J. MATER. CHEM., 1991, 1(6), 1081-1082 1081 Crosslinked Layered Materials formed by Intercalation of Octameric Siloxanes in Metal(iv) Hydrogen Phosphates Jacques Roziere,* Deborah J. Jones and Thierry Cassagneau Laboratoire des Agregats Moleculaires et Materiaux Inorganiques, URA CNRS 79, Universite Montpellier 2, 34095 Montpellier Cedex 5,France The intercalation of octa(aminopropylsi1asesquioxane) into metal( tv) hydrogen phosphates [MI" =Zr, Ti, Sn] leads to silica crosslinked materials. The layered structure and the silica framework are retained after thermal processing. Bilayer formation is obtained with tin phosphate. Keywords: Siloxane; Phosphate ; Pillaring ; Crosslinking It is now well established that layered solids other than smectite clays may be pillared to form three-dimensional crosslinked materials, the porosity of which is ultimately tunable by the nature of the host substrate and of the chemical species acting as pillar.' The possibility of forming porous derivatives using inorganic pillaring agents and layered metal(1v) hydrogen phosphates of the a form was initially questioned on the basis of charge-density considerations and alternative routes, including pillaring with organic molecules or organic derivatization of the phosphate, were preferred.' Early results obtained on the crosslinking of a-zirconium phosphate by polyhydroxometallic ions would seem to vindi- cate this reasoning by giving only materials of low surface area;3 however, more recently, the synthesis of highly porous pillared tin phosphate has been rep~rted,~.~ although the origin of the porosity has been discussed.' An alternative synthetic pathway, designed to overcome the charge-density limitations associated with the insertion of inorganic pillars, lies in the use of organometallic guest molecules with expendable and bulky organic groups, remov- able by subsequent thermal processing.Oligosilasesquioxane routes to pillared a-zirconium phosphate were first suggested by Lewis et d6Here we report the formation of silica crosslinked zirconium, titanium and tin phosphates (ZrP, TiP and SnP, respectively) from aminopropyltriethoxysilane (APTEOS), hydrolytically polymerised ex situ to the octameric form [ZSiO, .5]8, where Z=(CH2)3NH3+.Preparation of octa(3-aminopropylsilasesquioxane) was undertaken following the synthetic criteria described by Voronkov and La~rent'yev.~ Thus APTEOS was diluted in ethanol-water (v/v = 14:1) to give a solution of concentration 0.45 mol dmP3, with stirring. "Si NMR spectroscopy of the solutions confirmed the nature of the constituent oligomer.? The outcome of intercalation reactions was found to depend on the nature of the alcohol, and methanol, isopropyl alcohol and isopentyl alcohol were also used. Expanded metal(1v) hydrogen phosphates were prepared by contacting 1 g of the solid, prepared according to published methodsg and sus-pended in deionised water (20 cm3), with aliquots of the above siloxane solution such that the molar ratio R =[Si ]/[M'"] lay in the range 0.2-3.0.After contact for 15 h to 5 days, the materials were separated by high-speed centrifugation, washed, and air-dried. Selected expanded phases were calcined in air, or under vacuum, at temperatures between 350 and 550 "C. The uptake of [H2N(CH2)3Si01.5]8 by ZrP, (Fig. 1; gravi-t Recorded at 49.6 kHz on a Bruker AC 250 spectrometer. A signal at -68 ppm, corresponding to the cyclic octamer [H2N(CH2)3SiOlJ8 is observed. A weak line discernible at -60 ppm probably arises from the presence of small amounts of trimeric species. /~~""~~~~~"~~" 0 2.5 5 7.5 10 12.5 Si added/mrnol g-'(ZrP) Fig. 1 Uptake of [H2N(CH2)3Si0,.,]8, by ZrP from aqueous etha- nolic