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γ-Zirconium and γ-titanium phosphate palladium intercalation compounds: synthesis and characterization by X-ray diffraction and thermal analyses
Materials Research Bulletin, Vol. 33, No. 11, pp. 1635–1652, 1998 Copyright © 1998 Elsevier Science Ltd Printed in the USA. All rights reserved 0025-5408/98 $19.00 1 .00
PII S0025-5408(98)00163-9
g-ZIRCONIUM AND g-TITANIUM PHOSPHATE PALLADIUM INTERCALATION COMPOUNDS: SYNTHESIS AND CHARACTERIZATION BY X-RAY DIFFRACTION AND THERMAL ANALYSES
C. Ferragina1*, P. Cafarelli1, and P. Giannoccaro2 CNR, IMAI, via Salaria Km. 29.300, 00016 Monterotondo (Roma), Italy 2 Dip. di Chimica, Universita` di Bari, via Amendola 173, 70126 Bari, Italy 1
(Refereed) (Received January 29, 1998; Accepted April 9, 1998)
ABSTRACT g-Zirconium and g-titanium phosphates (g-ZrP, g-TiP) with layered structure are well known as ion exchangers as well as agents intercalating organic bases. In the latter case, the intercalation compounds may exchange transition metal ions coordinated by the ligands, giving rise to in situ formed complexes. We prepared phases derived from g-ZrP, containing organic diamines (gZrPL) (L 5 ligand), such as 2,29-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmp). These materials exchange Pd21 ions when they are in batch contact with a PdCl2 solution and this produces solids with Pd21/L 5 1. The X-ray diffraction (XRD) patterns of some materials containing Pd21 showed an increase of 2 Å in d002. The differential thermal analysis (DTA) curves of the Pd21 materials showed a lowering of diamine temperature decomposition (100°C) with respect to those of their precursors. In the case of g-TiP, we also obtained intercalation compounds with the above-mentioned diamines. Similar experiments showed that g-TiPL exchanges very few Pd21 ions, except for the one derived from g-TiPdmp. The thermogravimetric (TG) curves show the same lowering of ligand temperature decomposition for all materials except g-TiPPdphen. The XRD patterns for all g-ZrPPdL and g-TiPPdL materials show peaks at dhkl 5 7.89, 8.59 – 8.04, and 9.31 Å, for compounds containing Pdbipy, Pdphen, and Pddmp, respectively. Due to the correspondent complexes into the exchanger, these peaks disappeared when the materials, except for those containing the Pddmp complex, were stirred into CH2Cl2. © 1998 Elsevier Science Ltd
*To whom the correspondence should be addressed. 1635
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KEYWORDS: A. layered compounds, A. organometallic compounds, B. intercalation reaction, C. X-ray diffraction
INTRODUCTION Considerable research effort has recently been devoted to the study of inorganic layered solids such as zirconium and titanium phosphate ion-exchangers. These layered crystalline insoluble acid salts exist in at least two modifications, usually indicated as a [1] and g [2] phases, which differ in the structure of the molecule macroanions [3,4]. Both these phases have been, in recent years, the object of growing interest for their peculiar ability either to exchange transition metal ions (tmi) [5–7] or to intercalate polar molecules [8 –13]. Some intercalation compounds can, in turn, exchange and coordinate tmi, to obtain the in-situ formed complexes. We have already studied a- and g-zirconium phosphates (a-ZrP, g-ZrP) and g-titanium phosphate (g-TiP) intercalated with organic molecules such as 2,29-bipyridyl, 1,10-phenanthroline and 2,9-dimethyl, 1,10-phenanthroline exchanged with ions of the first and the second row of tmi [14 –19]. The materials thus obtained can be utilized in heterogeneous catalysis, instead of the materials generally used in homogeneous catalysis [20 –23]. The possibility of intercalating active substrate makes these layered exchangers a suitable support for heterogeneous catalysis. Since these compounds may be used as catalysts, information on their thermal stability and the chemical and physical state is altogether of great interest, in order to correlate the catalytic activity with the course of a reaction under study. In recent years our interest has been focused on the rhodium materials derived from a-ZrP and g-ZrP intercalation compounds because rhodium materials are increasingly employed in various important homogeneous catalytic processes [20,24]. The a- and g-rhodium zirconium phosphates materials have been tested in some oxidative catalysts reactions, with good results [25,26]. For the same catalytic tests, such as the oxidative carbonylation of aniline, we have already studied the g-zirconium intercalation compounds as supports for palladium ions [27,28]. On the other hand, the support of the palladium(II) on layered exchangers have already been studied using zirconium phosphonates [29,30] and the resulting catalyst revealed the material to be active in several hydrogenation and hydroformylation processes. Previous studies showed that some ligand palladium complexes are potential anti-cancer agents as well as metal complexes [31–34]. In view of the importance of palladium complexes as potential anti-cancer drugs or as catalytic support for heterogeneous catalysis, we wanted to extend the study to the Pd21 ion exchanged in g-ZrP and g-TiP, previously intercalated with the above-mentioned organic diamines, to define the composition, structural definition, and thermal stability of these materials. We also wanted to determine the influence of different factors (matrix, ligand, tetravalent metal Zr or Ti, temperature and time of the experience) on the in situ formation of Pd– organic species and to verify the most suitable host phase and its use in heterogeneous catalysis, in respect to the a-analog ones.
EXPERIMENTAL PROCEDURE Chemicals. Palladium(II) chloride and organic diamines were Fluka purissimum products and were used as received.
