DOI: 10.1002/asia.201000664

Organic–Inorganic Hybrid Saponites Obtained by Intercalation of Titano-Silsesquioxane

Fabio Carniato,[a] Chiara Bisio,*[a, b] Giorgio Gatti,[a] Matteo Guidotti,*[b]

Laura Sordelli,[b] and Leonardo Marchese[a]

Introduction

Polyhedral oligomeric silsesquioxanes (POSS) are a class ofcondensed three-dimensional oligomeric organosilica com-pounds, which have attracted over the last few years largeinterest in materials science and catalysis. These molecularmaterials, with general formula R8Si8O12, have each siliconatom bonded to 1.5 oxygen units (sesqui-) and a hydrocar-bon (-ane), leading to (RSiO1.5) bond units.[1–3]

Open-corner POSS compounds with uncondensed silanols(general formula R7Si7O9(OH)3) are currently far more in-teresting than fully condensed cubic R8Si8O12 silsesquiox-anes, owing to their facile functionalization with metal cen-ters. This leads to the formation of metal-containing silses-quioxanes (M-POSS), which are relevant as building blocksfor multifunctional composite materials or as model systemsfor heterogeneous catalysts.[4–7] M-POSS compounds, for ex-ample, have been dispersed on different silicas and polymer-ic matrices for the preparation of active catalysts in epoxida-

tion,[8–9] polymerization,[10–11] and oxidative dehydrogenationof olefins.[12–15]

Completely condensed POSS, however, are interesting fortheir use as cheap reactants for the preparation, throughcleavage and corner-capping reactions,[6,16] of M-POSS con-taining both metal centers and reactive organic functionali-ties, which can be designed to be bound to inorganic orpolymeric matrices. The intercalation of completely con-densed POSS in the interlayer space of clays (i.e. montmor-illonite) has led to the preparation of hybrid solids that havebeen successfully used as additives for the preparation ofpolymer nanocomposites with improved thermal stabili-ty.[17–18]

Recently, a novel hybrid material (named Ti-NHM-1)with improved thermal properties was prepared in our labo-ratories by the insertion of a novel functionalized M-POSS(Ti-NH2POSS)[19] in a synthetic Na saponite. Its applicationas nanofiller for polystyrene matrix was suggested.[20] Ti-NH2POSS is a versatile silsesquioxane[19] with a molecularstructure containing two functionalities: a titanium metalcenter, which may display catalytic properties when dis-persed or anchored on different silica materials[21] and/orpolymeric supports,[22,23] and a functional amino group suita-ble for the intercalation in clay-like solids (Figure 1). The in-sertion of Ti-containing aminopropylisobutyl-POSS (Ti-NH2POSS), previously described in the literature, within theinterlayer space of a protonic synthetic saponite clay (H-SAP) is described here, and the final material was namedTi-NHM-2. A detailed comparison of the structural, spectro-scopic, and thermal properties of both hybrid materials (Ti-

Abstract: The synthesis and characteri-zation of two bifunctional compositematerials based on synthetic saponiteclays is here presented. These materialswere prepared by intercalation of a Ti-containing aminopropylisobutyl poly-hedral oligomeric silsesquioxane (Ti-NH2POSS) in synthetic saponite sam-

ples containing interlayer sodium (Na-SAP) or protons (H-SAP). Hybrid or-ganic–inorganic materials, Ti-NHM-1

and Ti-NHM-2, were obtained uponion exchange. Structural, spectroscopic,and thermal properties of both hybridmaterials were investigated in detailalong with their catalytic activity in cy-clohexene oxidation.

Keywords: clays · organic–inor-ganic hybrids · saponites · silses-quioxanes · titanium

[a] Dr. F. Carniato, Dr. C. Bisio, Dr. G. Gatti, Prof. L. MarcheseDipartimento di Scienze e Tecnologie Avanzate and Nano-SISTEMIInterdisciplinary CentreUniversit� del Piemonte Orientale “A. Avogadro”Address V. Teresa Michel, 11, 15121 Alessandria (Italy)Fax: (+39) 0131360250E-mail : chiara.bisio@mfn.unipmn.it

[b] Dr. C. Bisio, Dr. M. Guidotti, Dr. L. SordelliISTM-CNR Istituto di Scienze e Tecnologie MolecolariVia G. Venezian, 21 Milano (Italy)

914 � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Asian J. 2011, 6, 914 – 921

FULL PAPERS

NHM-1 and Ti-NHM-2) was then carried out by FTIR, DRUV/Vis, X-ray diffraction (XRD), transmission electron mi-croscopy (TEM), and thermogravimetric analysis (TGA/DTG).

