl4)2-]im
(1)
and/or
2K+aq + [MCl4]2-aq + Lim ) [(K+L)(MCl4)2-(K+)]im (2) where subscripts aq and im denote aqueous and solid phases, respectively, and Lim is PDB18C6. The immobilized complex ion pairs actually are “ion triads” that consist of two cations and one anion. In fact, (1) and (2) are summary equations that include the cation and
Figure 2. Dependence of K2PdCl4 (b) and K2PtCl4 (O) uptake by PDB18C6 on the relative content of CE units in the sorbent sample, N0CE/N0M (N0Pd ) 20.0 µmol, N0Pt ) 15.9 µmol, and CKCl ) 0.50 M).
anion dehydration steps. The latter are necessary for the salt transfer from the aqueous solutions to the hydrophobic polymer surface. A “blank” polymer containing no CE moieties was applied in the Pd(II) and Pt(II) sorption under otherwise identical conditions to probe for the [MCl4]2- binding due to protonation of the polymer piperazine nitrogens. Because the quantities of sorbed Pd(II) and Pt(II) were insignificant, such an interaction was neglected in this work. Investigation of the CE concentration effect on the binding of K2PdCl4 and K2PtCl4 by PDB18C6 revealed different sorption capacities of the polymeric material for these two platinide salts (Figure 2). Although the percent sorption, aM (%), of both Pd(II) and Pt(II) increased with enhanced ratio N0CE/N0M (where N0CE and N0M are the mole numbers of DB18C6 in the polymer sample and the platinide-containing anion in the aqueous phase), the binding ability of PDB18C6 for Pd(II) was somewhat greater than that for Pt(II) under otherwise identical conditions. The two curves shown in Figure 2 have different parameters, which may result from the unlike compositions of the complexes formed by K2PdCl4 and K2PtCl4 with PDB18C6. Determination of the Complex Composition and Binding Constants. Sorption of K2PdCl4 and K2PtCl4 from aqueous solutions by the polymer-supported DB18C6 may be described by the Langmuir equation:
Q/(1 - Q) ) KCM
(3)
where Q ) aM/a∞, in which aM and a∞ are the current and maximal concentrations, respectively, of the metal ions sorbed by the polymer, CM is the equilibrium concentration of the metal ions in the aqueous phase, and K is the binding constant. Equation 3 may be easily transformed into eq 4. A plot of 1/aM vs 1/CM gives 1/a∞
1/aM ) 1/a∞(1 + 1/KCM)
(4)
as the intercept on the y axis (1/CM f 0 when CM f ∞). Then K is calculated by eq 4. The highest stoichiometry of the immobilized complex may be estimated as a ratio of a∞ and the concentration of the CE moieties in the sorbent. To obtain the adsorption isotherms (see Figure 3a), the initial concentrations of K2PdCl4 and K2PtCl4 in an
Ind. Eng. Chem. Res., Vol. 39, No. 10, 2000 3613 Chart 1
Table 1. Electronic Absorption Spectra of (Bu4N)2PtCl4 and the Complex of K2PtCl4 with PDB18C6 λmax, nm K2PtCl4-PDB18C6
(Bu4N)2PtCl4a,13
525 480 400 351
560 488 397 335 264 230 215
a
Figure 3. Sorption of K2PdCl4 (b) and K2PtCl4 (O) from aqueous solutions containing 0.50 M KCl by PDB18C6 (N0CE ) 40.0 µmol): (a) adsorption isotherms, aM vs CM and (b) plots of 1/aM vs 1/CM.