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Intercalation Compounds. The starting materials g-Zr(PO4)(H2PO4)g2H2O and g-Ti(PO4)(H2PO4)z2H2O were prepared hydrothermally, according to the method of Yamanaka and Tanaka [35] and Allulli et al. [36]. g-ZrP intercalation compounds were obtained by first pre-swelling g-ZrP with ethanol (1 g of g-ZrP in batch contact with 100 mL of anhydrous EtOH for 24 h). The resulting g-ZrP–EtOH (d002516.6 Å) was then treated with 500 mL of a 0.1 mol dm23 or 0.01 mol dm23 H2O–EtOH (1:1) solution of bipy, or phen or dmp, for several days, at 45°C, as reported in the literature [37]. The solids were then filtered, washed with ethanol, and air dried at rt. Five intercalation materials were obtained with the formula compositions g-Zr(PO4)(H2PO4)bipy0.26z1.64H2O[g-ZrP(bipy)0.26]; g-Zr(PO4)(H2PO4)bipy0.44z0.30H2O[g-ZrP(bipy)0.44]; g-Zr(PO4)(H2PO4)dmp0.26z1.73H2O[g-ZrP(dmp)0.26]; g-Zr(PO4)(H2PO4)dmp0.44z 2.98H2O[g-ZrP(dmp)0.44]; and g-Zr(PO4)(H2PO4)phen0.44z2.04H2O[g-ZrP(phen)0.44]. g-TiP intercalation compounds were obtained by first pre-swelling g-TiP with ethanol (1 g of g-TiP in batch contact with 100 mL of anhydrous EtOH, for 24 h). The resulting g-TiPEtOH (d002 5 15.2 Å) was then treated with 500 mL of a 0.01 mol dm23 H2O–EtOH (1:1) solution of bipy, or phen or dmp, for 6 days, at 45°C. The solids were filtered, washed with ethanol. and air dried at room temperature. Three intercalation compounds with the formula compositions of g-Ti(PO4)(H2PO4)bipy0.43z0.53H2O[g-TiP(bipy)0.43], g-Ti(PO4)(H2PO4)phen0.47z1.48H2O[gTiP(phen)0.47], and g-Ti(PO4)(H2PO4)dmp0.26z2.83H2O[g-TiP(dmp)0.26] were obtained. Palladium Intercalation Compounds. A series of samples of g-ZrP or g-TiP intercalation compounds were mixed with a stock solution of Pd21 such that [Pd21]:[diamine intercalated] 5 1. The Pd21 uptake either by g-ZrP or g-TiP intercalation compounds was carried out by the batch procedure, at 25 or 45°C, for different sets of time. The suspensions were then filtered and the supernatant analyzed for the Pd21 content and the pH decrease (which is a consequence of the Pd21/H1 ion exchange process of the incoming metal ions with the dihydrogenphosphate group) was measured. Physical Measurements and Chemical Analysis. A simultaneous thermoanalyzer Stanton model STA 1500 was used for determining the amine and water contents of the materials. Samples were heated in platinum crucibles at a heating rate 10°C min21, ignition up to 1100°C to constant weight, in an air flow. Metal ion content was determined by following the concentration changes in the supernatants by atomic absorption spectrometry, using a GBC 903 instrument. Powder X-ray diffraction patterns of the materials were taken on a Philips automated diffractometer (model PW 1130/00) using Ni-filtered Cu Ka radiation (l 5 1.541 Å), with 2u angles believed accurate to 0.05°. RESULTS AND DISCUSSION Palladium Uptake by g-ZrP(bipy)0.44, g-ZrP(phen)0.44, and g-ZrP(dmp)0.44. 1 mmol samples of g-ZrP(bipy)0.44, g-ZrP(phen)0.44, or g-ZrP(dmp)0.44 were mixed for several sets of time, in batch, at 25 and 45°C, with portion of PdCl2 solution of 0.001 mol dm23 such that [Pd21]:[intercalated diamine] 5 1. The 1:1 molar ratio was chosen in order to favor the formation of complex species in the exchanger; the time periods were chosen from 0.5 to 144 h, in order to discover the parameters that influence the uptake kinetics (e.g., ligand, temperature). Table 1 shows the formula composition and the interlayer distance (d002) of the zirconium palladium intercalated materials, obtained at 45°C, according to contact time. The
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TABLE 1 Chemical Composition and Interlayer Distance of the g-ZrPPdL0.44 Materials d002 (Å)
Time (h)
Materials derived by g-ZrP(bipy)0.44z0.3H2O, d002 5 14.02 Å g-ZrPH1.92Pd0.04bipy0.44z0.27H2O g-ZrPH1.88Pd0.06bipy0.44z0.28H2O g-ZrPH1.80Pd0.10bipy0.44z0.62H2O g-ZrPH1.50Pd0.25bipy0.44z0.67H2O g-ZrPH1.48Pd0.26bipy0.44z1.18H2O g-ZrPH1.40Pd0.30bipy0.44z1.54H2O g-ZrPH1.40Pd0.30bipy0.44z1.54H2O
14.02 14.02 14.02 14.02 16.05 1 14.02 16.05 1 14.02 16.05 1 14.02
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-ZrP(phen).44z2.04H2O, d002 5 18.40 Å g-ZrPH1.86Pd0.07phen0.44z1.55H2O g-ZrPH1.70Pd0.15phen0.44z1.73H2O g-ZrPH1.60Pd0.20phen0.44z1.86H2O g-ZrPH1.46Pd027phen0.44z2.20H2O g-ZrPH1.36Pd0.32phen0.44z2.30H2O g-ZrPH1.28Pd0.36phen0.44z2.48H2O g-ZrPH1.28Pd0.36phen0.44z2.48H2O
18.40 16.67 16.67 20.53 1 16.67 20.53 1 16.67 20.53 1 16.67 20.53 1 16.67
0.5 1 3 6 24 72 144
Materials derived by g-ZrP(dmp)0.44z1.80H2O, d002 5 19.84 Å g-ZrPH1.44Pd0.28dmp0.44z2.00H2O g-ZrPH1.30Pd0.35dmp0.44z2.00H2O g-ZrPH1.22Pd0.39dmp0.44z2.20H2O g-ZrPH1.20Pd0.40dmp0.44z2.30H2O g-ZrPH1.20Pd0.40dmp0.44z2.30H2O g-ZrPH1.18Pd0.41dmp0.44z2.34H2O g-ZrPH1.18Pd0.41dmp0.44z2.54H2O
19.84 19.84 16.91 16.91 16.91 15.76 15.76
0.5 1.0 3.0 6.0 24.0 72.0 144.0
results obtained at 25°C showed that the palladium uptake was lower than in the case of the experiments performed at 45°C. We can confirm the importance of the temperature in the ion uptake and for this reason we want to show the characterization of the materials obtained at 45°C. The g-ZrPL0.44 materials behaved in a similar way when they exchanged palladium ions. The entity and speed of uptake was in the order of dmpphenbipy. After 24 h, the precursors, when contacted with PdCl2 solution, had already almost reached the maximum palladium content; after this time the uptake was very slow and did not increase markedly. g-ZrP(bipy)0.44 exchanged few Pd21 ions during the early stage of batch contact and these few palladium entities had a catalytic effect for the exchange that followed. It was only for g-ZrP(dmp)0.44 that we already had a molar ratio [Pd21]:[L] ; 1 after 3 h. At the same time, as can be seen from Table 1, we had a molar ratio Pd21:L 5 0.5 and Pd21:L 5 0.25, respectively for g-ZrP(phen)0.44 and g-ZrP(bipy)0.44. The water content increased with the Pd21 ions increase. This could be due to the coordination water of the tmi. The experiments performed at 25°C showed a very slow uptake, and the Pd21 content was almost half with respect to the experiments performed at 45°C for the same time periods. Not all materials had diamine elution during the ion exchange, as sometimes happens in the ion exchange with some tmi [38].