Proper tuning of the surface properties of the syntheticsaponite clays (i.e., the introduction of Brønsted acid sites)can lead to the preparation of innovative hybrid materials.The copresence of two structurally and functionally differentmoieties, that is, protonated Ti-NH3POSS and synthetic clay,may render the hybrid materials suitable for innovative ap-plications in catalysis and polymer science. Ti-NH2POSS

was inserted by ion exchange under acid conditions (i.e.,NH3

+ groups are present in the POSS compound) into thesynthetic Na saponite (Na-SAP) and H saponite (H-SAP),[24] prepared in our lab,[25] in order to obtain the finalhybrid materials, Ti-NHM-1 and Ti-NHM-2, respectively. Inaddition, investigation on the accessibility of the titaniumsites in both hybrid solids was carried out in the cyclohexeneepoxidation reaction.

Results and Discussion

Table 1 shows the Na and Ti content of the Ti-NHM-1 andTi-NHM-2 hybrid samples in comparison to the parent sap-onite solids (Na-SAP and H-SAP, respectively). As a result

of the ion exchange in acid medium, more than 90 % of theNa+ ions (Table 1) were replaced by protons. As recentlyshown, after the acid activation, saponite samples containtwo families of Brønsted acid sites with medium and highacidity.[25] As far as the Ti-NH3POSS/Na-SAP (Ti-NHM-1)[20] hybrid material is concerned, the exchange procedureresulted in a drastic decrease of sodium content (from 0.45to 0.04 mmol g�1) suggesting that more than 90 % of Na+

ions located in the interlamellar space of the saponite struc-ture were replaced by protonated Ti-NH3POSS ions. Materi-als with different Ti content were obtained depending onthe type of saponite used for the exchange procedure (i.e. ,Na-SAP or H-SAP). In particular, Ti-NHM-1 sample con-tained 0.44 mmol g�1 of Ti, whereas when H-SAP was usedas starting material, the estimated Ti content was only0.22 mmol g�1. This is probably associated with the fact thatthe exchange procedure of H+ , as it generally occurs in zeo-lites, is more difficult than the substitution of sodium ions. Itis worth noting that a bifunctional (acid and redox) system,Ti-NHM-2, was prepared following this procedure.

The XRD pattern of Na-SAP sample (Figure 2 A,curve a) was characterized by three main reflections cen-tered at 7.58 (d spacing of 11.7 �), 19.48 (4.57 �), and 60.582q (1.53 �), owing to the (001), (110), and (060) planes ofthe layered saponite. In particular, the presence of the (060)reflection suggests that the material has a trioctahedralstructure, as expected for saponite clay.[26] The basal (001)reflections of the two saponites were not well defined, ac-cording to a lack of homogeneous organization of the lamel-lae in both solids.[24,25] The acid treatment did not modifythe layered saponite structure, as evidenced by the fact thatall peaks characteristic of the clay structure remained unal-tered upon acid treatment (Figure 2 B, curve a).

Abstract in Italian: In questo lavoro sono descritte la sintesie la caratterizzazione di due materiali compositi bifunzionalia base di saponiti sintetiche. Tali materiali sono stati prepa-rati tramite intercalazione di Ti-aminopropilisobutilPOSS(Ti-NH2POSS) in saponiti sintetiche contenenti nello spaziointerlamellare ioni sodio (Na-SAP) o protoni (H-SAP). Talimateriali compositi ibridi organici/inorganici, denominati ri-spettivamente Ti-NHM-1 e Ti-NHM-2, sono stati sintetizzatitramite reazioni di scambio ionico. Sono state studiate indettaglio sia le propriet� strutturali, spettroscopiche e termi-che di tali ibridi, che la loro attivit� catalitica per l’ossidazio-ne del cicloesene.

Figure 1. Optimized structure of Ti-NH2POSS in protonated form.

Table 1. Na and Ti content (mmol g�1) in synthetic H-SAP, Na-SAP, andderived hybrid materials Ti-NHM-2 and Ti-NHM-1.

Na-SAP H-SAP Ti-NHM-1 Ti-NHM-2

Na 0.45 0.03 0.04 0.01Ti – – 0.44 0.22

Chem. Asian J. 2011, 6, 914 – 921 � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemasianj.org 915

Similarly, the ion exchange procedure used to intercalateTi-NH3POSS in both Na-SAP and H-SAP did not affect sig-nificantly their layered structure, and only a modification ofthe interlayer space was found. Besides the signals around7.58 2q, already found in the parent Na-SAP and H-SAPsamples, the XRD patterns of Ti-NHM-1 (Figure 2 A, b)and Ti-NHM-2 (Figure 2 B, b) were characterized by thepresence of signals centered at 3.08 and 4.08 2q, which areassociated with an interlayer distance of 30 and 22 �, re-spectively. These data indicated that the interlayer distanceof both saponite samples was increased upon ion exchange,suggesting the occurrence of Ti-NH3POSS intercalation inthe layered solids.