aqueous 0.50 M KCl solution were varied from 1.60 to 60.0 mM and from 1.20 to 15.0 mM, respectively, while the quantity of DB18C6 in the polymer samples was kept constant (N0CE ) 40.0 µmol). Unlike for Pd(II), when the Pt(II) concentration in the aqueous phase was increased above 15.0 mM, a gray film of the reduced metallic Pt was observed to appear on the PDB18C6 surface and on the walls of the flask as the sorption proceeded. This phenomenon may be explained by the greater oxidizing ability of Pt(II) relative to that of Pd(II): the standard reduction potentials, E° (MCl42-/M0), for Pt(II) and Pd(II) are 0.758 and 0.62 V, respectively.11 The curves in Figure 3a were linearized in the coordinates 1/aM vs 1/CM as shown in Figure 3b, with correlation coefficients r2 of 1.00 for Pt(II) and 0.99 for Pd(II). The a∞ values for K2PdCl4 and K2PtCl4 were found to be 1.61 and 0.66 mmol/g, respectively. The binding constants (K) for these salts calculated by eq 4 were 121 ( 21 and 476 ( 92 L/mol, correspondingly. Therefore, the sorption capacity of PDB18C6 for K2PdCl4 is greater than that for K2PtCl4, although association of the complex cation (K+DB18C6) with [PtCl4]2- is stronger than that with the analogous Pdcontaining anion. For Pt(II) sorption by PDB18C6, the ratio of a∞ and the DB18C6 concentration in the polymer (0.79 mmol/ g) was 0.84. Accordingly, PDB18C6 was assumed capable of binding one [PtCl4]2- ion per each CE moiety, in agreement with eq 2. However, because of the Pt(II) reduction observed when the sorption was attempted from aqueous solutions with C0Pt > 15.0 mM (see vide supra), the maximum Pt(II) binding of only 0.43 mmol/g was achieved.
attribution13 3E g 3A 2g 1A 2g 1E g
πCl-dσ*
Converted from the wavenumbers (cm-1) in ref 13.
In the case of K2PdCl4 sorption by PDB18C6, the ratio of a∞ and the CE concentration in the polymer was 2.04. This suggests that up to two Pd(II) ions per each CE unit may be present in the immobilized complex. Such stoichiometry may not be adequately explained by eqs 1 and 2. A nonstoichiometric binding of Pd(II) by PDB18C6 may be ascribed to the formation of multinuclear, bridged anions [PdnCl2n+2]2- where Cl- ions link together PdCl2 species12a (see Chart 1), which is characteristic for palladium(II) chloride in low-solvating media.12b Competitive Sorption of Pd(II) and Pt(II) by PDB18C6. Competitive sorption of Pd(II) and Pt(II) by the polymer was conducted from the aqueous solution containing equimolar concentrations (4.00 mM) of K2PdCl4 and K2PtCl4 in the presence of 0.50 M KCl. In this experiment, simultaneous binding of both platinides by PDB18C6 was observed. However, the degree of extraction of Pd- and Pt-containing species from an aqueous solution was different. Thus, 48.0% of K2PtCl4 and 32.5% of K2PdCl4 was sorbed. This sequence is in agreement with the larger binding constant of PDB18C6 for Pt(II) relative to that for Pd(II). The actual selectivity of the polymer for Pt(II) over Pd(II) appeared to be lower than the ratio of the corresponding K values, evidently, because of the nonstoichiometric Pd(II) sorption mentioned above. Spectral Characteristics of K2PdCl4 and K2PtCl4 Complexes with the Polymer-Supported DB18C6. (a) Electronic Absorption Spectra. Uncomplexed PDB18C6 showed no absorption in the studied region. However, after sorption of K2PdCl4 and K2PtCl4 from an aqueous solution, the spectrum of the polymer changed dramatically. The positions of the absorption maxima obtained by the spectra disintegration into the differential Gaussian components are given in Tables 1 and 2. For comparison with [DB18C6-K2PtCl4]im, the spectral characteristics of (Bu4N)2PtCl413 are presented in Table 1. Analogously, the spectra of K2PdCl4 and (Bu4N)2Pd2Cl613 are given in Table 2 for comparison with that of the immobilized Pd(II)-containing complex. Absorption spectra of the complexes obtained from K2PdCl4 and K2PtCl4 sorption by PDB18C6 resembled obviously the spectra of planar-square complexes of Pd(II) and Pt(II).13 Thus, [DB18C6-K2PtCl4]im and (Bu4N)2PtCl4 (Table 1) possessed almost identical d f d electron transition bands of 3A2g (forbidden transition) and 1A2g (allowed transition) and showed only slightly different
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Table 2. Electronic Absorption Spectra of K2PdCl4, (Bu4N)2Pd2Cl6, and the Complex of K2PdCl4 with PDB18C6 λmax, nm K2PdCl4PDB18C6
K2PdCl4
(Bu4N)2Pd2Cl6a,13
511 420 344
461 431 346
614 446 397
280
calcd 250
267 245
1A 1E
1g 2g 2g g g
[Cl(t)π-dσ*] uπeu-b1g [Cl(b)π-dσ* LMCT] 1A πb -b 2u 2u 1g 1E
288 238 222 calcd 200 a
3A
1E
327 305
attribution13 3B
588
[Cl(t)σ-dσ* LMCT] 1E σe -b u u 1g [Cl(b)σ-dσ* LMCT]
Converted from the wavenumbers (cm-1) in ref 13.