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TABLE 2 Chemical Composition and Interlayer Distance of the g-ZrPPdL0.26 Materials d002 (Å)
Time (h)
Materials derived by g-ZrP(bipy)0.26z1.80H2O, d002 5 14.47 Å g-ZrPH1.86Pd0.07bipy0.26z1.54H2O g-ZrPH1.78Pd0.11bipy0.26z1.90H2O g-ZrPH1.70Pd0.15bipy0.26z1.98H2O g-ZrPH1.64Pd0.18bipy0.26z1.98H2O g-ZrPH1.56Pd0.22bipy0.26z2.02H2O g-ZrPH1.56Pd0.22bipy0.26z2.05H2O g-ZrPH1.56Pd0.22bipy0.26z2.30H2O
14.47 14.47 14.97 14.97 14.73 14.73 14.73
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-ZrP(dmp)0.26z1.93H2O, d002 5 16.97 Å g-ZrPH1.88Pd0.06dmp0.26z1.94H2O g-ZrPH1.86Pd0.07dmp0.26z1.90H2O g-ZrPH1.76Pd0.12dmp0.26z1.96H2O g-ZrPH1.66Pd0.17dmp0.26z2.00H2O g-ZrPH1.48Pd0.26dmp0.26z2.105H2O g-ZrPH1.48Pd0.26dmp0.26z2.15H2O g-ZrPH1.48Pd0.26dmp0.26z2.44H2O
16.97 16.97 16.97 16.97 16.97 16.97 16.97
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Palladium Uptake by g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26. The same experiments, as described above, were performed with the materials derived from g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26. Table 2 shows the chemical composition of the zirconium palladium materials according to the contact time. We obtained materials with maximum uptake after 24 h. The kinetic uptake of the Pd21 ions was faster for g-ZrP(bipy)0.26 than for g-ZrP(dmp)0.26. If we compare the kinetic uptake with regard to palladium ion by the intercalation compounds with the same diamine, but different content (Lx, x 5 0.26 and 0.44), we note that in the case of bipy, g-ZrP(bipy)0.26 was faster than g-ZrP(bipy)0.44. In contrast, g-ZrP(dmp)0.26 was slower than g-ZrP(dmp)0.44. The obtained compounds did not show any diamine elution. From the XRD patterns of the palladium g-zirconium phosphate intercalation materials, we deduced that most compounds were quite amorphous because their peaks were broadened; in all cases a layered structure was maintained. The interlayer distance of the materials with the maximum palladium content (obtained after 6 days) derived from g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26 did not change in respect to that of their precursors. The behavior of g-ZrP(phen)0.44 during the palladium uptake was unique because, first of all, there was a decrease of 2 Å (16.67 vs. 18.40 Å). When the uptake was almost completed after 24 h, we noted two phases of similar intensity, one with a value of 20.53 Å and the other of 16.67 Å. For the material derived from g-ZrP(bipy)0.44, we noted a double phase, one increased by 2 Å with respect to its precursor and the other one the same as its precursor. As far as the palladium material derived by g-ZrP(dmp)0.44 is concerned, we saw a decrease of 4 Å after the complete uptake of the palladium ions. We observed all these interlayer variations, either as increases or as decreases, after 3 days of batch contact, when the ion exchange was almost completed and the PdL complex formed and stabilized between the layers of the exchangers. It appears that these intercalation materials with high ligand content after palladium uptake needed more time to arrange the PdL complex between the layers, due to the larger steric
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hindrance of the ligands. Generally, the XRD patterns for all the palladium materials already showed some peaks related to the PdL (L 5 bipy, phen, dmp) complexes in the experiments performed at 0.5 h of batch contact. The values of these peaks were 7.82 Å (sharpened and of high intensity) and 4.55 Å (sharpened and small) for the materials derived by g-ZrP(bipy)(0.26 – 0.44) exchangers. We also observed peaks with values of 8.49 Å (sharpened and small) and 8.18 Å (sharpened and of high intensity) for the materials derived by g-ZrP(phen)0.44 and a small peak with the value 9.3 Å for the materials derived by g-ZrP(dmp)(0.26 – 0.44). For all these palladium materials, the peaks were evident when the molar ratio Pd21/g-ZrPL was 0.10. We had confirmation that the previous peaks were related to the PdL complexes, because we synthesized the Pdbipy, Pdphen, and Pddmp complexes and their XRD patterns showed those peaks. In Figure 1 the XRD patterns of the g-ZrPPdL0.44 materials are shown. When the materials were heated at 500°C, the peaks related to Pd0 appeared at dhkl 5 2.24 and 1.94 Å [39]. Figures 2 and 3 show the TG-DTA curves of the g-ZrP palladium intercalation compounds (materials obtained at 45°C, after 6 days) compared with those of their precursors. Figure 2 shows the weight loss of the g-ZrPPdL samples in comparison with that of their parent compounds. For all the obtained materials, two big losses are observed in the TG curves: the first related to the elimination of interlamellar and coordination water occurred between 25 and 250°C; the second loss, in the range of 25– 850°C, was related either to the decomposition of the organic diamine or to the loss of water due to the condensation of the existing hydrogen phosphate group to the zirconium pyrophosphate phase. The decomposition of the organic ligand took place at different temperatures, depending on the diamine present, the last traces of carbonaceous residuals being completely lost at 1100°C. The TG curves are very similar to those of the analog precursors; the marked differences were for the materials derived by g-ZrP(phen)0.44, g-ZrP(dmp)0.44, and g-ZrP(dmp)0.26, for which we observed that the losses due to the ligand decomposition happened at lower (80°C) temperatures than those of their parents. For the materials derived by g-ZrP(bipy)0.26 and g-ZrP(bipy)0.44, this effect was less pronounced; this could be a consequence of the good catalytic effect of the palladium on the complete oxidation of the carbon formed in the solid, during the ligand decomposition. We had confirmation of that from the analog DTA curves, which show the exothermic peaks, related to the diamine decomposition, at lower temperatures than those of their parents, as we can see in Figure 3. We can also see from this figure that the diamine decomposition happened in two steps: a big exothermic peak appears between 400 and 500°C and a small peak between 300 and 400°C. We suppose that the latter peak is related to the PdL on the ion-exchanger surface because it disappeared when the materials dispersed were stirred into CH2Cl2. The DTA curves of the palladium materials show another difference in respect to the curves of their precursors: in the DTA curves of the palladium materials, the exothermic peak related to the transformation of layered pyrophosphate to the alpha cubic pyrophosphate happened at temperatures lower than that of their precursors (900 vs. 1000°C). Therefore we can affirm that some thermal behaviors are accelerated by the transition metal ion, in this case, by the palladium ion. Palladium Uptake by g-TiP(bipy)0.43, g-TiP(phen)0.47, and g-TiP(dmp)0.26. With the materials derived from g-TiP, we performed the same experiments as in the case of g-ZrP. Samples of 1 mmol of g-TiP(bipy)0.43, g-TiP(phen)0.47, or g-TiP(dmp)0.26 were mixed, for several sets of time, in batch, at 25 and 45°C, with a portion of PdCl2 solution of 0.001 mol
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FIG. 1 XRD patterns of (a) g-ZrPH1.48Pd0.26bipy0.44z1.18H2O, (b) g-ZrPH1.60Pd0.20phen0.44z1.86H2O, and (c) g-ZrPH1.22Pd0.39dmp0.44z2.20H2O materials. The arrows (2) show the related PdL complexes.
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FIG. 2 TG curves of g-ZrPPdL materials (solid line) vs. those of their precursors g-ZrPL (dotted line).
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FIG. 3 DTA curves of g-ZrPPdL materials (solid line) vs. those of their precursors g-ZrPL (dotted line).