HRTEM images of Ti-NHM-1 (Figure 3 A) and Ti-NHM-2 (Figure 3 B) indicated that after the ion exchange proce-dure the samples maintained lamellar morphology,[25] andthat the interlayer space of both samples was increased as aconsequence of the introduction of Ti-NH3POSS. Ti-NHM-1showed regions with larger interlayer space (from 15 to30 �) than pristine saponite (from 11 to 12 �). The hetero-geneity of the composite system was determined by measur-ing the interlayer distance of more than a hundred crystals.A wide d-spacing distribution (see the histogram of Fig-

ure 3 AI) was found, thus suggesting that Ti-NH3POSS mole-cules are arranged in different spatial configurations withinthe saponite layers. A more homogeneous d-spacing distri-bution was observed in the case of Ti-NHM-2 (Figures 3 Band 3 BI). Besides the d spacing of the pristine material, infact, two sets of interlayer distances centered at 11 � (typi-cal of pristine material) and in the range from 22 to 24 �were found for this sample (Figure 3 BI). This is probablydue to the lower loading of Ti-NH3-POSS in comparison tothe composite prepared by using Na-SAP and probably to adifferent organization of the POSS units inside the claychannels. EDX analysis performed on the intercalatedsample indicated the presence of Ti atoms in the interlayerregion of the clay (data not shown for the sake of brevity).

Ti-NHM-1 and Ti-NHM-2 hybrid materials were alsostudied by IR spectroscopy (Figure 4). The IR spectrum ofNa-SAP and H-SAP (Figure 4, A and B, curves a) showed asharp peak at 3675 cm�1, owing to the OH stretching modeof structural Mg(OH)2 groups in the octahedral layers of thesaponite structure,[27, 28] accompanied by a broad band in therange from 3600 to 3000 cm�1, owing to the OH stretchingmode of adsorbed water molecules, whose presence was alsoindicated by the bending mode at 1640 cm�1. At lower fre-quencies, a strong absorption at about 1018 cm�1 relative tothe Si-O-Si stretching mode of the silicate structure wasfound, along with bands at 675 and 450 cm�1 owing to thebending mode of the Mg-OH and Si-O-Si groups, respec-tively.[28]

From the comparison between the IR spectra of pristinesaponite samples and the hybrid materials, it was found thatthe introduction of Ti-NH3POSS in the matrix led to a sig-nificant decrease of water content, as derived from thelower intensity of the bands owing to stretching and bendingmodes of adsorbed water in the range from 3600 to 3000and 1640 cm�1, respectively (Figure 4, A and B, curves b).

Figure 2. XRD pattern of A) Na-SAP (a) and Ti-NHM-1 (b); B) H-SAP(a) and Ti-NHM-2 (b). The X-ray diffractogram at low angles of Ti-NHM-2 is displayed in the inset of frame (B).

Figure 3. High-magnification HRTEM micrographs of A) Ti-NHM-1 andB) Ti-NHM-2; the histograms of the d-spacing distribution of both sam-ples are displayed in frames AI and BI, respectively. np%= relative per-centage of the number of particles.

916 www.chemasianj.org � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Asian J. 2011, 6, 914 – 921

FULL PAPERSC. Bisio, M. Guidotti et al.

Besides the absorptions typical of an inorganic clay frame-work, the IR spectra of Ti-NHM-1 and Ti-NHM-2 showedbands of protonated Ti-NH3POSS molecules. The IR spec-trum of the molecular compound (Figure 4, A and B, cur-ves c) displayed, in fact, several peaks in the range from2950 to 2800 cm�1, which are due to C�H stretching vibra-tions of the POSS isobutyl chains, the bending modes fallingin the range from 1470 to 1200 cm�1. Moreover, two bandsat about 1610 and 1520 cm�1, assigned respectively to theout-of-phase and in-phase deformations of NH3

+ group,were detected (see inset in Figure 4, A and B). The relativeintensity of bands typical of Ti-NH3POSS in Na-SAP andH-SAP samples suggested that the two clays contain a dif-ferent amount of POSS, in agreement with chemical analysis(see above) and with TGA results (see below).

The thermal properties of both pristine saponites andhybrid materials were investigated by thermogravimetricanalysis. The TGA results of Ti-NHM-1 and Ti-NHM-2 arereported in Figure 5. Both Ti-NHM-1 (Figure 5 A, curve b)

and Ti-NHM-2 (Figure 5 AI, curve b) contained a loweramount of adsorbed water molecules with respect to puresaponite samples (Figure 5, A and AI, curves a, respective-ly), as witnessed by the smaller weight losses at about100 8C. This behavior indicated that the introduction of Ti-NH3POSS modifies the hydrophilic character of the clay sur-face.

TGA results suggest that the intercalation of Ti-NH3POSS in both saponite materials resulted in a significantmodification of the thermal degradation pathways of POSSmolecules. Interestingly, both hybrid samples showed ther-mal decomposition of the organic chains of Ti-NH3POSS athigher temperature (above 400 8C) than pure Ti-NH2POSS(around 300 8C),[20] thus indicating that when intercalatedwithin the saponite interlayer space, the degradation wassignificantly delayed with respect to pure Ti-NH2POSS. Thisbehavior can be associated to the fact that the clay structureplays an active role in stabilizing and protecting Ti-NH3POSS molecules by increasing their thermal stability.On the other hand, the observed behavior is clear-cut evi-dence that Ti-NH3POSS molecules are intercalated withinthe saponite interlayer space, thus indicating that moleculesphysically adsorbed on the surface of the clay are negligible.