positions for two other d f d transition bands (3Eg, forbidden transition, and 1Eg, allowed transition). At the same time, in contrast with (Bu4N)2PtCl4, chargetransfer bands (Cl f Pt) that usually are much more intense than those of d f d electron transitions were not observed in the spectrum of [DB18C6-K2PtCl4]im. Probably, these bands were shifted to shorter wavelengths, where they could not be studied with the utilized spectrophotometer. The spectrum of the Pd(II)-containing complex of PDB18C6 (Table 2) was more complicated than that of [DB18C6-K2PtCl4]im. It showed similarities with the spectra of both K2PdCl4 and (Bu4N)2Pd2Cl6 and yet had significant distinctions. In particular, the low-intensity d f d transitions observed for K2PdCl4 and (Bu4N)2Pd2Cl6 in the region of 580-620 nm were absent in the spectrum of the complex of PDB18C6 with K2PdCl4. Positions of four other d f d transition bands of the immobilized complex [DB18C6-K2PdCl4]im varied from those for K2PdCl4 and (Bu4N)2Pd2Cl6. Thus, the bands of [DB18C6-K2PdCl4]im at 305 and 511 nm showed bathochromic shifts relative to the corresponding absorptions of the model salts, while the bands at 344 and 420 nm were observed at slightly shorter wavelength than the analogous d f d transitions of K2PdCl4 and at significantly longer wavelength than the nearest chargetransfer bands of (Bu4N)2Pd2Cl6 (Table 2). Generally, positions and intensities of the absorption bands observed for [DB18C6-K2PdCl4]im in the region of 300520 nm were closer to those of K2PdCl4 than of (Bu4N)2Pd2Cl6. These results suggest that the complex of PDB18C6 with K2PdCl4 contains a variety of anionic species [PdnCl2n+2]2- with a relatively large fraction of [PdCl4]2-. Unlike for [DB18C6-K2PtCl4]im, the absorption band with a calculated maximum of 250 nm was observed in the spectrum of [DB18C6-K2PdCl4]im. This absorption may be attributed to Cl f Pd charge transfer, analogously to the charge-transfer bands of K2PdCl4 and (Bu4N)2Pd2Cl6 observed in the same region. Another possible origin of the absorption at 250 nm may be an interaction of Pd(II) with the immobilized CE or the polymer matrix. (b) Infrared Spectra. The IR spectrum of PDB18C6 (Figure 4a, curve 1) was changed significantly after the sorption of K2PdCl4 (Figure 4a, curve 3). Thus, a series of vibrations in the region of 1000-1200 cm-1 observed for PDB18C6 (as well as for DB18C6), attributed to outof-plane C-H deformation vibrations for 1,2-disubsti-
Figure 4. IR (a) and far-IR (b) spectra of PDB18C6 before (1) and after sorption of K2PtCl4 (2) and K2PdCl4 (3).
