J O U R N A L O F C H E M I S T R Y Materials Preparation method for organic–inorganic layered compounds including fibrous materials by the reaction of Zn(OH)2 with organic compounds Sumikazu Ogata,a Izumi Miyazaki,a Yoshiharu Tasaka,b Hideyuki Tagaya,*a Jun-ichi Kadokawaa and Koji Chibaa aDepartment of Materials Science and Engineering, Yamagata University, Yonezawa, Yamagata 992, Japan. E-mail: tc021@dip.yz.yamagata-u.ac.jp bNational Institute of Materials and Chemical Research, Higashi, Tsukuba, Ibaraki 305, Japan Received 16th June 1998, Accepted 17th September 1998 A preparation method of surface modified inorganic layered compounds including fibrous materials was established by the reaction of amorphous Zn(OH)2 with organic oxychlorides.The resultant layer structures were similar to those of the layered double hydroxides (LDHs).Although the LDH layers have positive charges the layers of the reaction products obtained here are uncharged. IR spectra indicate that hydroxyl groups reacted with the organic oxychlorides, and new peaks assigned to RCO2–Zn bonds appeared around 1400 and 1550 cm-1 and 40–98% of hydroxyl groups were reacted.Interlayer spacings of the reaction products of Zn(OH)2 with dioxychlorides were 0.71–1.48 nm, and those of Zn(OH)2 with monooxychlorides were 1.19–2.67 nm and depended on the length of organic compounds. SEM images showed that the reaction products of Zn(OH)2 with organic oxychlorides had plate-like morphology similar to LDHs. However, the reaction product of Zn(OH)2 with benzoyl chloride was fibrous. Recently, the preparation of various organic–inorganic hybrid reacted with Zn(OH)2 giving surface modified layered compounds.The products diVer from the surface modified Zn/Al materials has been reported.1 Incorporation of a molecule into LDHs since their layers are uncharged and inclusion of anionic a crystalline inorganic host lattice to form an intercalation compounds between the layers is not required.compound can lead to ordered materials.2,3 For example, it In this study, we have prepared and characterized layered has been extensively reported that metal phosphonates are organic–inorganic compounds including fibrous materials useful for organizing molecules into lamellar structures.4 by the reaction of amorphous Zn(OH)2 with organic Their structures are very similar to those formed by oxychlorides.Langmuir–Blodgett (LB) techniques, but have higher thermal stabilities than LB films.5 Recently, attempts on the preparation of new organic derivative nanocomposites have been Experimental reported.6,7 It is possible to bond organic molecules on the surface of metal phosphonate covalently by the reaction of Reagents phosphate hydroxyl groups with organic compounds.Thus, All reactions were carried out using commercial reagents. the reaction of hydroxyl groups with organic compounds leads n-Butyryl chloride [CH3(CH2)2COCl], hexanoyl chloride to organic derivatived hybrid materials. These chemical modi- [CH3(CH2)4COCl], glutaryl dichloride [ClCO(CH2)3COCl] fications included reactions of inorganic compounds with and adipoyl chloride [ClCO(CH2)4COCl] were purchased alcohols.from Tokyo Chemical Industry Co. Zn(OH)2, suberoyl We have already reported the preparation method for chloride [ClCO(CH2)6COCl], sebacoyl chloride [ClCO- inorganic layered compounds the surfaces of which are modi- (CH2)8COCl ] and dodecanedioyl dichloride [ClCO(CH12)10COCl ] fied by organic compounds.In this reaction, a water-treated were purchased from Aldrich Chemical Co. Phenylacetyl Zn/Al layered double hydroxide (LDH) was prepared by chloride [C6H5CH2COCl], benzoyl chloride (C6H5COCl), placing the calcined Zn/Al LDH in degassed water and reacting Mg(OH)2, Cu(OH)2 and Ni(OH)2 were purchased from with an organic oxychloride in organic solvent. The resultant Wako Chemical Co.Al(OH)3 was purchased from Kanto compound is a well organized organic–inorganic hybrid mate- Chemical Co. rial, and the interlayer space is hydrophobic. The LDH is an inorganic layered compound8 and many organic intercalates