Nevertheless, the thermal stability of the hybrid materialsappeared significantly affected by the chemical nature of theclay. In fact, the onset degradation temperature of Ti-NHM-2 (ca. 270 8C, Figure 5 BI, curve b) resulted as anticipatedwith respect to the case of Ti-NHM-1 (ca. 310 8C, Figure 5 B,curve b). In addition, the thermal profile of Ti-NHM-1 (Fig-ure 5 A, curve b) showed a weight loss of about 10 wt % be-tween 500 and 750 8C, which can be due to the formation ofcharring products during the degradation of the Ti-NH3POSS organic chains.[20] Ti-NHM-2 did not show a sig-nificant weight loss in the range from 500 to 750 8C (Fig-ure 5 AI, curve b). This can be ascribed to the presence of a

Figure 5. Thermogravimetric analysis performed under argon flow of Na-SAP (panel A, curve a), Ti-NHM-1 (panel A, curve b), H-SAP (panel AI,curve a), and Ti-NHM-2 (panel AI, curve b). The derivative curves(DTG) are displayed in frames B and BI.

Figure 4. IR spectra of A) Na-SAP (a), Ti-NHM-1 (b), and Ti-NH3POSSprotonated in HCl solution (c); B) H-SAP (a), Ti-NHM-2 (b), and Ti-NH3POSS protonated in HCl solution (c). The IR spectra of the samplein the range from 1700 to 1300 cm�1 are reported in the insets.

Chem. Asian J. 2011, 6, 914 – 921 � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemasianj.org 917

Organic–Inorganic Hybrid Saponites

significant amount of acid sites in Ti-NHM-2 (see elementalanalysis) that promote cracking reactions of Ti-NH3POSSresidues, which are thus decomposed without formation ofcondensed phases. This suggested that the decomposition ofTi-NH3POSS occurred with a different mechanism when themolecular complex is intercalated in the protonic or sodicform of the saponite clays.

The coordination and oxidation state of the Ti centers inTi-NH2POSS and in both Ti-NHM-1 and Ti-NHM-2 hybridmaterials have been studied by DR UV/Vis spectroscopy(Figure 6). The DR UV/Vis spectrum of Ti-NH2POSS

(Figure 6, curve a), showed a main absorption at 240 nm, as-signed to the charge-transfer transition between oxygenatoms and the TiIV center in tetrahedral coordination, whichis typical of Ti-POSS compounds with monomer struc-ture.[13, 14,19] The DR UV/Vis spectrum of Ti-NHM-2 collect-ed after evacuating the sample at room temperature(Figure 6, curve b) is very similar to that of Ti-NH2POSS,suggesting that the coordination of titanium was preservedduring the intercalation in pro-tonic saponite.

The introduction of Ti-NH3POSS in the Na-SAPsample, however, significantlymodified the Ti coordination, assuggested by the DR UV/Visspectrum of this intercalatedcompound (Figure 6, curve c).Besides an absorption at ca.245 nm, a strong shoulder at ca.290 nm was also found(Figure 6, curve c), which is as-signed to pentacoordinated Tiin dimeric form,[29] thus suggest-ing that Ti-NH3POSS moleculesform aggregates during interca-lation in Na-SAP. This phenom-enon is probably associatedwith the fact that a higher Ti-NH3POSS loading is attained

when the compound is introduced in the sodic form of sap-onite, according to the elemental analysis.

In agreement with structural and spectroscopic results, aschematic representation of the interlayer space of Ti-NHM-2 material is proposed in Figure 7. Ti-NH3POSS mon-omers should be present within the saponite interlayer gal-leries for its average d spacing is 24 � (histogram of Fig-ure 3 BI), and the thickness of a single clay layer of saponiteis about 7–8 �. Besides Ti-containing monomer units, pro-tons are present on the internal surface of Ti-NHM-2,making this hybrid material appealing for bifunctional acid/redox catalysis. A representation of Ti-NHM-1 is difficult asmonomers and dimers of unknown nature (UV bands at 245and 290 nm) are present in its interlayer space, and this is inaccordance with the fact that this hybrid material displays amore heterogeneous d-spacing distribution (see Figure 3 AI).

The liquid-phase epoxidation of cyclohexene to cyclohex-ene epoxide was chosen as a classical test reaction to assessthe activity of the titanium sites. Ti-NHM-1 and Ti-NHM-2were used as catalysts to verify whether the TiIV atoms inthe solids were accessible to the reactants and possessed cat-alytic activity. Both samples did not show any activity whentert-butyl hydroperoxide (TBHP) was employed as oxidant(Table 2), under the same conditions adopted with other

Figure 7. A schematic representation of TOT layers of Ti-NHM-2; frame-work Al ions serve as proton-exchange sites, that is, the loci of theBrønsted acidity.

