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Tin Nanoparticles in Carbon/Silica Hybrid Materials by the Use of Twin Polymerization [ChemPlusChem]
[October 30, 2014]

Tin Nanoparticles in Carbon/Silica Hybrid Materials by the Use of Twin Polymerization [ChemPlusChem]


(ChemPlusChem Via Acquire Media NewsEdge) Simultaneous twin polymerization was used to synthesize hybrid materials composed of tin oxide, silica, and a phenolic resin starting from a mixture of 2,2'-spirobi[4H-1,3,2-benzodiox-asiline] (Si-spiro) with either the tin(IV) alkoxides 2,2'-spiro- bi[4H-1,3,2-benzodioxastannine] (A), 2,2'-spirobi[6-methyl-4H- 1,3,2-benzodioxastannine] (B), and 2,2'-spirobi[6-methoxy-4H- 1,3,2-benzodioxastannine] (C) or the novel tin(II) alkoxides tin(II)-2-(oxidomethyl)-4-methoxyphenolate (D) and tin(II)-2-(oxidomethyl)-5-methoxyphenolate (E). In addition, the twin polymerization of the twin monomer Si-spiro in the presence of tin-containing additives, such as Sn(OtBu)4, Sn(OnBu)2, Sn(OAc)4, and Sn(OAc)2, was investigated for comparison. The as-prepared hybrid materials were characterized using solid-state NMR spectroscopy (13 C, 29 Si, 119 Sn) and high-angle annular dark field scanning transmission electron microscopy, and were finally converted under Ar/H2 atmosphere at 600°C to tin nanoparticles (10-200 nm) in porous carbon/silica hybrid materials (Sn/C/SiO2) with BET surface areas up to 352 m2 g-1.



Keywords : alkoxides · nanoparticles · organic-inorganic hybrid materials · tin · twin polymerization In memory of Gerhard Cox Introduction The interest in nanostructured hybrid materials composed of homogeneously dispersed tin nanoparticles in a SiO2 matrix has grown rapidly in recent years. This is attributed to poten- tial applications in various fields such as semiconductors,[1-3] optoelectronics,[4-6] photovoltaics,[7] and anode materials for Li- ion batteries.[8, 9] For example, Hwang et al. reported recently the one-pot synthesis of tin embedded in carbon/silica hybrid materials starting from organotin compounds and demonstrat- ed the performance of such composites as anode materials for lithium-ion batteries.[10] This represents an interesting approach with regard to size control and homogeneous distribution of the embedded tin nanoparticles within the silica matrix. How- ever, organotin compounds such as those used in the study (tributylphenyltin or tributylstannane) should be avoided in future industrial applications because of their toxic nature.[11,12] Herein, a novel approach based on less toxic tin alkoxides and carboxylates is presented. Previously, the preparation of hybrid materials composed of tin oxide, silica, and a phenolic resin by the use of the simultaneous twin polymerization route starting from novel tin(IV) alkoxides was reported.[13] The special char- acter of this type of twin polymerization is the formation of three different materials in a coupled reaction sequence start- ing from two molecular precursors, here denoted as twin mon- omers.[14-20] The different materials are cross-linked in the hybrid material, which prevents phase separation and leads to bicontinuous networks with domain sizes of a few nanometers. Herein, an extension of this approach to prepare tin embed- ded in carbon/silica hybrid materials under reducing conditions is presented (Scheme 1).

In this process the SiO2 acts as a crystal growth inhibitor and prevents sintering of the tin nanoparticles even at tempera- tures well above the melting point of tin. Thus, uniformly dis- tributed tin nanoparticles in a carbon/silica matrix are made accessible. In addition to the previously reported tin(IV) alkox- ides,[13] tin(II) alkoxides as well as nonpolymerizable tin precur- sors (alkoxides and acetates) were probed as additives in the twin polymerization process.