Surface modification reactions of metal hydroxides into LDHs are known.9–13 Since the LDH layer has a positive charge, the LDH undergoes anion exchange intercalation Zn(OH)2 (0.2 g; 2.01 mmol) and other metal hydroxides such reactions with guests such as organic acids and inorganic as Cu(OH)2, Ca(OH)2 , Ni(OH)2 , Mg(OH)2 and Al(OH)3 anions.The surface modified LDH also has a positive charge were reacted with 0.4 equivalents of organic oxychlorides in 3 and includes anionic compounds between the layers.14,15 or 5 ml of acetonitrile or diethyl ether for 5 h under stirring On the other hand, chemical surface modification of at 333 K.For benzoyl chloride the reaction product of Zn(OH)2 was reported in which Zn(OH)2 was reacted with Zn(OH)2 with 0.4 equivalents of benzoyl chloride dissolved methanol at 588 K. In this reaction hydroxy ions were substi- in the solvent. Therefore, the reaction was repeated using 0.2 tuted by methoxy ions.16 Recently, we have described a method equivalents of benzoyl chloride.After being filtered oV, the to prepare new surface modified inorganic layered compounds reaction products were washed with the same solvent to by the reaction of Zn(OH)2 with organic oxychlorides at remove unreacted organic oxychlorides and impurities, and dried under reduced pressure at room temperature. 333 K.17 Not only monooxychlorides but also dioxychlorides J. Mater. Chem., 1998, 8, 2813–2817 2813Characterization Powder X-ray diVraction (XRD) spectra were recorded on a Rigaku powder diVractometer unit, using Cu-Ka (filtered) radiation (l=0.154 nm) at 40 kV and 20 mA between 1.8 and 50°. FTIR spectra (KBr disc method) were recorded on a Horiba FT-200 apparatus. Thermogravimetric analysis (TG) and diVerential thermal analysis (DTA) of powdered samples up to 873 K were carried out at a heating rate of 10 K min-1 under flowing N2 using a Seiko SSC5000 thermal analysis system.Scanning electron microscopy (SEM) was performed with a JEOL JSM-5300 instrument, operating at 20 kV. Results and discussion Thermal characteristics of the reaction products of Zn(OH)2 with organic oxychlorides Thermal characteristics of the reaction products of Zn(OH)2 with organic oxychlorides were determined by TG analysis. For Zn(OH)2, weight loss was observed up to 343 K as shown in Fig. 1(a) and corresponded to dehydration of Zn(OH)2. For benzoyl chloride weight loss was observed up to 470 K as shown in Fig. 1(c). For the reaction product of Zn(OH)2 with Fig. 2 XRD patterns of the reaction products of Zn(OH)2 with benzoyl chloride, two weight loss regions were observed (a) hexanoyl chloride, (b) suberoyl chloride, (c) benzoyl chloride, and between 450 and 720 K as shown in Fig. 1(b). The first weight (d) Zn(OH)2 alone. loss near 450 K corresponded to the dehydration of OH groups of Zn(OH)2 and desorption of organic groups reacted on the outer surface of Zn(OH)2.The second weight loss at between similar crystalline products were obtained by the reaction with 570 and 720 K corresponded to desorption of organic groups suberoyl chloride or benzoyl chloride in acetonitrile or diethyl reacted on the inner surface of Zn(OH)2. Certainly, the ether. Interlayer spacings of these reaction products were 1.67, reaction product of Zn(OH)2 with benzoyl chloride was more 1.08 and 1.48 nm as shown in Fig. 2(a), (b) and (c), respectstable thermally than benzoyl chloride itself. Similar thermal ively. The XRD peaks of these reaction products were diVerent stabilities were observed for other reaction products of from those of the individual organic oxychlorides and car- Zn(OH)2 with organic oxychlorides.boxylic acids. We have already reported that water-treated Zn/Al LDHs reacted with various organic oxychlorides to give X-Ray powder diVraction patterns of the reaction products surface modified LDHs.14,15 These were diVerent from those of intercalation compounds of organic carboxylate anions.18,19 No clear peaks were observed in the XRD pattern of Zn(OH)2 Upon reaction of sebacic acid with calcined Zn/Al LDH in alone as shown