tuted benzene rings,14 changed shapes and shifted to lower frequencies by 40 cm-1 upon complexation with K2PdCl4. In addition, a new, low-intensity vibration at 625 cm-1 appeared in the spectrum of complex [DB18C6-K2PdCl4]im (Figure 4b, curve 3). Such a band was not observed in the IR spectrum of the complex obtained from the sorption of KCl by PDB18C6. Therefore, the vibration at 625 cm-1 in the spectrum of [DB18C6-K2PdCl4]im was assumed to be caused by the interaction of the Pd-containing anion with the aromatic substituents of the immobilized DB18C6. Earlier,15 we have reported a biphilic behavior of DB18C6 for alkali metal picrates. The CE was found coordinating the metal cation in the cavity and binding the picrate anion via π stacking with the phenylene groups. The results of the present study suggested that the polymer-supported DB18C6 might exhibit biphilicity for an alkali metal salt with Pd-containing anion as well. In contrast with K2PdCl4, the interaction of K2PtCl4 with PDB18C6 did not induce any obvious changes to the IR spectrum of the polymer-supported ionophore (Figure 4a). This indicates the absence of any direct interaction of Pt(II) with the immobilized DB18C6. In the far-IR region (Figure 4b), K2PtCl4 and K2PdCl4 sorption by PDB18C6 resulted in the appearance of new vibrations at 300 cm-1 for Pt-Cl and at 320 and 295 cm-1 for Pd-Cl (curves 2 and 3, respectively). The frequencies of these bands are characteristic for [PdCl4]2and [PtCl4]2-, correspondingly.16 At the same time, no changes were noted in the region of 400-470 cm-1 where Pd-O and Pt-O vibrations might be observed.16 Therefore, neither Pd(II) nor Pt(II) was coordinated directly to the oxygen donor atoms of the CE. This is consistent with the suggested vide supra mechanism of PDB18C6 interaction with K2PdCl4 and K2PtCl4 via formation of the complex ion pairs where K+ is incapsulated in the CE cavity, while Pd(II) or Pt(II) is present in the associated anion. Conclusions Polymer-supported DB18C6 allows for the efficient separation of Pd(II) and Pt(II) from aqueous chloride
Ind. Eng. Chem. Res., Vol. 39, No. 10, 2000 3615
solutions in the presence of K+ ions. The sorption proceeds via coordination of K+ with the CE oxygen atoms accompanied by the complex cation association with [PtCl4]2- and [PdnCl2n+2]2- anions. Within the complex ion pairs, Pd(II), unlike Pt(II), may interact with the aromatic substituents of the immobilized DB18C6. However, PDB18C6 shows stronger binding of the Pt-containing anions than the Pd-containing species. Acknowledgment This research was supported by the International Soros Science Foundation (Grants UBH000, EPU043006, and PSU063132). Literature Cited (1) Izatt, R. M.; Pawlak, K.; Bradshaw, J. S.; Bruening, R. L. Thermodynamic and Kinetic Data for Macrocycle Interaction with Cations, Anions, and Neutral Molecules. Chem. Rev. 1995, 95, 2529. (2) For example: (a) Grigor’ev, E. I.; Nesterov, S. V.; Trakhtenberg, L. I. Peculiarities of Sorption of Metal Ions on Immobilized Crown Ethers. Russ. J. Phys. Chem. (Translated from Zh. Fiz. Khim.) 1995, 69, 1573. (b) Macrocyclic Compounds in Analytical Chemistry. In Chemical Analysis. A Series of Monographs on Analytical Chemistry and Its Applications; Zolotov, Yu. A., Ed.; Wiley: New York, 1997; Vol. 143, Chapter 4. (3) Talanova, G. G.; Yatsimirskii, K. B.; Zitsmanis, A. Kh. Complexes of Polymer-Bound Crown Ethers with Alkali Metal Salts Having the Properties of an Anion Exchanger. Dokl. Chem. (Translated from Dokl. Akad. Nauk SSSR) 1991, 319, 210. (4) For example: (a) Olsher, U.; Hankins, M. G.; Kim, D. Y.; Bartsch, R. A. Anion Effect on Selectivity in Crown Ether Extraction of Alkali Metal Cations. J. Am. Chem. Soc. 1993, 115, 3370. Yakshin, V. V.; Abashkin, V. M.; Laskorin, B. M. Effect of Anions on the Extraction of Alkali Metal Salts by Crown Ethers. Dokl. Chem. (Translated from Dokl. Akad. Nauk SSSR) 1980, 319, 213. (b) Lamb, J. D.; Christensen, J. J.; Izatt, S. R.; Bedke, K.; Astin, M. S.; Izatt, R. M. Effects of Salt Concentration and Anion on the Rate of Carrier-Facilitated Transport of Metal Cations Through Bulk Liquid Membranes Containing Crown Ethers. J. Am. Chem. Soc. 1980, 102, 3399. Yatsimirskii, K. B.; Talanova, G. G. AnionTransport Properties of Macrocyclic Polyethers. Dokl. Chem. (Translated from Dokl. Akad. Nauk SSSR) 1983, 273, 414.