Results and Discussion Hybrid materials prepared by the use of simultaneous twin polymerization The tin(IV) alkoxides A-C were synthesized and polymerized with the spirocyclic silicon monomer 2,2'-spirobi[4H-1,3,2-ben- zodioxasiline] (Si-spiro) in the melt to give the amorphous hybrid materials 1-3 composed of tin oxide, silica, and a phe- nolic resin according to a previously reported procedure (Fig- ure S1 in the Supporting Information).[13] In addition, we have synthesized the novel tin(II) alkoxides D and E to probe their potential for the simultaneous twin polymerization process (Scheme 2). The reduced number of organic ligands in the tin(II) precursors as compared to the tin(IV) alkoxides decreases the carbon content in the as-prepared hybrid materials and thus the tin content should increase in the final material. Si- multaneous twin polymerization of the tin(II) precursors D and E together with Si-spiro either in the melt or in solution gave the corresponding hybrid materials 4 and 5. Solid-state 13C NMR spectra show the expected signals, which are as- signed to the phenolic resin with ortho/ortho' and ortho/para' substitution (Figure S2).[21] An additional broad 13C NMR signal at about d =70 ppm and the 29Si NMR spectra with signals in the range d = 92-105 ppm are indicative of some incompletely reacted silicon precursors and/or incompletely condensed silica moieties (Figure S3). Similar observations were made previous- ly for the twin polymerization of several derivatives of Si- spiro.[22] The hybrid materials 4 and 5 both show the typical mor- phology of twin polymers with 1-2 nm sized domains as dem- onstrated by the high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images (Figure 1).[14, 15, 17] The twin polymerization with the tin(II) alkox- ide D in the melt results in homogeneously distributed do- mains within the hybrid material 4 in contrast to 5, which was obtained from E. In addition twin polymerization of D was also performed in toluene solution to give 4s. Treatment of the hybrid materials 1-4 and 4s in an Ar/H2 (95/5 %) atmosphere at 600 8C gave 1-red-4-red and 4 s-red (Scheme 2). The Brunauer-Emmett-Teller (BET) surface areas of the reduced hybrid materials 1-red and 2-red amount to 161 and 263 m2 g^1, respectively, whereas the BET surface area of 3-red is quite low and amounts to 39 m2 g^1.

The formation of metallic tin nanoparticles was confirmed by electron diffraction (ED) studies and X-ray powder diffraction (XRPD) analyses. Average crystal- lite sizes of 38 (1-red), 28 (2- red), and 40 nm (3-red) were calculated using the Scherrer equation (Table 1; Figure S4). The XRPD analyses are in accordance with the TEM images, which ad- ditionally provide information on the distribution of the nanoparti- cles within the matrix. In 1-red the distribution of tin nanoparti- cles (size 15-52 nm) is homoge- neous over large areas (Figure 2).

Equally sized and homogene- ously distributed tin nanoparti- cles (13-30 nm) were deter- mined for 2-red (Figure 2). Com- pound 3-red shows a quite ho- mogeneous tin distribution, however, with large areas of densely and less densely packed tin particles with sizes around 14-54 nm. In addition a few par- ticles with sizes above 100 nm are observed. In the case of the hybrid material 4-red, which was prepared from the novel tin(II) alkoxide D, homogeneously distributed tin nanoparticles with crystallite sizes from 10 to 70 nm as determined by TEM and some residual SnO2 as determined by ED and XRPD are observed (Figure 3 ; Figure S5). The SnO2 most likely results from the disproportionation[23] of tin(II) oxide at temperatures above 350 8C to give tin and tin(IV) oxide and is not completely reduced under the conditions used.

In addition a small number of tin nanoparticles are located at the interface of the hybrid material (4-red), which is indica- tive of partial phase separation (Figure 3). In contrast to materi- als obtained in a melt-based process (4-red), a larger number of tin particles are located outside the C/SiO2 matrix for 4s- red, which is obtained from a solution-based process. Forma- tion of large tin particles outside the C/SiO2 matrix is not unex- pected given 1) the temperature of 600 8C used for the reduc- tion process (m.p. of tin 232 8C) and 2) the porous nature of the material. For example, the solution-based route for hybrid material 4 s-red gave a surface area of 352 m2 g^1 after reduc- tion. Compared to this the material produced by the melt- based process gave a BET surface area of 78 m2 g^1 (4-red). Consequently, this leads to a greater amount of leaching of tin nanoparticles to the surface for 4 s-red than for 4-red. Howev- er, the leaching process occurs predominantly for nanoparticles that are located close to the surface. For the hybrid material 4- red, the TEM images reveal that leaching of tin particles from the polymer matrix can almost be neglected (Figure 3). In addi- tion, the tin nanoparticles entrapped more deeply in the matrix do not sinter. It can be concluded that the polymeri- zation in melt as compared with the polymerization in solution results in hybrid materials with a more densely packed poly- mer/SiO2 matrix, and thus the tin nanoparticles are fixed in the following reduction process and therefore leaching is prevent- ed.