in Fig. 2(d). Upon reaction of this amorphous water, an intercalation compound was obtained, and the Zn(OH)2 with 0.4 equivalents of hexanoyl chloride in acetointerlayer spacing increased to 1.88 nm (Table 1). This value nitrile, a crystalline product was obtained, although the reacis larger than the spacing of 1.28 nm for the surface modified tion product dissolved in acetonitrile in the reaction of LDH.XRD peak patterns of all reaction products except that Zn(OH)2 with 1.0 equivalents of hexanoyl chloride. Crystalline of Zn(OH)2 with benzoyl chloride were similar to those of Zn(OH)2 was prepared by the reaction of Zn(NO3)2 with the surface modified Zn/Al LDH in which the water-treated NaOH, and was reacted with organic oxychlorides. The reac- Zn/Al LDH was reacted with oxychlorides.In the reaction tivity of crystalline Zn(OH)2 with organic compounds is fairly products of Zn(OH)2 with straight chain oxychlorides such as low, and peaks of Zn(OH)2 remained even after reaction with hexanoyl chloride and suberoyl chloride, the interlayer spac- organic oxychlorides. In the reaction of amorphous Zn(OH)2, ings of the reaction products increased with an increase in Table 1 XRD profiles of the reaction products of Zn(OH)2 with organic oxychlorides d-value/nm Oxychloride Length/nm OH-LDHa LDHb Zn(OH)2 n-Butyryl chloride 0.47 1.18 1.19 Hexanoyl chloride 0.72 1.61 1.67 Benzoyl chloride 0.54 1.12 1.54 1.48 Phenylacetyl chloride 0.61 1.54 1.53 p-Phenylazobenzoyl 1.16 2.67 2.28 2.67 chloride Glutaryl dichloride 0.51 0.71 Adipoyl chloride 0.64 0.77 1.48 0.83 Suberoyl chloride 0.89 1.07 1.08 Sebacoyl chloride 1.14 1.28 1.88 1.28 Dodecanedioyl 1.40 1.52 2.28 1.48 dichloride aThe reaction products of the water-treated LDHs with various organic oxychlorides.14 bThe intercalation compounds of correspond- Fig. 1 Thermal analysis of (a) Zn(OH)2, (b) the reaction product of ing organic anions into the Zn/Al LDHs.Zn(OH)2 with benzoyl chloride and (c) benzoyl chloride. 2814 J. Mater. Chem., 1998, 8, 2813–2817products, no absorption peaks corresponded to carboxylic acids or dimers of the organic reactants. In the IR spectra of the reaction products of Zn(OH)2 with straight chain type oxychlorides such as hexanoyl chloride and suberoyl chloride, n(CKH) at ca. 2900 and 2800 cm-1 as well as d(CKH) at ca. 1470 cm-1 were observed. In the IR spectrum of the reaction product of Zn(OH)2 with benzoyl chloride a new peak at 1600 cm-1 was observed and assigned to n(CLC) of the benzene ring. n(OH) absorptions at ca. 3500 cm-1 in the IR spectrum of Zn(OH)2 decreased upon reaction with organic oxychlorides and new peaks at ca. 1540 and 1400 cm-1 appeared. The absorption peak at 1540 cm-1 is assigned to the asymmetric stretching vibration of carboxylate, and the absorption at 1400 cm-1 assigned to the symmetric stretching vibration of Fig. 3 Interlayer spacings of the intercalation compound of Zn/Al LDH (&), the reaction products of Zn(OH)2 with ClCO(CH2)nCOCl carboxylate. The presence of these two peaks suggest the (n=4, 6, 8 and 10) (%), and CH3(CH2)nCOCl (n=2 and 4) (#).formation of RCO2–Zn bonds by reaction of Zn(OH)2 with organic oxychlorides. These results indicate the formation of surface modified layered compounds as shown in Fig. 5. methylene chain length as shown in Fig. 3. However, the To clarify the mechanism of the formation of the layered interlayer spacings of the reaction product of Zn(OH)2 with compounds, Zn(OH)2 was reacted with an excess of oxychlor- monooxychlorides were larger than those of Zn(OH)2 with ide and the product was dissolved in an organic solvent such dioxychlorides. The interlayer spacing and the length of oxyas acetonitrile or diethyl ether.Upon evaporation of aceto- chlorides suggested that the reaction products from nitrile or ether, powders were obtained the IR spectrum of monooxychlorides were bilayer structures and the reaction which indicated the presence of RCO2–Zn bonds while XRD products from dioxychlorides were bridging structures. showed the formation of carboxylic acid.The interlayer