solution metric determination of Si in the supernatant liquid as quino- line silicomolybdate) as a function of R shows that maximal insertion occurs above R =2.0, when 5.2 mmol Si per gram of ZrP are taken up, corresponding to an [Si] :[PI molar ratio of 0.79.Preliminary X-ray diffraction (XRD) patterns (Cu-Ka radiation) indicated a biphasic system subsisting almost to the plateau region, when a single-phase, layered material of inter- layer spacing, dOo2,17.698, (dOo4=8.86 A) is observed (Fig. 2). The use of isopentyl alcohol for hydrolytic polycondensation of APTEOS, leads to an increase in the interlayer distance: dOo2= 18.34(dOo49.19 A). This expansion is in complete agree- I""""""""""""""""""" 4 13 22 31 40 2e/o Fig. 2 Variation of the do,, diffraction in (a) ZrH,,,(PO,), [H2N(CHJ3SiO1J8 (b)as (a),after thermal processing at 500 "C ment with that expected for the insertion of a cubic octamer of calculated dimension, including the organic groups, of 11.2A.' Furthermore, the nature of the organic side-arms is such that, for each of the two cube faces (each of surface area CQ.125 A2)lying closest or parallel to the [Zr(HPO,),], layers, proton transfer will occur from four active -POH sites (of total surface area ca. 96A2), thus rationalising the maximal [Si] :[PI ratio observed (0.79),and corroborating the intercal- ation of siloxane as octameric units. Characteristic fingerprints of the organic groups were observed in IR.1 The layered structure of these materials was retained after calcination, to remove the organic functional groups, at various temperatures.XRD indicated a progressive decrease in interlayer distance: doo2(360"C)= 14.9 A; doo2(500"C)= 12.5 A (Fig. 2), and IR the absence of organic matter, con- firmed also by C, H, N analysis. Washing the calcined phases with a solution 1 mol dm-3 in HCl did not alter the XRD. An identical experimental protocol was observed for TIP and SnP and, for the former, similar results to those described above for ZrP were obtained. However, intercalation of [H2N(CH2)3SiOl.5]8 into TIP could apparently only be achieved when isopentyl alcohol was used in the preparation of the siloxane octamer for [Si]/[Ti] >2. XRD patterns reflected a generally lower degree of crystallinity than that observed for ZrP derivatives, and indicated a basal spacing of 18.04 A (dOo4=9.91A), falling to 12.06 A after calcination in air at 440 "C.In contrast, the results obtained for SnP show some marked differences, in particular, dependence (i) of the extent of intercalation on the contact time, and (ii) on the [Si]:[Sn] ratio, even above R=2, not observed for ZrP or Tip. Thus, after 2 days stirring, SnP derivatives are characterised by an increasingly well defined diffraction line progressively dis- placed to lower angles at higher ratios (R=0.82, dOo2= 18.03; R = 1.14,dOo2= 18.57;R =1.63,dOo2= 19.88 A), and an increase in the extent of the reaction, as estimated from the area of the SnP fingerprint, doo2=7.8 A. When the ratio is further increased, different intercalation behaviour is observed, which may be related to the different surface acidity characteristics of ZrP and SnP, or to the more marked propensity of the latter to hydrolysis. Thus when R= 2, XRD shows the coexistence of two expanded phases, the minor component of which corresponds to that observed previously for R= 1.6 and less, and the major having an interlayer distance of 26.90A (dOo4= 13.42,dOo6=8.98 A).This latter phase is the only one present at R =3. The coexistence of two phases when R=2 would seem to indicate that the evolution from a single to a double layer of [H2N(CH2)3SiOlJ8, within the interlayer region, is probably a discontinuous