Hybrid materials prepared by addition of tin additives To investigate whether it is necessary to use polymerizable tin precursors such as A-E to produce homogeneously distributed tin nanoparticles by the twin polymerization process, the reac- tion of Si-spiro with Sn(OtBu)4, Sn(OnBu)2, Sn(OAc)4, and Sn(OAc)2 under various conditions was performed. The poly- merization of Si-spiro is initiated by the Lewis acidic nature of the tin additive (Figure 4).

At first several Si/Sn ratios (2:1, 6 ; 1:1, 7; 1:2, 8) were used for mixtures of Sn(OtBu)4 and Si-spiro. The polymerization reac- tions were performed in melt at 100 8C for half an hour and compact yellow solids were observed. For comparison, the pre- cipitation polymerization method in toluene was used for Sn- (OtBu)4 with a Si/Sn ratio of 2:1 to give 6s(Scheme 3).

Solid-state 13C NMR spectra of the hybrid materials 6-8 show signals that are assigned to the phenolic resin with ortho/ ortho' and ortho/para' substitution (Figure S6).[21] All samples that were polymerized in melt show, in contrast to 6s (precipi- tation polymerization method), a signal with a small width at half height at d =30 ppm, which is indicative of tert-butyl groups from embedded tin species Sn(OR)4^x(OtBu)x·ntBuOH (R =H, OAr) or residual tBuOH in the polymer. A small quantity of incompletely reacted silicon precursors and/or incompletely condensed silica is indicated by broad signals at about d = 68 ppm in the 13C NMR spectra and in the solid-state 29Si NMR spectra by signals at d=^95 to ^84ppm for thehybrid mate- rials 6-8 (Figure 5). Notably, the increase of the tin content leads to a shift in the 29Si NMR spectra of the hybrid materials from ^94 ppm (6)to^84 ppm (8), which indicates a decrease of the degree of cross-linking in the silica network.

The solid-state 119Sn NMR spectra show broad signals at d = ^638 (8), ^659 (6s), ^658 (6), and ^650 ppm (7), which points to an incorporation of hexacoordinated tin species Sn(OR)4^x(OtBu)x·ntBuOH (R= H, OAr) in the polymer matrix (Figure 6).[24-26] This assumption is reinforced by comparison of the solid-state 119Sn NMR data of the tetracoordinated tin atom in Sn(OtBu)4 (d=^371 ppm) with the hexacoordinated tin-648 ppm).[24] HAADF-STEM analyses of the hybrid materials 6-8 show the typical morphology of twin poly- mers with 2 nm sized domains (Figure 7).[14-16] In addition to Sn- (OtBu)4 the tin additives Sn- (OnBu)2 and the tin carboxylates Sn(OAc)2 and Sn(OAc)4 were tested for their potential in the synthesis of Sn/C/SiO2 materials (Scheme 3). They were mixed with Si-spiro in a Si/Sn ratio of 2 :1 and polymerized in 2,6-diiso-propylnaphthalene (for 9) or toluene (for 10 and 11) at 130 and 105 8C, respectively, for three hours (Scheme 3). The solid- state 13C NMR spectra of the hybrid materials 10 and 11 show signals for the phenolic resin with ortho/ortho' and ortho/para' substitution and some residual acetic acid (d = 24 and 175 ppm, Figure S8). The solid-state 29Si NMR spectra show sig- nals at ^97 (11) and ^98 ppm (10), which are in the same range as those observed for the hybrid materials 6-8 and is in- dicative of incompletely condensed silica (Figure S9). After the reduction process in an Ar/H2 atmosphere at 600 8C, the as-pre- pared materials 6-8 gave black Sn/C/SiO2 hybrid materials with BET surface areas of 103 m2g^1 for 6-red,92m2 g^1 for 7-red, and 67 m2 g^1 for 8-red (Table 1). The full conversion into em- bedded tin nanoparticles is indicated by XRPD and ED meas- urements (Figure S7). The final tin contents for selected Sn/C/ SiO2 materials were determined by X-ray fluorescence analyses to be in the range of 29 and 40 wt % (Table 1). The amount of tin was shown to depend on the number and nature of organ- ic ligands of the tin precursors as well as on the Sn/Si ratio used. In the reduced hybrid material 6-red (tin content : 32 wt %; Si/Sn= 2:1) the tin nanoparticles are uniformly distributed and they are about 35- 80 nm in size as determined by TEM.