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TABLE 3 Chemical Composition and Interlayer Distance of the g-TiPPdL Materials d002 (Å)
Time (h)
Materials derived by g-TiP(bipy)0.43z0.53H2O, d002 5 14.59 Å g-TiPH1.92Pd0.04bipy0.43z0.78H2O g-TiPH1.90Pd0.05bipy0.43z0.80H2O g-TiPH1.90Pd0.05bipy0.43z0.80H2O g-TiPH1.88Pd0.06bipy0.43z0.80H2O g-TiPH1.88Pd0.06bipy0.43z0.82H2O g-TiPH1.82Pd0.09bipy0.43z0.85H2O g-TiPH1.82Pd0.09bipy0.43z0.85H2O
14.59 14.59 14.59 14.59 14.59 14.59 14.59
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-TiP(phen)0.47z1.48H2O, d002 5 17.46 Å g-TiPH1.98Pd0.01phen0.47z1.50H2O g-TiPH1.94Pd0.03phen0.47z1.56H2O g-TiPH1.92Pd0.04phen0.47z1.60H2O g-TiPH1.90Pd0.05phen0.47z1.64H2O g-TiPH1.84Pd0.08phen0.47z1.65H2O g-TiPH1.76Pd0.12phen0.47z1.73H2O g-TiPH1.64Pd0.18phen0.47z1.74H2O
17.46 17.46 17.46 17.46 17.46 17.46 17.46
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-TiP(dmp)0.26z2.83H2O, d002 5 17.87 Å g-TiPH1.70Pd0.15dmp0.26z2.52H2O g-TiPH1.62Pd0.19dmp0.26z2.70H2O g-TiPH1.60Pd0.20dmp0.26z2.80H2O g-TiPH1.60Pd0.20dmp0.26z2.90H2O g-TiPH1.60Pd0.20dmp0.26z3.47H2O g-TiPH1.60Pd0.20dmp0.26z3.50H2O g-TiPH1.60Pd0.20dmp0.26z3.52H2O
17.87 17.87 17.87 17.87 17.87 17.87 17.87
0.5 1.0 3.0 6.0 24.0 72.0 144.0
dm23 such that [Pd21]:[intercalated diamine] 5 1. Also in this case we noted that the experiments performed at rt gave materials with a lower content of palladium ions. For the experiments performed at 45°C, we noted that the palladium uptake was in the order dmp . phen . bipy and the uptake behavior was different in respect to the analog g-ZrPL. In Table 3 we show the chemical composition of the obtained materials at different equilibration times. So we can see that, in respect to the palladium materials obtained from the analog g-ZrP(bipy)0.44 and g-ZrP(phen)0.44, the ion uptake was very low and very slow in the case of g-TiP(bipy)0.43 and g-TiP(phen)0.47. We did not reach in the solid a ratio [Pd21]: [intercalated diamine] 5 1 or 0.5. Only in the case of g-TiP(dmp)0.26 was the palladium uptake similar to that observed for g-ZrP(dmp)0.26 and faster, but the uptake did not exceed 0.2 mol Pd21/mole exchanger. As in the case of the g-zirconium palladium intercalation compounds, the materials obtained did not show any diamine elution. As we can observe in Table 3, the d002 of the g-TiPPdL did not change in respect to that of their precursors. In these cases, however, we also noted peaks related to the PdL (L 5 bipy, phen, dmp) complexes, even if the palladium content in these materials was lower than 0.10 mol/mole exchanger. So we can state that the presence of the PdL peaks is not related to the entity of the complexes as in the case of materials derived by g-ZrPL. The value of
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FIG. 4 TG-DTA curves of g-TiPPdL materials (solid line) vs. those of their precursors g-TiPL (dotted line).
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FIG. 5 TG curves of g-ZrPPdL materials (solid line) vs. those after their treatment with CH2Cl2 (dotted line).
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FIG. 6 DTA curves of g-ZrPPdL materials (solid line) before vs. after (dotted line) their treatment with CH2Cl2.
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FIG. 7 TG-DTA curves of g-TiPPdL materials before (solid line) vs. after (dotted line) their treatment with CH2Cl2.
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FIG. 8 XRD patterns of g-TiPbipy0.43Pd and g-TiPphen0.47Pd materials before (solid line) vs. after (dotted line) their treatment with CH2Cl2. these peaks were the same as those observed in the case of Pdbipy, Pdphen, and Pddmp for the palladium materials obtained from g-ZrPL. In the materials heated at 500°C, we obtained Pd0, as in the case of the materials derived from g-ZrPPdL. Figure 4 shows the TG-DTA curves of the g-TiP palladium intercalation compounds
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(materials obtained at 45°C, after 6 days) compared with those of their precursors. The TG curves of the materials containing palladium are quite similar to those of their parents, except for the material derived by g-TiP(bipy)0.43. This compound showed two different weight losses: a small loss in the range 250 –380°C and a big one in the range 380 –700°C. In contrast, its parent presented two equal losses in the same ranges. In the correspondent DTA curves there are two exothermic peaks, with different entities, at the same temperatures as in the TG curves: we can deduce that the thermal effect at 250 –380°C may be related to the presence of Pdbipy complex. As far as g-TiP(phen)0.47 and g-TiP(dmp)0.26 exchanged with palladium ions, the TG curves are similar to those of their parents, but there are some differences in the DTA curves. In fact, the palladium material derived by g-TiP(phen)0.47 had a new small peak at 380°C (as in the case of g-TiPPdbipy) and a large peak occurred at 520°C, compared with one at 480°C for the correspondent precursor. The g-TiPPddmp0.26 DTA curve shows three peaks in the range 330 – 480°C: the peak at 330°C was related to the decomposition of the Pddmp complex (as preview materials), the other two peaks were related to the ligand desorption and their decomposition temperature was lower than that of its precursor. All the PdL materials show the exothermic peak due to the transition phase of layered pyrophosphate into alpha cubic pyrophosphate at temperatures lower than that (70°C) of their precursors. Solubility. In either the XRD patterns or the DTA curves, all the palladium materials derived by g-ZrPL and by g-TiPL showed the presence of the PdL complexes in the exchanger. In the XRD patterns, we saw peaks at 7.82 and 4.55 Å for Pdbipy; at 8.49 Å for Pdphen, and at 9.3 Å for Pddmp. In the DTA curves, the presence of these complexes was related to the small exothermic peak between 300 and 400°C. The palladium materials derived from g-ZrPL and g-TiPL (except for those containing Pddmp) were stirred in a warm bath with CH2Cl2 for a couple of hours and then filtered, washed with EtOH, and air dried. Subsequently, the XRD peaks related to the PdL complex disappeared and the dhkl related to the Pd0 in the materials heated at 500°C decreased in intensity (40%). The DTA curves show the disappearance of the small exothermic peaks due to the PdL complex, as we saw earlier. In fact, for the palladium materials derived from the exchangers containing bipy or phen, the peak between 300 and 400°C disappeared after CH2Cl2 treatment. Figures 5, 6, and 7 show the TG-DTA curves of the g-ZrPPdL (L 5 bipy, phen) and g-TiPPdL materials before and after their treatment with the CH2Cl2 solution. The g-ZrPL and g-TiPL materials containing only the ligand, without the palladium ions, when stirred in a warm bath of CH2Cl2 did not show any diamine elution when analyzed using a simultaneous apparatus thermoanalyzer. However, in the case of g-ZrPPdL and g-TiPPdL materials, we obtained a diamine elution of g20% when these materials were stirred in a warm bath of CH2Cl2. Figure 8 shows the XRD patterns of g-TiPPdbipy and g-TiPPdphen before and after the treatment with CH2Cl2. Thus, we can affirm that the PdL complexes in the g-ZrP and g-TiP materials were almost solubilized when the materials were stirred in CH2Cl2. Since after the treatment we already had either Pd21 or ligands, even in less quantity, we can assume that either the complex remaining inside the exchanger was not eluted because the bond was stronger and so we solubilized the external complex weakly bonded, or not all the Pd21 ions exchanged into the intercalation compounds gave complexes with the intercalated diamines. In the latter case, the CH2Cl2 treatment did not solubilize palladium ions exchanged nor were diamines intercalated.