phase transition. Bilayer formation in pre- pillar materials was also reported in the +-SnP[A104A1,2(0H)2,(OH2)12]7 system., Elimination of organic matter from the fully expanded intercalate at 460 "C leads to materials having a well defined dOo2diffraction line, and an interlayer distance of 17.95 A (Fig.3) clearly indicating that the double layer is conserved on calcination. Although the precursor phases to silica crosslinked phos- phate materials are characterised by a maximum occupation of the active sites of ca. 80%, the specific surface area of ZrP-derived compounds after calcination is only slightly increased with respect to the starting metal phosphate,§ and these 1Recorded on a BOMEM DA8 spectrometer p(CH,) 710, 6(CH,) 1472,6,(NHi) 1542, Gas(NHl)1600 cm-'. v(Si-0) and v(Si-C) are masked by stretching vibrations of the PO,.group (950-1250 cm-') as are the corresponding deformation vibrations.6 Flowsorb 11 2300 instrument. N, adsorption-desorption at 77 K, after initial degassing of the samples at 200 "C, gave specific surface areas of M'"(HPO4),-H20, 5-10 m2 g-'; M1VHo.4(P04)2(Si01 .6,J1 MIV=Ti, Zr maximum 30 m2 g-'. J. MATER. CHEM., 1991, VOL. 1 v ulfill~~~~~1(L~1~~I~~I~.I~1I ~.~~ 3 12 21 30 39 201" Fig. 3 Effect of temperature on the interlayer distance in bilayered [H,N(CH,),SiO, J,-SnP (a) 25 (b) 380 (c)460 "C materials cannot, therefore, be considered as porous solids. In a recent report, however, intercalation from an aqueous solution containing a mixture of NH2(CH2)3Si(OH)3 mono-mers, and the corresponding dimeric and trimeric units, into ZrP was reported (using a significantly higher [Si] :[Zr] ratio), and porosity, based on the adsorption of hexane, was claimed." In contrast, the 'double-pillared' SnP-derived phases, obtained after calcination at 540 "C under vacuum, are characterised by a specific surface area of ca.230 m2 g-'. This observation can be rationalised in terms of partial hydrolysis of SnP during the intercalation reaction, which randomly deactivates certain -POH sites, so preventing their interaction with [H2N(CH2)$i01 .&. The almost identical uptake of the latter by ZrP as by SnP then requires an alternative arrangement of octamers in the interlayer region (the observed double-layer) which produces a porous struc- ture, unlike that of the crosslinked ZrP material.References 1 Pillared Layered Structures: Current Trends and Applications, ed. I. V. Mitchell, Elsevier Applied Science, London, 1990. 2 G. Alberti, U. Costantino, F. Marmottini, R. Vivani and P. Zappelli, in Pillared Layered Structures: Current Trends and Applications, ed. I. V. Mitchell, Elsevier Applied Science, London, 1990, p. 119. 3 A. Clearfield and B. D. Roberts, Inorg. Chem., 1988, 27, 3237; D. J. MacLachlan and D. M. Bibby, J. Chem. SOC., Dalton Trans., 1989, 895. 4 P. Maireles-Torres, P. Olivera-Pastor, E. Rodriguez-Castellon, A. Jimenez-Lopez, L. Alagna and A. A. G. Tomlinson, J. Mater. Chem., 1991, 1, 319. 5 P. Maireles-Torres, P. Olivera-Pastor, E. Rodriguez-Castellon, A. Jimenez-Lopez and A. A. G. Tomlinson, J. Mater. Chem., 1991, 1, 739. 6 R. M. Lewis, R. A. van Santen and K. C. Ott, Eur. Pat., 0159756 BI, 1985. 7 M. G. Voronkov, V. I. Lavrent'yev, Top. Curr. Chem., 1982, 102, 199. 8 W. E. Rudzinski, T. L. Montgomery, J. S. Frye, B. L. Hawkins and G. E. Maciel, J. Chromatogr., 1985, 323,281. 9 G. Alberti and E. Torraca, J. Znorg. Nucl. Chem., 1968, 30, 317; E. Kobayashi, Bull. Chem. SOC. Jpn., 1975,48,3114; E. Rodriguez- Castellon, A. Rodriguez-Garcia and S. Bruque, Znorg. Chem., 1985, 24, 1187. 10 L. Li, X. Liu, Y. Ge, L. Li and J. Klinowski, J. Phys. Chem., 1991,95, 5910. Communication 1/04196G; Received 12th August, 1991