The average crystallite size as calculated by the Scherrer equa- tion amounts to 53 nm. A similar and quite homogeneous distri- bution of tin nanoparticles is ob- served for 6 s-red, which was ob- tained by the precipitation poly- merization method (Figure 7). The average crystallite size is 50 nm (based on XRPD). Howev- er, the obtained polymer matrix is not as dense as in 6-red and tin particles outside of the C/SiO2 matrix as result of leach- ing are obtained. This observa- tion correlates to the higher sur- face area of 6 s-red (206 m2 g^1) relative to 6-red (103 m2g^1). For compound 7-red a similar aver- age tin crystallite size of 61 nm is determined based on XRPD, but TEM images reveal an in- creased variation in particle size (20-120 nm), which might be as- signed to the higher tin content of 37 wt % (Figure 7). Further in- crease of the tin content to 40 wt% in 8-red results in tin particles that build agglomerates up to 200 nm in size even within the C/SiO2 matrix. In conclusion, the polymerization in melt using Sn(OtBu)4 as additive provides for all samples (6-red-8-red) a dense polymer matrix with em- bedded tin particles even for a tin content of 40 wt %. For comparison, Sn(OnBu)2, Sn(OAc)2, and Sn(OAc)4 were used in the additive-based twin polymerization to give the hybrid ma- terials 9-11 by precipitation polymerization in toluene (Scheme 3). TEM images show the typical morphology of twin polymers and tin contents between 31 and 33 wt %. Analysis of the HAADF-STEM images reveals a tin nanoparticle size within the C/SiO2 matrix of 12-30 (9-red), 10-20 (10-red), and 10-50 nm (11-red) (Figure 8), in all cases accompanied by some larger particles. The crystallite sizes calculated by the Scherrer equation amount to 49 (9-red), 35 (10-red), and 43 nm (11-red) (Table 1; Figure S10). As result of their porous polymer matrices and high BET surface areas of 332 (9-red), 316 (10-red), and 274 m2 g^1 (11-red), large tin particles with sizes above 100 nm and increased leaching are observed for all samples (Figure 8, Table 1). In contrast to the results obtained for Sn(OtBu)4 as additive in the twin polymerization process, homogeneously distributed tin nanoparticles were not ob- tained upon use of Sn(OnBu)2, Sn(OAc)2, and Sn(OAc)4.

Conclusion The concept of twin polymerization was used for the synthesis of Sn/C/SiO2 hybrid materials by two different approaches. The first approach was based on the simultaneous twin polymeri- zation of 2,2'-spirobi[4H-1,3,2-benzodioxasiline] (Si-spiro) with tin(IV) alkoxides (A-C) and tin(II) alkoxides (D and E), which contain polymerizable organic ligands. First, hybrid materials composed of tin oxo species, silica, and a phenolic resin were observed, which after treatment under reducing conditions (Ar/H2, at 600 8C) gave Sn/C/SiO2 hybrid materials with tin nanoparticles (28-48 nm) and homogeneous distribution of the latter within the C/SiO2 matrix. In the second approach the twin polymerization of Si-spiro was performed in the presence of different tin additives, such as Sn(OtBu)4, Sn(OnBu)2, Sn(OAc)2, and Sn(OAc)4 (additive-based twin polymerization). The polymerization was initiated by the Lewis acidic nature of the tin compounds and led successfully to hybrid materials, which were converted under reducing conditions into Sn/C/ SiO2 hybrid materials with tin nanoparticles embedded in the C/SiO2 matrix. However, only Sn(OtBu)4 gave a homogeneous distribution of tin nanoparticles in the matrix, similar to materi- als prepared by simultaneous twin polymerization. Both ap- proaches offer the possibility to control the resulting particle size (10-200 nm) of the embedded tin particles by the use of different tin contents in the starting materials, and both pro- cesses can be performed either in the melt or in solution (pre- cipitation twin polymerization method). However, the polymer- ization in melt is favored because it results in dense polymer matrices after twin polymerization, and thus leaching of tin nanoparticles and sintering during the reduction process is prevented. Materials observed by the precipitation method show high surface areas and thus increased leaching. The use of Sn(OnBu)2, Sn(OAc)2, and Sn(OAc)4 as tin additives gave hybrid materials that showed the highest degree of leaching and a large particle size distribution, which are attributed to the porous nature of the materials with BET surface areas up to 352 m2 g^1. Thus, Sn(OtBu)4 is favored in the additive-based twin polymerization.