Figure 6. DR UV/Vis spectra of Ti-NH2POSS (a), Ti-NHM-2 (b), and Ti-NHM-1 (c) diluted in BaSO4 matrix (10 wt %). Spectra were collectedafter evacuating the samples for 2 h at room temperature. K-M=Kubel-ka–Munk function.

Table 2. Liquid-phase epoxidation of cyclohexene over Ti-containing saponite samples.

Catalyst Oxidant Ti content[a] [wt %] Epoxide yield[%]

Epoxide selec-tivity [%]

TON[b] Main side products

3 h 24 h 3 h 24 h at 3 h

Ti-NHM-1 TBHP 1.98 n.d.[c] n.d. n.d. n.d. – 1-cyclohexylcyclohexene(traces)

Ti-NHM-1 H2O2 1.98 7 6 63 31 1.7 1,2-cyclohexanediol,2-cyclohexen-1-ol,

2-cyclohexen-1-oneTi-NHM-2 TBHP 1.02 n.d. n.d. n.d. n.d. – 1-cyclohexylcyclohexene

(traces)Ti-NHM-2 H2O2 1.02 6 10 51 39 2.8 dicarboxylic acids,

2-cyclohexen-1-ol,2-cyclohexen-1-one

H-Sap H2O2 – n.d. n.d. n.d. n.d. – 1-cyclohexylcydohexenenone H2O2 – n.d. n.d. n.d. n.d. – –

Ti-SBA-15 H2O2 1.46 30 29 59 65 9.9 1,2-cyclohexanediol,2-cyclohexen-1-ol,

2-cyclohexen-1-one

Reaction conditions: 100 mg catalyst, 2.5 mmol cyclohexene, 0.5 mmol oxidant: H2O2 (aq. 30 wt %) or TBHP(5.5 m in dry decane), solvent acetonitrile; 85 8C; 3 h. [a] determined by ICP-AES elemental analysis; [b] Turn-Over Number (moles of produced epoxide per mole of titanium); [c] not detectable.

918 www.chemasianj.org � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Asian J. 2011, 6, 914 – 921

FULL PAPERSC. Bisio, M. Guidotti et al.

widely studied titanium-containing silicate materials.[30,31]

With TBHP, no formation of epoxide was detected and theconversion of cyclohexene was negligible. The solids wereactive, on the contrary, in the presence of aqueous hydrogenperoxide and, in this case, the formation of cyclohexene ep-oxide was recorded as the main product. Such behavior is afurther confirmation that Ti centers are located in the inter-layer spaces and are reachable only by small and stericallyunencumbered oxidants. Actually, the formation of cyclo-hexene epoxide was low in both hybrid materials (around6 % for Ti-NHM-1 and 10 % for Ti-NHM-2), but noteworthyif one considers that, under the same conditions, a maximumepoxide yield of about 30 % is obtained over the highly ac-cessible Ti-SBA-15 mesoporous silica.

No epoxide formation was detected without catalyst (thatis, no epoxide resulting from noncatalyzed auto-oxidation)or with the saponite material without titanium (that is, noactivity owing to the sole action of the acid matrix). Thus,the presence of titanium in the catalysts is essential for ep-oxide formation. For the same reason, the in situ formationof peroxoimidic acid (owing to the copresence of acetoni-trile and H2O2 via Payne-type reactions) as an active oxidiz-ing species can be excluded.

In terms of selectivity, Ti-NHM-1 and Ti-NHM-2 solidsshowed a selectivity toward epoxide after 3 h that was com-parable to that of Ti-SBA-15, and about 40 % of the ob-served secondary products were due to allylic oxidation to2-cyclohexen-1-ol and 2-cyclohexen-1-one. Such compoundsare formed by free-radical homolytic attack by H2O2.

[32,33] Inaddition, the unselective formation of epoxide cleavageproducts (short-chain dicarboxylic acids) was detected overTi-NHM-2 in minor, but non-negligible, amounts. Thismeans that the copresence of acid sites (H+) in the interlay-er space can promote the cleavage of the epoxidized cycloal-kene.

These results, obtained using a model reaction, demon-strate that: 1) titanium atoms in Ti-NHM-1 and Ti-NHM-2are accessible to small reactants and have coordination sitesthat are available for interaction with oxidizing species andsuitable for redox reactions, despite the different organiza-tion of Ti-NH3POSS molecules in the protonic and sodicclays, and 2) protonic acid centers in Ti-NHM-2 are avail-able in the catalyst and can be exploited for acid-catalyzedreactions. By an appropriate choice of the reactants and ofthe catalytic reaction, Ti-NHM-2 could be thus used as acatalyst for reactions where redox and acid-catalyzed stepsare simultaneously required over substrates of medium size.

Conclusions

A titano-silsesquioxane bearing in the same molecular struc-ture a functional organic group (-NH3

+) and a metal center(TiIV) was intercalated into two synthetic saponite clays con-taining sodium and H+ , respectively. XRD and HRTEMclearly showed that organomodified synthetic clays with dif-ferent degrees of Ti-NH3POSS intercalation were produced.