spacing of the reaction product of Zn(OH)2 It is proposed that the first step of the reaction of Zn(OH)2 with phenylacetyl chloride was 1.53 nm.The value was similar with monooxychlorides (RCOCl) is a dehydration reaction to that (1.54 nm) of the reaction product of the water-treated between OH groups of Zn(OH)2 and RCOCl to give Zn/Al LDH with phenylacetyl chloride. However, in the RCO2–Zn–OH or RCO2–Zn–OCOR. The cross-sectional area reaction product of Zn(OH)2 with benzoyl chloride, the of one HO–Zn–OH unit22 is calculated to be 0.96 nm2.It is interlayer spacing was 1.48 nm and larger than that of the proposed that the layered structure is assembled by interacting reaction product of the water-treated LDH with benzoyl RCO2–Zn–OH or RCO2–Zn–OCOR units as shown in Fig. 5. chloride (1.12 nm). The d-spacing of zinc benzoate However, the cross-sectional area of RCO2–Zn–OCOR is [Zn(C6H5CO2)2]20 was 1.10 nm.21 The XRD pattern of the >0.96 nm2 and therefore, an excess amount of reaction product of Zn(OH)2 with benzoyl chloride was RCO2–Zn–OCOR might interfere with the assembly reaction diVerent to that of zinc benzoate.owing to steric repulsion. IR spectroscopy The IR spectra of Zn(OH)2 and its reaction products with organic oxychlorides are shown in Fig. 4. In all reaction Fig. 4 IR spectra of (a) Zn(OH)2, the reaction product of Zn(OH)2 Fig. 5 Reaction of Zn(OH)2 with organic oxychlorides to give with (b) benzoyl chloride, (c) suberoyl chloride, and (d) hexanoyl chloride. 2: RCO2–Zn band. organic–inorganic hybrid layered compounds. J. Mater. Chem., 1998, 8, 2813–2817 2815Table 2 Elemental analysis of the reaction products of Zn(OH)2 with organic oxychlorides, Zn(OH)x(OKG)y or Zn(OH)x(OKGKO)z Oxychloride C(%) H(%) x y z n-Butyryl chloride 32.94 4.80 0.31 1.69 — Hexanoyl chloride 42.80 6.49 0.58 1.42 — Benzoyl chloridea 41.26 2.83 1.00 1.00 — Phenylacetyl chloride 52.57 3.88 0.46 1.54 — p-Phenylazobenzoyl chloride 47.23 3.07 1.19 0.81 — Glutaryl dichloride 23.68 2.48 0.74 — 0.63 Adipoyl chloride 34.10 3.83 0.04 — 0.98 Suberoyl chloride 34.89 4.29 0.54 — 0.73 Sebacoyl chloride 40.50 5.41 0.50 — 0.75 Dodecanedioyl dichloride 43.82 6.04 0.52 — 0.74 aFibrous. Composition of organic–inorganic layered compounds Elemental analyses of the reaction products of Zn(OH)2 with organic oxychlorides are shown in Table 2.About 85% of the OH groups of Zn(OH)2 reacted with hexanoyl chloride to assemble a layered structure and for cases of straight chain oxychlorides and phenylacetyl chloride, 63–98% of OH groups reacted.However, for bulky oxychlorides, such as benzoyl chlorides and p-phenylazobenzoyl chloride (C6H5NNC6H4COCl), only ca. 50 and 40%, respectively, of OH groups react. The results indicate that the extent of reaction of OH groups in Zn(OH)2 depends on the structure Fig. 6 SEM images (5000 ×magnification) of (a) Zn(OH)2 and the reaction products of Zn(OH)2 with (b) hexanoyl chloride, (c) suberoyl of the oxychloride. chloride and (d) benzoyl chloride. Reaction of Cu(OH)2, Mg(OH)2, Ni(OH)2 and Al(OH)3 with oxychloride We have already reported that water-treated Zn/Al LDHs react with organic oxychlorides to give surface modified LDHs.14,15 However, we could not obtain a water-treated Mg/Al LDH, and Mg/Al LDH scarcely reacted with oxychlorides. Furthermore, Al(OH)3, Cu(OH)2 and Ni(OH)2 did not react with oxychlorides. We confirmed reaction of Mg(OH)2 with oxychlorides, however, the amounts of reacted OH groups were small, and XRD peaks of the products were not clear. Morphology of the reaction product of Zn(OH)2 with organic compounds Zn(OH)2 has a plate-like morphology as shown in Fig. 6(a). Upon reaction of Zn(OH)2 with hexanoyl chloride and suberoyl chloride, clear plate morphologies were obtained as shown in Fig. 6(b) and (c). Similar plate-like crystals were also obtained by the reactions of Zn(OH)2 with other straight chain organic oxychlorides. The plate-like morphologies were quite similar to those of LDHs.23,24 By contrast, the reaction product of Zn(OH)2 with benzoyl chloride had a fibrous