Experimental Section All reactions were performed under an inert argon atmosphere using the Schlenk technique. Chloroform was distilled over CaH2 before use. Diethyl ether, n-hexane, n-butanol, and toluene were dried over sodium and freshly distilled prior to use. 2-(Hydroxy- methyl)-4-methoxyphenol and 2-(hydroxymethyl)-5-methoxyphenol were prepared from 4-methoxyphenol and 5-methoxyphenol, re- spectively, using a published procedure.[27] Tin(IV) tert-butoxide,[24] tin(II) n-butoxide,[28] tin(II) acetate,[29] tin(IV) acetate,[30] tin(II) meth- oxide,[28] 2,2'-spirobi[4H-1,3,2-benzodioxasiline] ,[15, 17] 2,2'-spirobi[4H- 1,3,2-benzodioxastannine] (A),[13] 2,2'-spirobi[6-methyl-4H-1,3,2-ben- zodioxastannine] (B),[13] and 2,2'-spirobi[6-methoxy-4H-1,3,2-benzo- dioxastannine] (C)[13] were prepared according to literature proce- dures. Solid-state NMR measurements were performed at 9.4 T on a Bruker Avance 400 spectrometer equipped with double-tuned probes capable of magic angle spinning. 13C{1H} cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy was accom- plished in 4 mm rotors made of zirconium oxide spinning at 12.5 kHz. Cross-polarization with contact time of 3 ms was used to enhance sensitivity. The recycle delay was 5 s. 29Si {1H} CP-MAS NMR spectroscopy was performed in 7 mm rotors spinning at 5 kHz. The contact time was 3 ms and the recycle delay 5 s. 119Sn {1H} MAS NMR spectroscopy was performed in 4 mm rotors spinning at 12.5 kHz. The recycle delay was 10 s. All spectra were obtained under 1H decoupling using a two-pulse phase modulation se- quence. The spectra were referenced with respect to tetramethylsi- lane using tetrakis(trimethylsilyl)silane and tetracyclohexylstannane as standards (3.6 ppm for 13C, ^9.5 ppm for 29Si, ^97.3 ppm for 119Sn). If not stated otherwise, all spectra were acquired at room temperature. X-ray powder diffraction (XRPD) analysis was per- formed with a STOE-STADI-P powder diffractometer with CuKa1 ra- diation in the range 5-708 for 2q. Brunauer-Emmett-Teller (BET) surface area measurements were performed with a Micromeritics gadget type Gemini S. Differential scanning calorimetry (DSC) ex- periments were determined by using a Mettler Toledo DSC 30 in- strument with a 40 mL aluminum crucible. The measurements were performed up to 350 8C with a heating rate of 10 K min^1 in N2 at- mosphere and a volume flow of 50 mL min^1. For X-ray fluores- cence analysis a MiniPal PW 4025/00 X-ray spectrometer with a rho- dium anode (type TFS 5109/Rh) at 15 kV and 0.040 mA was used (regression factor = 1.6 %). HAADF-STEM analysis was performed by using an FEI Tecnai F20 field-emission TEM instrument. The sam- ples (embedded in an epoxy resin) were ultrathin, cut by a Leica UCT ultramicrotome. The ultrathin slices were transferred onto a carbon-coated perforated copper grid.

Synthesis of tin monomers Synthesis of tin(II)-5-methoxy-2-(oxidomethyl)-phenolate (E): 2-Hy- droxy-4-methoxybenzyl alcohol (1.77 g, 11.5 mmol) in toluene (5 mL) was added dropwise to a suspension of tin(II) methoxide (2.08 g, 11.5 mmol) in toluene (50 mL). After stirring for 1 h at room temperature the resulting methanol was removed in vacuo and the suspension changed to a clear solution. The remaining solvent was evaporated and the residue was washed several times with di- ethyl ether and dried under vacuum (10^3 mbar). Yield 2.78 g (10.2 mmol, 89 %) of a pale yellow solid.