Different arrangements of Ti-NH3POSS molecules in thesaponite interlayer space were suggested.

DR UV/Vis data showed that the tetrahedral coordinationof titanium centers of Ti-NH3POSS were preserved duringthe intercalation into H-SAP, while it was drastically modi-fied in the case of the Ti-NHM-1 hybrid material, where ag-gregation of molecular complexes occurred. It is relevant tounderline that the embedding of Ti-NH3POSS in saponiteclays leads to a remarkable thermal stabilization of the mo-lecular compound and that, depending on the chemicalnature of the clay interlayer, hybrid materials with signifi-cantly different chemical properties can be prepared.

The catalytic dehydrogenation performances of Ti-NH3POSS embedded in sodium saponite (Ti-NHM-1)should be exploited for applications in polymer science, forexample, in the preparation of polymer composites with en-hanced thermal properties, which have already been report-ed in the literature in the case of composite material basedon polystyrene.[20] In this case, the catalytic activity of Ticenters in combination with the physical barrier effects of-fered by the clay should be relevant for the formation ofcharring products, which have flame-retardant effects,during combustion. Furthermore, the intercalation of Ti-NH3POSS into protonic acid saponite leads to a bifunctionalTi-NHM-2 material which may be used as a heterogeneouscatalyst in which acid sites and isolated metal redox-activecenters are simultaneously present and necessary for two-step bifunctional catalysis.

Experimental Section

Materials Preparation

Ti-NH2POSS: Ti-aminopropyl-isobutyl POSS (Ti-NH2POSS) was pre-pared following the procedeure reported in the literature.[19]

Na-SAP and H-SAP: Synthetic saponite clays were prepared by hydro-thermal synthesis of a gel formed by mixing Al ACHTUNGTRENNUNG[OCH ACHTUNGTRENNUNG(CH3)2]3, NaOH,Mg ACHTUNGTRENNUNG(CH3COO)2, SiO2, and H2O (with a gel composition of 1 SiO2; 0.834Mg ACHTUNGTRENNUNG(CH3CO2)2; 0.113 Al ACHTUNGTRENNUNG[OCH ACHTUNGTRENNUNG(CH3)2]3; 0.113 NaOH; 18.6 H2O) and ex-changed by Na+ (in the case of Na-SAP sample) and H+ ions (H-SAP)according to procedures already described in the literature[22–23] and opti-mized in our laboratories.[21, 24] The measured cation exchange capacity(CEC) of the produced solids was 59.7 meq/100 g.[25, 26] Synthetic saponiteclays were prepared by hydrothermal synthesis of a gel formed by mixingAl ACHTUNGTRENNUNG[OCH ACHTUNGTRENNUNG(CH3)2]3, NaOH, Mg ACHTUNGTRENNUNG(CH3COO)2, SiO2, and H2O (with a gelcomposition of 1 SiO2; 0.834 Mg ACHTUNGTRENNUNG(CH3CO2)2; 0.113 Al ACHTUNGTRENNUNG[OCH ACHTUNGTRENNUNG(CH3)2]3;0.113 NaOH; 18.6 H2O) and exchanged by Na+ and H+ ions, according toprocedures already described in the literature[34, 35] and optimized in ourlaboratories.[24, 25]

Intercalation of Ti-NH2POSS in Na-SAP and H-SAP: Suspensions ofboth Na-SAP and H-SAP were prepared by adding 1 g of powders to50 mL deionized water and stirred for 4 h. In parallel, Ti-NH2POSS(0.538 g) was mixed with 5 mL THF (Sigma Aldrich) and 2 mL HCl(10 %) for 1 h, adapting the procedure reported in literature,[24] to form(Ti-NH3POSS)Cl. Finally, the solution containing (Ti-NH3POSS)Cl andthe clay suspensions were mixed under stirring at 50 8C for 24 h, whichled to Ti-NH3POSS/Na-SAP and Ti-NH3POSS/H-SAP composite materi-als, named Ti-NHM-1 and Ti-NHM-2, respectively. Subsequently, theproducts were filtered and washed several times with water and dried inan oven at 80 8C.

Chem. Asian J. 2011, 6, 914 – 921 � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemasianj.org 919

Organic–Inorganic Hybrid Saponites

Characterization Techniques

The chemical composition of pristine clay and hybrid material (Ti-NHM-1 and Ti-NHM-2) were determined with inductively coupled plasma massspectrometry (ICP-MS) and atomic absorption spectroscopy (AAS) byITECON laboratory (Nizza Monferrato, Italy). The cationic exchange ca-pacity (CEC) of the synthesized materials was determined by the methodreported in the literature.[25] Infrared spectra of solid samples in KBr pel-lets were collected using a Bruker Equinox 55 spectrometer (resolutionof 4 cm�1). Variable-temperature IR analyses were performed on anFTIR Nicolet 5700 spectrometer (Thermo Optics) using a resolution of4 cm�1. The samples were pressed in the form of self-supporting wafersand placed into an IR cell equipped with KBr windows permanently at-tached to high-vacuum line (residual pressure: 1.0� 10�6 Torr). TGAanalyses were performed on a Setaram SETSYS Evolution instrumentunder argon (gas flow 20 mL min�1); samples were heated up to 800 8Cwith a rate of 10 8C min�1. X-ray diffraction (XRD) patterns were ob-tained on a ARL XTRA48 diffractometer using CuKa radiation (l=