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ACKNOWLEDGMENTS We thank Mr. R. Di Rocco for his helpful technical assistance.
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PII S0025-5408(98)00163-9
g-ZIRCONIUM AND g-TITANIUM PHOSPHATE PALLADIUM INTERCALATION COMPOUNDS: SYNTHESIS AND CHARACTERIZATION BY X-RAY DIFFRACTION AND THERMAL ANALYSES
C. Ferragina1*, P. Cafarelli1, and P. Giannoccaro2 CNR, IMAI, via Salaria Km. 29.300, 00016 Monterotondo (Roma), Italy 2 Dip. di Chimica, Universita` di Bari, via Amendola 173, 70126 Bari, Italy 1
(Refereed) (Received January 29, 1998; Accepted April 9, 1998)
ABSTRACT g-Zirconium and g-titanium phosphates (g-ZrP, g-TiP) with layered structure are well known as ion exchangers as well as agents intercalating organic bases. In the latter case, the intercalation compounds may exchange transition metal ions coordinated by the ligands, giving rise to in situ formed complexes. We prepared phases derived from g-ZrP, containing organic diamines (gZrPL) (L 5 ligand), such as 2,29-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmp). These materials exchange Pd21 ions when they are in batch contact with a PdCl2 solution and this produces solids with Pd21/L 5 1. The X-ray diffraction (XRD) patterns of some materials containing Pd21 showed an increase of 2 Å in d002. The differential thermal analysis (DTA) curves of the Pd21 materials showed a lowering of diamine temperature decomposition (100°C) with respect to those of their precursors. In the case of g-TiP, we also obtained intercalation compounds with the above-mentioned diamines. Similar experiments showed that g-TiPL exchanges very few Pd21 ions, except for the one derived from g-TiPdmp. The thermogravimetric (TG) curves show the same lowering of ligand temperature decomposition for all materials except g-TiPPdphen. The XRD patterns for all g-ZrPPdL and g-TiPPdL materials show peaks at dhkl 5 7.89, 8.59 – 8.04, and 9.31 Å, for compounds containing Pdbipy, Pdphen, and Pddmp, respectively. Due to the correspondent complexes into the exchanger, these peaks disappeared when the materials, except for those containing the Pddmp complex, were stirred into CH2Cl2. © 1998 Elsevier Science Ltd
*To whom the correspondence should be addressed. 1635
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KEYWORDS: A. layered compounds, A. organometallic compounds, B. intercalation reaction, C. X-ray diffraction
INTRODUCTION Considerable research effort has recently been devoted to the study of inorganic layered solids such as zirconium and titanium phosphate ion-exchangers. These layered crystalline insoluble acid salts exist in at least two modifications, usually indicated as a [1] and g [2] phases, which differ in the structure of the molecule macroanions [3,4]. Both these phases have been, in recent years, the object of growing interest for their peculiar ability either to exchange transition metal ions (tmi) [5–7] or to intercalate polar molecules [8 –13]. Some intercalation compounds can, in turn, exchange and coordinate tmi, to obtain the in-situ formed complexes. We have already studied a- and g-zirconium phosphates (a-ZrP, g-ZrP) and g-titanium phosphate (g-TiP) intercalated with organic molecules such as 2,29-bipyridyl, 1,10-phenanthroline and 2,9-dimethyl, 1,10-phenanthroline exchanged with ions of the first and the second row of tmi [14 –19]. The materials thus obtained can be utilized in heterogeneous catalysis, instead of the materials generally used in homogeneous catalysis [20 –23]. The possibility of intercalating active substrate makes these layered exchangers a suitable support for heterogeneous catalysis. Since these compounds may be used as catalysts, information on their thermal stability and the chemical and physical state is altogether of great interest, in order to correlate the catalytic activity with the course of a reaction under study. In recent years our interest has been focused on the rhodium materials derived from a-ZrP and g-ZrP intercalation compounds because rhodium materials are increasingly employed in various important homogeneous catalytic processes [20,24]. The a- and g-rhodium zirconium phosphates materials have been tested in some oxidative catalysts reactions, with good results [25,26]. For the same catalytic tests, such as the oxidative carbonylation of aniline, we have already studied the g-zirconium intercalation compounds as supports for palladium ions [27,28]. On the other hand, the support of the palladium(II) on layered exchangers have already been studied using zirconium phosphonates [29,30] and the resulting catalyst revealed the material to be active in several hydrogenation and hydroformylation processes. Previous studies showed that some ligand palladium complexes are potential anti-cancer agents as well as metal complexes [31–34]. In view of the importance of palladium complexes as potential anti-cancer drugs or as catalytic support for heterogeneous catalysis, we wanted to extend the study to the Pd21 ion exchanged in g-ZrP and g-TiP, previously intercalated with the above-mentioned organic diamines, to define the composition, structural definition, and thermal stability of these materials. We also wanted to determine the influence of different factors (matrix, ligand, tetravalent metal Zr or Ti, temperature and time of the experience) on the in situ formation of Pd– organic species and to verify the most suitable host phase and its use in heterogeneous catalysis, in respect to the a-analog ones.
EXPERIMENTAL PROCEDURE Chemicals. Palladium(II) chloride and organic diamines were Fluka purissimum products and were used as received.