Decomposed at 2508C; 1H NMR (500.3 MHz, CDCl3): d = 6.96 (br, 3H; aryl groups), 4.7(br,2H; CH2),3.64ppm (br, 3H; OCH3);13C{1H} CP-MAS NMR (100.6 MHz): d =54.9, 66.0, 103.2, 108.0, 117.8, 130.7, 157.0 159.6 ppm; 119Sn {1H} MAS NMR (149.2 MHz): d = ^422 ppm; IR: ñ=2933 (w), 2904 (w), 2830 (w), 1601 (m), 1570 (m), 1487 (s), 1433 (s), 1275 (s), 1194 (s), 1154 (s), 1101 (s), 1032(s), 955 (s), 829 (m), 789 (m), 733 (m), 502 (s), 443 cm^1 (s) ; elemental analysis calcd (%) for C8H8O3Sn (270.86): C 35.47, H 2.98 ; found : C 34.7, H 3.2.

Synthesis of tin(II)-4-methoxy-2-(oxidomethyl)-phenolate (D): The compound was prepared according to the procedure for tin(II)-5- methoxy-2-(oxidomethyl)-phenolate using Sn(OMe)2 (1.23 g, 6.8 mmol), 2-hydroxy-5-methoxybenzyl alcohol (1.05 g, 6.8 mmol), and toluene (50 mL). Yield 1.50 g (5.5 mmol, 81 %) of a pale yellow solid.

Decomposed at 2608C; 1H NMR (500.3 MHz, CDCl3): d = 6.66 (br, 3H; aryl groups), 4.7(br,2H; CH2),3.66ppm (br, 3H; OCH3);13C{1H} CP-MAS NMR (100.6 MHz): d =55.1, 65.7, 111.2, 116.2, 127.9, 149.2, 153.5ppm; 119Sn{1H}MAS NMR(149.2MHz):d=^420ppm;IR: ñ= 2939 (w), 2901 (w), 2830 (w), 1603 (w), 1576 (w), 1479 (s), 1423 (m), 1263 (m), 1198 (s), 1150 (s), 1115 (w), 1032(s), 928 (w), 855 (m), 791 (s), 635 (m), 507 (s), 434 cm^1 (s) ; elemental analysis calcd (%) for C8H8O3Sn (270.86): C 35.47, H 2.98 ; found : C 35.0, H 3.1.

Synthesis of hybrid materials Hybrid materials 1-3 were prepared from 2,2'-spirobi[4H-1,3,2-ben- zodioxastannine] (A ; 0.70 g, 1.9 mmol), 2,2'-spirobi[6-methyl-4H- 1,3,2-benzodioxastannine] (B ; 0.60 g, 1.5 mmol), and 2,2'-spirobi[6- methoxy-4H-1,3,2-benzodioxastannine] (C ; 0.60 g, 1.4 mmol) in combination with 2,2'-spirobi[4H-1,3,2-benzodioxastannine] by using a published procedure.[13] Hybrid material 4 : 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.80 g, 6.6 mmol) and tin(II)-2-(oxidomethyl)-4-methoxyphenolate (D ; 0.60 g, 2.2 mmol) were dissolved in chloroform (20 mL). The sol- vent was removed after stirring for a few minutes and the mixture was heated slowly to 90 8C for half an hour. The yellow solid was washed with acetone (15 mL) and dried at 70 8C.

Hybrid material 4s: A precipitation polymerization method in tolu- ene was used. 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (3.0 g, 11.0 mmol) and tin(II)-2-(oxidomethyl)-4-methoxyphenolate (D ; 1.0 g, 3.7 mmol) were suspended in toluene (20 mL) and heated to 100 8C for 3 h. At 808C the suspension changed to a clear solution and at 95 8C a precipitate was formed. After stirring for 3 h at 100 8C the colorless solid was isolated by filtration, washed with acetone (15 mL), and dried at 70 8C.

Hybrid material 5 : 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.80 g, 6.6 mmol) and tin(II)-2-(oxidomethyl)-5-methoxyphenolate (E ; 0.60 g, 2.2 mmol) were dissolved in chloroform (20 mL). The sol- vent was removed after stirring for a few minutes and the mixture was heated slowly to 90 8C for half an hour. The light red solid was washed with acetone (15 mL) and dried at 70 8C.

Hybrid materials 6-8 : 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.0 g, 3.7 mmol) and Sn(OtBu)4 were mixed with Si/Sn ratios of 2 :1 (for 6) and 1:1 (for 7) and subsequently heated to 100 8C for 30 min. The reaction mixture with a Si/Sn ratio of 1:2 (for 8) was heated to 120 8C under vacuum (to remove tBuOH) for 1 h. The yellow solid was washed with acetone (15 mL) and dried at 70 8C.