1.54062 �). HRTEM images were collected on a JEOL 3010 high-resolu-tion transmission electron microscope operating at 300 kV. Specimenswere prepared by dispersing the sample by sonication in isopropanol andby depositing a few drops of the suspension on carbon-coated grids. Themicroscope was equipped with an Oxford Instruments INCA TEM 200system for energy-dispersive X-ray (EDS) analysis. DR UV/Vis spectrawere recorded using a Perkin–Elmer Lambda 900 spectrometer equippedwith a diffuse reflectance sphere accessory (DR UV/Vis ). Prior the anal-ysis the samples were dispersed in anhydrous BaSO4 (10 wt %).

Ti-NH3POSS geometry was optimized by using the Gaussian 03 pack-age[36] at the BP86 level of theory[37, 38] using a pseudopotential ECPLANL2DZ basis set for the Ti atom;[39–41] for all other atoms the split-va-lence+ polarization basis set of Ahlrichs, denoted as SVP,[42] was used(polarization functions were also included on all the atoms of the ligand).The structure was fully optimized, without any constraints.

Catalytic Tests

The solids (100 mg) were pretreated at 150 8C under dry air for 1 h priorto use. Then, 2.5 mmol of cyclohexene (Aldrich) and 0.7 mmol of internalstandard (mesitylene; Fluka) were added to the catalyst in acetonitrile(5 mL; Riedel-de-Haen) under nitrogen. The oxidant (0.5 mmol) wasadded either dropwise (1.8 mL over 3 h; addition rate 0.01 mL min�1), asin the case of hydrogen peroxide (aq. 30 wt %, Aldrich), or in a one-ali-quot addition, as in the case of tert-butyl hydroperoxide (5.5 m in anhy-drous decane; Aldrich). The reaction mixture was analyzed at the end ofthe slow addition (after 3 h) and after 24 h by GC-FID and GC-MS. Tita-nium contents were obtained by ICP-AES elemental analysis. The refer-ence material Ti-SBA-15 was obtained by grafting titanocene dichlorideonto purely siliceous SBA-15 according to a grafting protocol elsewheredescribed.[43, 44]

Acknowledgements

The authors acknowledge financial support from MIUR (PRIN Project“Progettazione e sintesi di Silsesquiossani Poliedrici Multifunzionali perCompositi Polimerici Innovativi Termicamente Stabili” and Network“Rete Nazionale di Ricerca sulle Nanoscienze - ItalNanoNet”, protocolno. RBPR05JH2P) and from Regione Piemonte (Progetto NANOMAT,Docup 2000–2006, Linea 2.4a). They are also grateful to Ms. Elena Gavri-lova for catalytic epoxidation tests and Dr. Luca Bertinetti for HRTEManalysis.

[1] R. H. Baney, M. Itoh, A. Sakakibara, T. Suzuki, Chem. Rev. 1995,95, 1409 –1430.

[2] P. G. Harrison, J. Organomet. Chem. 1997, 542, 141 –183.[3] P. P. Pescarmona, T. Maschmeyer, Aust. J. Chem. 2001, 54, 583 –596.

[4] R. W. J. M. Hanssen, R. A. van Santen, H. C. L. Abbenhuis, Eur. J.Inorg. Chem. 2004, 675 – 683.

[5] F. J. Feher, J. F. Walzer, Inorg. Chem. 1991, 30, 1689 – 1694.[6] V. Lorenz, A. Fischer, S. Gießmann, J. W. Gilje, Y. Gun’ko, K.

Jacob, F. T. Edelmann, Coord. Chem. Rev. 2000, 206–207, 321 –368.[7] R. Duchateau, Chem. Rev. 2002, 102, 3525 – 3542.[8] P. P. Pescarmona, J. C. Van der Waal, I. E. Maxwell, T. Maschmeyer,

Angew. Chem. 2001, 113, 762 –765; Angew. Chem. Int. Ed. 2001, 40,740 – 743.

[9] P. Smet, J. Riondato, T. Pauwels, L. Moens, L. Verdonck, Inorg.Chem. Commun. 2000, 3, 557 –562.

[10] J. C. Liu, Chem. Commun. 1996, 1109 – 1110.[11] J. C. Liu, Appl. Organomet. Chem. 1999, 13, 295 – 302.[12] L. Zhang, H. C. L. Abbenhuis, G. Gerritsen, N. N. Bhriain,

P. C. M. M. Magusin, B. Mezari, W. Han, R. A. van Santen, Q. Yang,C. Li, Chem. Eur. J. 2007, 13, 1210 – 1221.

[13] F. Carniato, E. Boccaleri, L. Marchese, A. Fina, D. Tabuani, G.Camino, Eur. J. Inorg. Chem. 2007, 585 –591.