(5) Sorption of platinide ions by polymer-supported macrocycles with soft nitrogen donor atoms was reported earlier (for example, see ref 2b, pp 186-7 and 223). (6) Talanova, G. G.; Kozachkova, A. N.; Yatsimirskii, K. B.; Kravchenko, O. V.; Zitsmanis, A. Kh. Complexation of Potassium Tetrachloropalladate(II) with Polymer-Bonded Crown Ethers. Russ. J. Coord. Chem. (Translated from Koord. Khim.) 1996, 22, 258. (7) Yatsimirskii, K. B.; Talanova, G. G.; Kozachkova, A. N.; Kravchenko, O. V.; Zitsmanis, A. Kh. Complexation of Potassium Tetrachloroplatinite(II) with Polymer-Bonded Crown Ethers. Ukr. Khim. Zh. 1997, 63, 73 (Russ.); Chem. Abstr. 1999, 130, 162282y. (8) Zitsmanis, A. Kh.; Klyavinsh, M. K.; Roska, A.; Kalninya, I. R. Method of Preparation of Polymer-Bonded Crown Ethers, Inventor’s Certificate No. 1288186 (USSR); Byull. Izobret. 1987, 86 (Russ.). (9) Smith, R. M.; Martell, A. E. Critical Stability Constants; Plenum Press: New York, 1976; Vol. 4, p 107. (10) CRC Handbook of Chemistry and Physics, 65th ed.; Weast, R. C., Ed.; CRC Press: Boca Raton, FL, 1985; pp B-121 and B-124. (11) Standard Potentials in Aqueous Solution; Bard, A. I., Parson, R., Jordan, Y., Eds.; Marcel Dekker: New York, 1985; p 834. (12) (a) Cotton, A. F.; Wilkinson, G. F. R. S. Advanced Inorganic Chemistry, 3rd ed.; Wiley: New York, 1971. (b) Volchenskova, I. I.; Yatsimirskii, K. B. Charge-Transfer Bands and Conformation of Palladium Chloride Solvates in Certain Donor Solvents. Theor. Exp. Chem. (Translated from Teor. Eksp. Khim.) 1977, 13, 146. (13) Lever, A. B. P. Inorganic Electronic Spectroscopy, 2nd ed.; Elsevier: New York, 1984. (14) Bellamy, L. J. The Infrared Spectra of Complex Molecules, 3rd ed.; Wiley: New York, 1975; Vol. 1, p 84. (15) Talanova, G. G.; Elkarim, N. S. A.; Talanov, V. S.; Hanes, R. E., Jr.; Hwang, H.-S.; Bartsch, R. A.; Rogers, R. D. The “Picrate Effect” on Extraction Selectivities of Aromatic Group-Containing Crown Ethers for Alkali Metal Cations. J. Am. Chem. Soc. 1999, 121, 11281. (16) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; Wiley: New York, 1997.
Received for review January 18, 2000 Revised manuscript received July 28, 2000 Accepted July 28, 2000 IE0000616