Hybrid material 6s: 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.0 g, 3.7 mmol) and Sn(OtBu)4 (0.75 g, 1.84 mmol) were dissolved in tol- uene (15 mL) and heated to 90 8C for 3 h. After stirring for 3 h at 100 8C the slightly yellow solid was isolated by filtration, washed with acetone (15 mL), and dried at 70 8C.

Hybrid material 9 : 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.40 g, 5.1 mmol) and Sn(OnBu)2 (0.70 g, 2.6 mmol) were suspended in 2,6-diisopropylnaphthalene (12 mL). Heating to 100 8C changed the suspension to a yellow solution and at 130 8C a yellow precipitate was observed. After further stirring for 3 h at 130 8C the solid was isolated by filtration, washed with acetone (15 mL), and dried at 708C.

Hybrid materials 10 and 11: 2,2'-Spirobi[4H-1,3,2-benzodioxasiline] (1.40 g, 5.1 mmol) and Sn(OAc)2 (0.60 g, 2.5 mmol ; or 10)or Sn(OAc)4 (0.90 g, 2.5 mmol ; for 11) were dissolved in toluene (20 mL). The reaction mixture was then heated to 105 8C for 3 h. A colorless solid was isolated by filtration, washed with acetone (15 mL), and dried at 70 8C.

Reduction process All reduction processes of the hybrid materials were performed in a tube furnace with a heating rate of 5 K min ^ 1, a final reaction temperature of 600 8C, and a reaction time of 4 h in total for mate- rials 1-red-3-red and 2 h for materials 4-red-11-red. The solids were treated constantly with an Ar/H2 (95/5 %) stream of flow rate 30 L h^1 to give black solids composed of Sn/C/SiO2 in all cases.

Acknowledgements We are grateful to BASF SE (Ludwigshafen, Germany) and the Deutsche Forschungsgemeinschaft (FOR 1497) for financial sup- port, Janine Fritzsch and Ute Stçß for performing C,H analyses, and Prof. S. Spange for access to differential scanning calorimetry and X-ray fluorescence spectroscopy. We are very grateful to the late Dr. Gerhard Cox (BASF SE) for supporting this work with ex- cellent TEM analysis and dedicate this article to him.

[1] S. Huang, Y. Chen, H. Xiao, F. Lu, Surf. Coat. Technol. 2010, 205, 2247.

[2] Y. Lei, P. Moeck, T. Topuria, N. D. Browning, R. Ragan, K. S. Min, H. A. At- water, Appl. Phys. Lett. 2003, 82, 4262.

[3] A. Nakajima, T. Futatsugi, H. Nakao, T. Usuki, N. Horiguchi, N. Yokoyama, J. Appl. Phys. 1998, 84, 1316.

[4] S. Huang, E.-C. Cho, G. Conibeer, M. A. Green, Thin Solid Films 2011, 520, 641.

[5] X. L. Zhao, K. F. Wang, W. F. Zhang, M. J. Huang, Y. L. Mao, Appl. Surf. Sci. 2010, 256, 6427.

[6] S. Huang, E. C. Cho, G. Conibeer, M. A. Green, D. Bellet, E. Bellet-Amalric, S. Y. Cheng, J. Appl. Phys. 2007, 102, 114304.

[7] J. M. J. Lopes, F. Kremer, P. F. P. Fichtner, F. C. Zawislak, Nucl. Instrum. Methods Phys. Res. Sect. B 2006, 242, 157.

[8] H. Huang, E. M. Kelder, L. Chen, J. Schoonman, J. Power Sources 1999, 81, 362.

[9] B. Liu, A. Abouimrane, D. E. Brown, X. Zhang, Y. Ren, Z. Z. Fang, K. Amine, J. Mater. Chem. A 2013 , 1, 4376.

[10] J. Hwang, S. H. Woo, J. Shim, C. Jo, K. T. Lee, J. Lee, ACS Nano 2013, 7, 1036.

[11] M. Hoch, Appl. Geochem. 2001, 16, 719.

[12] P. V. Silva, A. R. R. Silva, S. Mendo, S. Loureiro, Sci. Total Environ. 2014, 466 - 467, 1037.