[14] A. Fina, H. C. L. Abbenhuis, D. Tabuani, A. Frache, G. Camino,Polym. Degrad. Stab. 2006, 91, 1064 –1070.

[15] A. Fina, H. C. L. Abbenhuis, D. Tabuani, G. Camino, Polym.Degrad. Stab. 2006, 91, 2275 – 2281.

[16] F. J. Feher, R. Terroba, J. W. Ziller, Chem. Commun. 1999, 2153 –2154.

[17] H. Liu, W. Zhang, S. Zheng, Polymer 2005, 46, 157 – 165.[18] D.-R. Yei, S.-W. Kuo, Y.-C. Su, F.-C. Chang, Polymer 2004, 45,

2633 – 2640.[19] F. Carniato, E. Boccaleri, L. Marchese, Dalton Trans. 2008, 36 –39.[20] F. Carniato, C. Bisio, G. Gatti, E. Boccaleri, L. Bertinetti, S. Coluc-

cia, O. Monticelli, L. Marchese, Angew. Chem. 2009, 121, 6175 –6177; Angew. Chem. Int. Ed. 2009, 48, 6059 –6061.

[21] F. Carniato, C. Bisio, E. Boccaleri, M. Guidotti, E. Gavrilova, L.Marchese, Chem. Eur. J. 2008, 14, 8098 –8101.

[22] F. Carniato, A. Fina, D. Tabuani, E. Boccaleri, Nanotechnology2008, 19, 475701.

[23] O. Monticelli, E. Zunino, F. Carniato, E. Boccaleri, L. Marchese, A.Chincarini, Polym. Adv. Technol. 2009, DOI: 10.1002/pat.1508.

[24] C. Bisio, G. Gatti, E. Boccaleri, L. Marchese, G. B. Superti, H. O.Pastore, M. Thommes, Microporous Mesoporous Mater. 2008, 107,90– 101.

[25] C. Bisio, G. Gatti, E. Boccaleri, L. Marchese, L. Bertinetti, S. Coluc-cia, Langmuir 2008, 24, 2808 – 2819.

[26] R. Prihod’ko, E. J. M. Hensen, M. Sychev, I. Stolyarova, T. E. Shubi-na, I. Astrelin, R. A. van Santen, Microporous Mesoporous Mater.2004, 69, 49–63.

[27] H. W. Van der Marel, H. Beutelspacher, Atlas of Infrared Spectros-copy of Clay Minerals and Their Admixtures, Elsevier, Amsterdam,1976, p. 191.

[28] J. T. Kloprogge, R. L. Frost, Vib. Spectrosc. 2000, 23, 119 –129.[29] E. Gianotti, A. Frache, S. Coluccia, J. M. Thomas, T. Maschmeyer,

L. Marchese, J. Mol. Catal. A 2003, 204–205, 483 – 489.[30] M. Guidotti, N. Ravasio, R. Psaro, G. Ferraris, G. Moretti, J. Catal.

2003, 214, 242 –250.[31] M. Guidotti, I. Batonneau-Gener, E. Gianotti, L. Marchese, S.

Mignard, R. Psaro, M. Sgobba, N. Ravasio, Microporous Mesopo-rous Mater. 2008, 111, 39 –47.

[32] J. M. Fraile, J. I. Garcia, J. A. Mayoral, E. Vispe, J. Catal. 2001, 204,146 – 156.

[33] M. Guidotti, C. Pirovano, N. Ravasio, B. L�zaro, J. M. Fraile, J. A.Mayoral, B. Coq, A. Galarneau, Green Chem. 2009, 11, 1421 –1427.

[34] J. T. Kloprogge, J. Breukelaar, J. B. H. Jansen, J. W. Geus, Clays ClayMiner. 1993, 41, 103 –110.

[35] J. T. Kloprogge, J. Breukelaar, J. W. Geus, J. B. H. Jansen, Clays ClayMiner. 1994, 42, 18 –22.

[36] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.

920 www.chemasianj.org � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Asian J. 2011, 6, 914 – 921

FULL PAPERSC. Bisio, M. Guidotti et al.

Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-ingford CT, 2004.

[37] A. Becke, Phys. Rev. A 1988, 38, 3098 –3100.[38] P. Perdew, Phys. Rev. B 1986, 33, 8822 – 8824.[39] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270 –283.[40] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 284 –298.[41] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299 –310.[42] A. Sch�fer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97, 2571 –

2577.[43] T. Maschmeyer, F. Rey, G. Sankar, J. M. Thomas, Nature 1995, 378,

159 – 162.[44] M. Guidotti, L. Conti, A. Fusi, N. Ravasio, R. Psaro, J. Mol. Catal.

A 2002, 182–183, 151 – 156.Received: September 14, 2010

Published online: November 30, 2010

Chem. Asian J. 2011, 6, 914 – 921 � 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemasianj.org 921

Organic–Inorganic Hybrid Saponites