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Intercalation Compounds. The starting materials g-Zr(PO4)(H2PO4)g2H2O and g-Ti(PO4)(H2PO4)z2H2O were prepared hydrothermally, according to the method of Yamanaka and Tanaka [35] and Allulli et al. [36]. g-ZrP intercalation compounds were obtained by first pre-swelling g-ZrP with ethanol (1 g of g-ZrP in batch contact with 100 mL of anhydrous EtOH for 24 h). The resulting g-ZrP–EtOH (d002516.6 Å) was then treated with 500 mL of a 0.1 mol dm23 or 0.01 mol dm23 H2O–EtOH (1:1) solution of bipy, or phen or dmp, for several days, at 45°C, as reported in the literature [37]. The solids were then filtered, washed with ethanol, and air dried at rt. Five intercalation materials were obtained with the formula compositions g-Zr(PO4)(H2PO4)bipy0.26z1.64H2O[g-ZrP(bipy)0.26]; g-Zr(PO4)(H2PO4)bipy0.44z0.30H2O[g-ZrP(bipy)0.44]; g-Zr(PO4)(H2PO4)dmp0.26z1.73H2O[g-ZrP(dmp)0.26]; g-Zr(PO4)(H2PO4)dmp0.44z 2.98H2O[g-ZrP(dmp)0.44]; and g-Zr(PO4)(H2PO4)phen0.44z2.04H2O[g-ZrP(phen)0.44]. g-TiP intercalation compounds were obtained by first pre-swelling g-TiP with ethanol (1 g of g-TiP in batch contact with 100 mL of anhydrous EtOH, for 24 h). The resulting g-TiPEtOH (d002 5 15.2 Å) was then treated with 500 mL of a 0.01 mol dm23 H2O–EtOH (1:1) solution of bipy, or phen or dmp, for 6 days, at 45°C. The solids were filtered, washed with ethanol. and air dried at room temperature. Three intercalation compounds with the formula compositions of g-Ti(PO4)(H2PO4)bipy0.43z0.53H2O[g-TiP(bipy)0.43], g-Ti(PO4)(H2PO4)phen0.47z1.48H2O[gTiP(phen)0.47], and g-Ti(PO4)(H2PO4)dmp0.26z2.83H2O[g-TiP(dmp)0.26] were obtained. Palladium Intercalation Compounds. A series of samples of g-ZrP or g-TiP intercalation compounds were mixed with a stock solution of Pd21 such that [Pd21]:[diamine intercalated] 5 1. The Pd21 uptake either by g-ZrP or g-TiP intercalation compounds was carried out by the batch procedure, at 25 or 45°C, for different sets of time. The suspensions were then filtered and the supernatant analyzed for the Pd21 content and the pH decrease (which is a consequence of the Pd21/H1 ion exchange process of the incoming metal ions with the dihydrogenphosphate group) was measured. Physical Measurements and Chemical Analysis. A simultaneous thermoanalyzer Stanton model STA 1500 was used for determining the amine and water contents of the materials. Samples were heated in platinum crucibles at a heating rate 10°C min21, ignition up to 1100°C to constant weight, in an air flow. Metal ion content was determined by following the concentration changes in the supernatants by atomic absorption spectrometry, using a GBC 903 instrument. Powder X-ray diffraction patterns of the materials were taken on a Philips automated diffractometer (model PW 1130/00) using Ni-filtered Cu Ka radiation (l 5 1.541 Å), with 2u angles believed accurate to 0.05°. RESULTS AND DISCUSSION Palladium Uptake by g-ZrP(bipy)0.44, g-ZrP(phen)0.44, and g-ZrP(dmp)0.44. 1 mmol samples of g-ZrP(bipy)0.44, g-ZrP(phen)0.44, or g-ZrP(dmp)0.44 were mixed for several sets of time, in batch, at 25 and 45°C, with portion of PdCl2 solution of 0.001 mol dm23 such that [Pd21]:[intercalated diamine] 5 1. The 1:1 molar ratio was chosen in order to favor the formation of complex species in the exchanger; the time periods were chosen from 0.5 to 144 h, in order to discover the parameters that influence the uptake kinetics (e.g., ligand, temperature). Table 1 shows the formula composition and the interlayer distance (d002) of the zirconium palladium intercalated materials, obtained at 45°C, according to contact time. The
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TABLE 1 Chemical Composition and Interlayer Distance of the g-ZrPPdL0.44 Materials d002 (Å)
Time (h)
Materials derived by g-ZrP(bipy)0.44z0.3H2O, d002 5 14.02 Å g-ZrPH1.92Pd0.04bipy0.44z0.27H2O g-ZrPH1.88Pd0.06bipy0.44z0.28H2O g-ZrPH1.80Pd0.10bipy0.44z0.62H2O g-ZrPH1.50Pd0.25bipy0.44z0.67H2O g-ZrPH1.48Pd0.26bipy0.44z1.18H2O g-ZrPH1.40Pd0.30bipy0.44z1.54H2O g-ZrPH1.40Pd0.30bipy0.44z1.54H2O
14.02 14.02 14.02 14.02 16.05 1 14.02 16.05 1 14.02 16.05 1 14.02
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-ZrP(phen).44z2.04H2O, d002 5 18.40 Å g-ZrPH1.86Pd0.07phen0.44z1.55H2O g-ZrPH1.70Pd0.15phen0.44z1.73H2O g-ZrPH1.60Pd0.20phen0.44z1.86H2O g-ZrPH1.46Pd027phen0.44z2.20H2O g-ZrPH1.36Pd0.32phen0.44z2.30H2O g-ZrPH1.28Pd0.36phen0.44z2.48H2O g-ZrPH1.28Pd0.36phen0.44z2.48H2O
18.40 16.67 16.67 20.53 1 16.67 20.53 1 16.67 20.53 1 16.67 20.53 1 16.67
0.5 1 3 6 24 72 144
Materials derived by g-ZrP(dmp)0.44z1.80H2O, d002 5 19.84 Å g-ZrPH1.44Pd0.28dmp0.44z2.00H2O g-ZrPH1.30Pd0.35dmp0.44z2.00H2O g-ZrPH1.22Pd0.39dmp0.44z2.20H2O g-ZrPH1.20Pd0.40dmp0.44z2.30H2O g-ZrPH1.20Pd0.40dmp0.44z2.30H2O g-ZrPH1.18Pd0.41dmp0.44z2.34H2O g-ZrPH1.18Pd0.41dmp0.44z2.54H2O
19.84 19.84 16.91 16.91 16.91 15.76 15.76
0.5 1.0 3.0 6.0 24.0 72.0 144.0
results obtained at 25°C showed that the palladium uptake was lower than in the case of the experiments performed at 45°C. We can confirm the importance of the temperature in the ion uptake and for this reason we want to show the characterization of the materials obtained at 45°C. The g-ZrPL0.44 materials behaved in a similar way when they exchanged palladium ions. The entity and speed of uptake was in the order of dmpphenbipy. After 24 h, the precursors, when contacted with PdCl2 solution, had already almost reached the maximum palladium content; after this time the uptake was very slow and did not increase markedly. g-ZrP(bipy)0.44 exchanged few Pd21 ions during the early stage of batch contact and these few palladium entities had a catalytic effect for the exchange that followed. It was only for g-ZrP(dmp)0.44 that we already had a molar ratio [Pd21]:[L] ; 1 after 3 h. At the same time, as can be seen from Table 1, we had a molar ratio Pd21:L 5 0.5 and Pd21:L 5 0.25, respectively for g-ZrP(phen)0.44 and g-ZrP(bipy)0.44. The water content increased with the Pd21 ions increase. This could be due to the coordination water of the tmi. The experiments performed at 25°C showed a very slow uptake, and the Pd21 content was almost half with respect to the experiments performed at 45°C for the same time periods. Not all materials had diamine elution during the ion exchange, as sometimes happens in the ion exchange with some tmi [38].