[13] C. Leonhardt, S. Brumm, A. Seifert, G. Cox, A. Lange, T. R^ffer, D. Schaarschmidt, H. Lang, N. Jçhrmann, M. Hietschold, F. Simon, M. Mehr- ing, ChemPlusChem 2013, 78, 1400.

[14] S. Grund, P. Kempe, G. Baumann, A. Seifert, S. Spange, Angew. Chem. 2007, 119, 636 ; Angew. Chem. Int. Ed. 2007, 46, 628.

[15] S. Spange, P. Kempe, A. Seifert, A. A. Auer, P. Ecorchard, H. Lang, M. Falke, M. Hietschold, A. Pohlers, W. Hoyer, G. Cox, E. Kockrick, S. Kaskel, Angew. Chem. 2009, 121, 8403 ; Angew. Chem. Int. Ed. 2009, 48, 8254.

[16] S. Spange, S. Grund, Adv. Mater. 2009, 21,2111.

[17] F. Bçttger-Hiller, R. Lungwitz, A. Seifert, M. Hietschold, M. Schlesinger, M. Mehring, S. Spange, Angew. Chem. 2009, 121, 9039 ; Angew. Chem. Int. Ed. 2009, 48, 8878.

[18] A. A. Auer, A. Richter, A. V. Berezkin, D. V. Guseva, S. Spange, Macromol. Theory Simul. 2012, 21, 615.

[19] T. Lçschner, A. Mehner, S. Grund, A. Seifert, A. Pohlers, A. Lange, G. Cox, H.-J. H^hnle, S. Spange, Angew. Chem. 2012, 124, 3312 ; Angew. Chem. Int. Ed. 2012, 51, 3258.

[20] P. Kitschke, A. A. Auer, A. Seifert, T. R^ffer, H. Lang, M. Mehring, Inorg. Chim. Acta 2014, 409 (B), 472.

[21] R. L. Bryson, G. R. Hatfield, T. A. Early, A. R. Palmer, G. E. Maciel, Macro- molecules 1983, 16, 1669.

[22] P. Kitschke, A. A. Auer, T. Lçschner, A. Seifert, S. Spange, T. R^ffer, H. Lang, M. Mehring, ChemPlusChem 2014, 79, DOI : 10.1002/ cplu.201402029.

[23] D. Aurbach, A. Nimberger, B. Markovsky, E. Levi, E. Sominski, A. Gedank- en, Chem. Mater. 2002, 14, 4155.

[24] M. J. Hampden-Smith, T. A. Wark, Can. J. Chem. 1991, 69, 121.

[25] J. Caruso, M. J. Hampden-Smith, A. L. Rheingold, G. Yap, J. Chem. Soc. Chem. Commun. 1995, 157.

[26] N. Kishor Mal, V. Ramaswamy, S. Ganapathy, A. V. Ramaswamy, Appl. Catal. A: Gen. 1995, 125, 233.

[27] Ø. W. Akselsen, L. Skattebøl, T. V. Hansen, Tetrahedron Lett. 2009, 50, 6339.

[28] R. Gsell, M. Zeldin, J. Inorg. Nucl. Chem. 1975, 37, 1133.

[29] J. D. Donaldson, W. Moser, W. B. Simpson, J. Chem. Soc. 1964, 5942.

[30] A. K. Sawyer, C. Frey, R. A. Collupy, R. I. Chase, Syn. React. Inorg. Met. 1989, 19, 969.

Received : May 6, 2014 Published online on July 10, 2014 Christian Leonhardt,[a] Susann Brumm,[a] Andreas Seifert,[b] Arno Lange,[c] Szilard Csihony,[c] and Michael Mehring*[a] [a] C. Leonhardt, S. Brumm, Prof. Dr. M. Mehring Institut f^r Chemie, Professur Koordinationschemie Fakult^t f^r Naturwissenschaften, Technische Universit^t Chemnitz Strasse der Nationen 62, 09107 Chemnitz (Germany) Fax: (+ 49) (0)-371-531-21219 E-mail : [email protected] [b] Dr. A. Seifert Institut f^r Chemie, Professur Polymerchemie Fakult^t f^r Naturwissenschaften, Technische Universit^t Chemnitz Strasse der Nationen 62, 09107 Chemnitz (Germany) [c] Dr. A. Lange, Dr. S. Csihony BASF SE Carl-Bosch Strasse 38, 67056 Ludwigshafen (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201402137.

(c) 2014 Blackwell Publishing Ltd.

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