morphology as shown in Fig. 6(d). A TEM image of the reaction product of Zn(OH)2 with benzoyl chloride indicates that the fibrous compound was a layered compound as shown in Fig. 7. The reaction products of Zn(OH)2 with phenylacetyl chloride and p-phenylazoben- Fig. 7 TEM images (500 000 ×magnification) of the reaction product zoyl chloride were not fibrous although their structures are of Zn(OH)2 with benzoyl chloride.similar to that of benzoyl chloride. The distance between Zn centres of the inorganic layer and the benzene ring in Conclusions C6H5CH2CO2–Zn bond was larger than that in C6H5CO2–Zn. However, the distance between Zn of the inorganic layer and We have established a preparation method of organic– inorganic layered compounds by the reaction of Zn(OH)2 the benzene ring of C6H5NNC6H4CO2–Zn was the same as that for C6H5CO2–Zn.The molecular length of p-phenylazo- with various organic oxychlorides. The IR spectra of the reaction products of Zn(OH)2 with organic oxychlorides indi- benzoyl chloride (1.16 nm) is about twice as large as that of benzoyl chloride (0.54 nm). These results suggest that steric cated the formation of CO2–Zn bonds. 40–98% of OH groups reacted with the organic compounds. SEM images showed repulsion between organic moieties between layers is important in determining the morphology. that the structures of the reaction products were plate-like, 2816 J. Mater. Chem., 1998, 8, 2813–28177 M.Inoue, H. Kominami, Y. Kondo and T. Inui, Chem. Mater., whereas that of the reaction product with benzoyl chloride 1997, 9, 1614. was fibrous. These results suggest that the structure of the 8 F. Cavani, F. Trifiro and A. Vaccari, Catal. Today, 1991, 11, 173. nanomaterial depends on the structures of the organic com- 9 H. Tagaya, S. Sato, H. Morioka, M. Karasu, J. Kadokawa and pounds incorporated.Chemical surface modification of inor- K. Chiba, Chem.Mater., 1993, 5, 1431. ganic compounds has been studied extensively to change 10 H. Tagaya, S. Sato, T. Kuwahara, M. Karasu, J. Kadokawa and K. Chiba, J. Mater. Chem., 1994, 4, 1907. their chemical and/or physical properties in a controlled 11 H. Tagaya, T. Kuwahara, S. Sato, M. Karasu, J. Kadokawa and manner.25,26 The present work describes a viable preparation K.Chiba, J. Mater. Chem., 1993, 3, 317. method of surface-modified inorganic layered compounds. 12 H. Tagaya, A. Ogata, T. Kuwahara, S. Ogata, M. Karasu, Organic intercalation compounds of smectite clays are known J. Kadokawa and K. Chiba, Microporous Mater., 1996, 7, 151. as organic sorbents and since the interlayer space of surface 13 T.Kuwahara, H. Tagaya and K. Chiba, Microporous Mater., modified Zn(OH)2 is hydrophobic the hybrid materials have 1995, 4, 247. 14 H. Morioka, H. Tagaya, M. Karasu, J. Kadokawa and K. Chiba, potential as shape-selective sorbents and catalysts. The method J. Solid State Chem., 1995, 117, 337. is also useful for controlling the organization of organic 15 H. Tagaya, H.Morioka, M. Karasu, J. Kadokawa and K. Chiba, molecules in the solid state, and preparation of microporous Supramol. Sci., 1995, 2, 33. materials which have controlled morphology. 16 T. Kubo, K. Uchida, K. Tsubosaki and F. Hashimi, Kogyo Kagaku Zasshi, 1970, 73, 75; Chem. Abstr., 1970, 73, 41407p. 17 H. Tagaya, S. Ogata, H. Morioka, J. Kadokawa, M. Karasu and Acknowledgments K.Chiba, J. Mater. Chem., 1996, 6, 1235. 18 M. Meyn, K. Beneke and G. Lagaly, Inorg. Chem., 1990, 29, 5201. 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O’Hare, Wiley, Chichester, 2nd edn., 1996, p. 171. Chemical Society, Washington, 1995. 3 A. Clearfield, in Progress in Intercalation Research, ed. 26 E. F. Vansant, P. Voort, and K. C. Vrancken, Characterization and W. M. Warmuth and R. Scho� llhorn, Kluwer, Dordrecht, 1994, Chemical Modification of the Silica Surface, Elsevier, New York, p. 223. 1995. 4 H. E. Katz, Chem.Mater., 1994, 6, 2227. 5 M. E. Thompson, Chem. Mater., 1994, 6, 1168. 6 J. J. Tunney and C. Detellier, J. Mater. Chem., 1996, 6, 1679. Paper 8/04557G J. Mater. Chem., 1998, 8, 2813–2817 28