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TABLE 2 Chemical Composition and Interlayer Distance of the g-ZrPPdL0.26 Materials d002 (Å)
Time (h)
Materials derived by g-ZrP(bipy)0.26z1.80H2O, d002 5 14.47 Å g-ZrPH1.86Pd0.07bipy0.26z1.54H2O g-ZrPH1.78Pd0.11bipy0.26z1.90H2O g-ZrPH1.70Pd0.15bipy0.26z1.98H2O g-ZrPH1.64Pd0.18bipy0.26z1.98H2O g-ZrPH1.56Pd0.22bipy0.26z2.02H2O g-ZrPH1.56Pd0.22bipy0.26z2.05H2O g-ZrPH1.56Pd0.22bipy0.26z2.30H2O
14.47 14.47 14.97 14.97 14.73 14.73 14.73
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-ZrP(dmp)0.26z1.93H2O, d002 5 16.97 Å g-ZrPH1.88Pd0.06dmp0.26z1.94H2O g-ZrPH1.86Pd0.07dmp0.26z1.90H2O g-ZrPH1.76Pd0.12dmp0.26z1.96H2O g-ZrPH1.66Pd0.17dmp0.26z2.00H2O g-ZrPH1.48Pd0.26dmp0.26z2.105H2O g-ZrPH1.48Pd0.26dmp0.26z2.15H2O g-ZrPH1.48Pd0.26dmp0.26z2.44H2O
16.97 16.97 16.97 16.97 16.97 16.97 16.97
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Palladium Uptake by g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26. The same experiments, as described above, were performed with the materials derived from g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26. Table 2 shows the chemical composition of the zirconium palladium materials according to the contact time. We obtained materials with maximum uptake after 24 h. The kinetic uptake of the Pd21 ions was faster for g-ZrP(bipy)0.26 than for g-ZrP(dmp)0.26. If we compare the kinetic uptake with regard to palladium ion by the intercalation compounds with the same diamine, but different content (Lx, x 5 0.26 and 0.44), we note that in the case of bipy, g-ZrP(bipy)0.26 was faster than g-ZrP(bipy)0.44. In contrast, g-ZrP(dmp)0.26 was slower than g-ZrP(dmp)0.44. The obtained compounds did not show any diamine elution. From the XRD patterns of the palladium g-zirconium phosphate intercalation materials, we deduced that most compounds were quite amorphous because their peaks were broadened; in all cases a layered structure was maintained. The interlayer distance of the materials with the maximum palladium content (obtained after 6 days) derived from g-ZrP(bipy)0.26 and g-ZrP(dmp)0.26 did not change in respect to that of their precursors. The behavior of g-ZrP(phen)0.44 during the palladium uptake was unique because, first of all, there was a decrease of 2 Å (16.67 vs. 18.40 Å). When the uptake was almost completed after 24 h, we noted two phases of similar intensity, one with a value of 20.53 Å and the other of 16.67 Å. For the material derived from g-ZrP(bipy)0.44, we noted a double phase, one increased by 2 Å with respect to its precursor and the other one the same as its precursor. As far as the palladium material derived by g-ZrP(dmp)0.44 is concerned, we saw a decrease of 4 Å after the complete uptake of the palladium ions. We observed all these interlayer variations, either as increases or as decreases, after 3 days of batch contact, when the ion exchange was almost completed and the PdL complex formed and stabilized between the layers of the exchangers. It appears that these intercalation materials with high ligand content after palladium uptake needed more time to arrange the PdL complex between the layers, due to the larger steric
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hindrance of the ligands. Generally, the XRD patterns for all the palladium materials already showed some peaks related to the PdL (L 5 bipy, phen, dmp) complexes in the experiments performed at 0.5 h of batch contact. The values of these peaks were 7.82 Å (sharpened and of high intensity) and 4.55 Å (sharpened and small) for the materials derived by g-ZrP(bipy)(0.26 – 0.44) exchangers. We also observed peaks with values of 8.49 Å (sharpened and small) and 8.18 Å (sharpened and of high intensity) for the materials derived by g-ZrP(phen)0.44 and a small peak with the value 9.3 Å for the materials derived by g-ZrP(dmp)(0.26 – 0.44). For all these palladium materials, the peaks were evident when the molar ratio Pd21/g-ZrPL was 0.10. We had confirmation that the previous peaks were related to the PdL complexes, because we synthesized the Pdbipy, Pdphen, and Pddmp complexes and their XRD patterns showed those peaks. In Figure 1 the XRD patterns of the g-ZrPPdL0.44 materials are shown. When the materials were heated at 500°C, the peaks related to Pd0 appeared at dhkl 5 2.24 and 1.94 Å [39]. Figures 2 and 3 show the TG-DTA curves of the g-ZrP palladium intercalation compounds (materials obtained at 45°C, after 6 days) compared with those of their precursors. Figure 2 shows the weight loss of the g-ZrPPdL samples in comparison with that of their parent compounds. For all the obtained materials, two big losses are observed in the TG curves: the first related to the elimination of interlamellar and coordination water occurred between 25 and 250°C; the second loss, in the range of 25– 850°C, was related either to the decomposition of the organic diamine or to the loss of water due to the condensation of the existing hydrogen phosphate group to the zirconium pyrophosphate phase. The decomposition of the organic ligand took place at different temperatures, depending on the diamine present, the last traces of carbonaceous residuals being completely lost at 1100°C. The TG curves are very similar to those of the analog precursors; the marked differences were for the materials derived by g-ZrP(phen)0.44, g-ZrP(dmp)0.44, and g-ZrP(dmp)0.26, for which we observed that the losses due to the ligand decomposition happened at lower (80°C) temperatures than those of their parents. For the materials derived by g-ZrP(bipy)0.26 and g-ZrP(bipy)0.44, this effect was less pronounced; this could be a consequence of the good catalytic effect of the palladium on the complete oxidation of the carbon formed in the solid, during the ligand decomposition. We had confirmation of that from the analog DTA curves, which show the exothermic peaks, related to the diamine decomposition, at lower temperatures than those of their parents, as we can see in Figure 3. We can also see from this figure that the diamine decomposition happened in two steps: a big exothermic peak appears between 400 and 500°C and a small peak between 300 and 400°C. We suppose that the latter peak is related to the PdL on the ion-exchanger surface because it disappeared when the materials dispersed were stirred into CH2Cl2. The DTA curves of the palladium materials show another difference in respect to the curves of their precursors: in the DTA curves of the palladium materials, the exothermic peak related to the transformation of layered pyrophosphate to the alpha cubic pyrophosphate happened at temperatures lower than that of their precursors (900 vs. 1000°C). Therefore we can affirm that some thermal behaviors are accelerated by the transition metal ion, in this case, by the palladium ion. Palladium Uptake by g-TiP(bipy)0.43, g-TiP(phen)0.47, and g-TiP(dmp)0.26. With the materials derived from g-TiP, we performed the same experiments as in the case of g-ZrP. Samples of 1 mmol of g-TiP(bipy)0.43, g-TiP(phen)0.47, or g-TiP(dmp)0.26 were mixed, for several sets of time, in batch, at 25 and 45°C, with a portion of PdCl2 solution of 0.001 mol
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FIG. 1 XRD patterns of (a) g-ZrPH1.48Pd0.26bipy0.44z1.18H2O, (b) g-ZrPH1.60Pd0.20phen0.44z1.86H2O, and (c) g-ZrPH1.22Pd0.39dmp0.44z2.20H2O materials. The arrows (2) show the related PdL complexes.
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FIG. 2 TG curves of g-ZrPPdL materials (solid line) vs. those of their precursors g-ZrPL (dotted line).
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FIG. 3 DTA curves of g-ZrPPdL materials (solid line) vs. those of their precursors g-ZrPL (dotted line).
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TABLE 3 Chemical Composition and Interlayer Distance of the g-TiPPdL Materials d002 (Å)
Time (h)
Materials derived by g-TiP(bipy)0.43z0.53H2O, d002 5 14.59 Å g-TiPH1.92Pd0.04bipy0.43z0.78H2O g-TiPH1.90Pd0.05bipy0.43z0.80H2O g-TiPH1.90Pd0.05bipy0.43z0.80H2O g-TiPH1.88Pd0.06bipy0.43z0.80H2O g-TiPH1.88Pd0.06bipy0.43z0.82H2O g-TiPH1.82Pd0.09bipy0.43z0.85H2O g-TiPH1.82Pd0.09bipy0.43z0.85H2O
14.59 14.59 14.59 14.59 14.59 14.59 14.59
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-TiP(phen)0.47z1.48H2O, d002 5 17.46 Å g-TiPH1.98Pd0.01phen0.47z1.50H2O g-TiPH1.94Pd0.03phen0.47z1.56H2O g-TiPH1.92Pd0.04phen0.47z1.60H2O g-TiPH1.90Pd0.05phen0.47z1.64H2O g-TiPH1.84Pd0.08phen0.47z1.65H2O g-TiPH1.76Pd0.12phen0.47z1.73H2O g-TiPH1.64Pd0.18phen0.47z1.74H2O
17.46 17.46 17.46 17.46 17.46 17.46 17.46
0.5 1.0 3.0 6.0 24.0 72.0 144.0
Materials derived by g-TiP(dmp)0.26z2.83H2O, d002 5 17.87 Å g-TiPH1.70Pd0.15dmp0.26z2.52H2O g-TiPH1.62Pd0.19dmp0.26z2.70H2O g-TiPH1.60Pd0.20dmp0.26z2.80H2O g-TiPH1.60Pd0.20dmp0.26z2.90H2O g-TiPH1.60Pd0.20dmp0.26z3.47H2O g-TiPH1.60Pd0.20dmp0.26z3.50H2O g-TiPH1.60Pd0.20dmp0.26z3.52H2O
17.87 17.87 17.87 17.87 17.87 17.87 17.87
0.5 1.0 3.0 6.0 24.0 72.0 144.0
dm23 such that [Pd21]:[intercalated diamine] 5 1. Also in this case we noted that the experiments performed at rt gave materials with a lower content of palladium ions. For the experiments performed at 45°C, we noted that the palladium uptake was in the order dmp . phen . bipy and the uptake behavior was different in respect to the analog g-ZrPL. In Table 3 we show the chemical composition of the obtained materials at different equilibration times. So we can see that, in respect to the palladium materials obtained from the analog g-ZrP(bipy)0.44 and g-ZrP(phen)0.44, the ion uptake was very low and very slow in the case of g-TiP(bipy)0.43 and g-TiP(phen)0.47. We did not reach in the solid a ratio [Pd21]: [intercalated diamine] 5 1 or 0.5. Only in the case of g-TiP(dmp)0.26 was the palladium uptake similar to that observed for g-ZrP(dmp)0.26 and faster, but the uptake did not exceed 0.2 mol Pd21/mole exchanger. As in the case of the g-zirconium palladium intercalation compounds, the materials obtained did not show any diamine elution. As we can observe in Table 3, the d002 of the g-TiPPdL did not change in respect to that of their precursors. In these cases, however, we also noted peaks related to the PdL (L 5 bipy, phen, dmp) complexes, even if the palladium content in these materials was lower than 0.10 mol/mole exchanger. So we can state that the presence of the PdL peaks is not related to the entity of the complexes as in the case of materials derived by g-ZrPL. The value of
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FIG. 4 TG-DTA curves of g-TiPPdL materials (solid line) vs. those of their precursors g-TiPL (dotted line).
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FIG. 5 TG curves of g-ZrPPdL materials (solid line) vs. those after their treatment with CH2Cl2 (dotted line).
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FIG. 6 DTA curves of g-ZrPPdL materials (solid line) before vs. after (dotted line) their treatment with CH2Cl2.
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FIG. 7 TG-DTA curves of g-TiPPdL materials before (solid line) vs. after (dotted line) their treatment with CH2Cl2.
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FIG. 8 XRD patterns of g-TiPbipy0.43Pd and g-TiPphen0.47Pd materials before (solid line) vs. after (dotted line) their treatment with CH2Cl2. these peaks were the same as those observed in the case of Pdbipy, Pdphen, and Pddmp for the palladium materials obtained from g-ZrPL. In the materials heated at 500°C, we obtained Pd0, as in the case of the materials derived from g-ZrPPdL. Figure 4 shows the TG-DTA curves of the g-TiP palladium intercalation compounds
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(materials obtained at 45°C, after 6 days) compared with those of their precursors. The TG curves of the materials containing palladium are quite similar to those of their parents, except for the material derived by g-TiP(bipy)0.43. This compound showed two different weight losses: a small loss in the range 250 –380°C and a big one in the range 380 –700°C. In contrast, its parent presented two equal losses in the same ranges. In the correspondent DTA curves there are two exothermic peaks, with different entities, at the same temperatures as in the TG curves: we can deduce that the thermal effect at 250 –380°C may be related to the presence of Pdbipy complex. As far as g-TiP(phen)0.47 and g-TiP(dmp)0.26 exchanged with palladium ions, the TG curves are similar to those of their parents, but there are some differences in the DTA curves. In fact, the palladium material derived by g-TiP(phen)0.47 had a new small peak at 380°C (as in the case of g-TiPPdbipy) and a large peak occurred at 520°C, compared with one at 480°C for the correspondent precursor. The g-TiPPddmp0.26 DTA curve shows three peaks in the range 330 – 480°C: the peak at 330°C was related to the decomposition of the Pddmp complex (as preview materials), the other two peaks were related to the ligand desorption and their decomposition temperature was lower than that of its precursor. All the PdL materials show the exothermic peak due to the transition phase of layered pyrophosphate into alpha cubic pyrophosphate at temperatures lower than that (70°C) of their precursors. Solubility. In either the XRD patterns or the DTA curves, all the palladium materials derived by g-ZrPL and by g-TiPL showed the presence of the PdL complexes in the exchanger. In the XRD patterns, we saw peaks at 7.82 and 4.55 Å for Pdbipy; at 8.49 Å for Pdphen, and at 9.3 Å for Pddmp. In the DTA curves, the presence of these complexes was related to the small exothermic peak between 300 and 400°C. The palladium materials derived from g-ZrPL and g-TiPL (except for those containing Pddmp) were stirred in a warm bath with CH2Cl2 for a couple of hours and then filtered, washed with EtOH, and air dried. Subsequently, the XRD peaks related to the PdL complex disappeared and the dhkl related to the Pd0 in the materials heated at 500°C decreased in intensity (40%). The DTA curves show the disappearance of the small exothermic peaks due to the PdL complex, as we saw earlier. In fact, for the palladium materials derived from the exchangers containing bipy or phen, the peak between 300 and 400°C disappeared after CH2Cl2 treatment. Figures 5, 6, and 7 show the TG-DTA curves of the g-ZrPPdL (L 5 bipy, phen) and g-TiPPdL materials before and after their treatment with the CH2Cl2 solution. The g-ZrPL and g-TiPL materials containing only the ligand, without the palladium ions, when stirred in a warm bath of CH2Cl2 did not show any diamine elution when analyzed using a simultaneous apparatus thermoanalyzer. However, in the case of g-ZrPPdL and g-TiPPdL materials, we obtained a diamine elution of g20% when these materials were stirred in a warm bath of CH2Cl2. Figure 8 shows the XRD patterns of g-TiPPdbipy and g-TiPPdphen before and after the treatment with CH2Cl2. Thus, we can affirm that the PdL complexes in the g-ZrP and g-TiP materials were almost solubilized when the materials were stirred in CH2Cl2. Since after the treatment we already had either Pd21 or ligands, even in less quantity, we can assume that either the complex remaining inside the exchanger was not eluted because the bond was stronger and so we solubilized the external complex weakly bonded, or not all the Pd21 ions exchanged into the intercalation compounds gave complexes with the intercalated diamines. In the latter case, the CH2Cl2 treatment did not solubilize palladium ions exchanged nor were diamines intercalated.
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ACKNOWLEDGMENTS We thank Mr. R. Di Rocco for his helpful technical assistance.
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