New preparation method for surface-modified inorganic layered compounds Hideyuki Tagaya, * Sumikazu Ogata, Hiroyuki Morioka, Jun-ichi Kadokawa, Masa Karasu and Koji Chiba Department of Materials Science and Engineering, Yamagata University, Yonezawa, Yamagata 992, Japan New surface-modified inorganic layered compounds have been prepared by the reaction of Zn(OH), with organic oxychlorides in which 71-98% of the OH groups reacted. Their layered structures are similar to those of the layered double hydroxides (LDHs). Although LDHs have cationic charges, the reaction products are uncharged. The interlayer spacings of the reaction products were 8.3-14.8 A for the products of Zn(OH), with dioxychlorides, and 11.9-16.7 A for the reaction products of Zn(OH), with monooxychlorides, depending on the lengths of the organic compounds. The incorporation of a molecule into a crystalline inorganic host lattice to form an intercalation compound can lead to ordered materials.',2 It has been well reported that metal phosphonates are useful for organizing molecules into lamellar structure^.^ They are very similar to those formed by Langmuir-Blodgett (LB) techniques, but have better thermal stabilities than LB films.4 Recently we have prepared surface- modified inorganic layered compounds in which the surface of a Zn/Al layered double hydroxide (LDH) was modified by reaction with organic o~ychloride.~ The resulting compound is a well organized inorganic-organic hybrid.LDHs are inor- ganic layered compounds6 and many organic intercalates into LDHs are known.'-'' LDH layers are positively charged, therefore LDHs are anion-exchangeable clays.Surface-modi- fied LDHs also have anionic compounds between the layer^.^.'^ In this communication, we have prepared new surface-modified inorganic layered compounds in which a neutral amorphous compound, Zn(OH),, was reacted with an organic oxychloride as shown in Fig. 1. Both dioxychlorides and monooxychlorides reacted with Zn(OH), giving surface-modified layered com-pounds. The products differed from the surface-modified Zn/Al LDHs because they do not need to include any anionic compound between the layers. No clear peaks were observed in the XRD patterns of Zn(OH), as received, as shown in Fig.2(a). By the reaction of a small excess of amorphous Zn(OH), with sebacoyl chloride Fig. 1 Reaction of Zn(OH), with organic dioxychlorides to give inorganic-organic hybrid layered compounds 10 20 2Bldegrees Fig.2 XRD patterns of (a) Zn(OH),, and the reaction products of Zn(OH), with (b)adipoyl chloride, (c) suberoyl chloride, (d) sebacoyl chloride and (e)hexanoyl chloride [ClCO(CH,),COCl] in acetonitrile, a crystalline product was obtained. The XRD peaks of the reaction product were different from those of sebacoyl chloride and sebacic acid, and were rather similar to those of the surface-modified Zn/Al LDH after reaction with sebacoyl chloride. Similar XRD peaks to those of the surface-modified Zn/Al LDHs were observed in the reaction products of Zn(OH), with various kind of oxychlo- rides.SEM images indicate that clear plate crystals were obtained by the reaction of Zn(OH), with suberoyl chloride as shown in Fig. 3. Similar plate-like crystals were obtained for all the reaction products of Zn(OH), with various kinds of organic oxychlorides. The plate crystals were quite similar to those of the LDHs.l3,I4 The OH absorption at ca. 3500 cm-' in the IR spectrum of Zn(OH), was decreased markedly by the reaction with sebacoyl chloride as shown in Fig. 4(c). Peaks at ca. 1540 and 1465 cm-' indicate the formation of COO-Zn bonds. These results indicate that Zn(OH), reacted with organic oxychlorides giving surface-modified layered compounds. An excess of organic oxychloride was reacted with Zn(OH), in acetonitrile solution.Upon evaporation of the acetonitrile, a powder was obtained. The IR spectrum of the powder suggests the presence of surface-modified Zn(OH), and car- boxylic acid. However, clear XRD peaks of surface-modified J. Mater. Chem., 1996, 6(7), 1235-1237 1235 Fig. 3 $EM images (16000 x magnification) of (a)Zn(OH), and (b)the reaction product of Zn(OH), with suberoyl chlonde layered compounds were not obtained. It was considered that the first step of the reaction involving monooxychlorides (RCOCl) was a dehydration reaction between the OH groups of Zn(OH), and RCOC1, giving RCOO-Zn-OCOR. The cross-sectional Frea of one OH -Zn-OH unit15 was calcu- lated to be 9.6 A2. The layered structure was considered to be assembled by gathering RCOO-Zn-OCOR units.The svr- face area of an RCOO-Zn-OCOR unit is larger than 9.6 A2; therefore, an excess amount of RCOO-Zn- OCOR might interfere with the assembly of the layered structure owing to steric repulsion. As shown in Table 1, about 75% of the OH groups of Zn(OH), reacted with sebacoyl chloride to assemble a layered structure, while 71-74% of the OH groups reacted with dioxychlorides and monooxychlorides, except for products from reactions with small oxychlorides. In the cases of adipoyl chloride and n-butanoyl chloride, 98 and 85% of the OH groups reacted, respectively, probably because of the relatively small steric repulsion. The interlayer spacings (d) of the reaction products from dioxychlorides, 1236 J.Muter. Chem., 1996, 6(7), 1235-1237 4000 3000 2000 1000 wavenumber/cm-l Fig. 4 IR spectra of (a)Zn(OH),, (b)the reaction product of Mg(OH), with sebacoyl chloride, and the reaction products of Zn(OH), with (c) sebacoyl chlonde and (d)hexanoyl chloride Zn(OH),(O -G -0),, increased with increasing methylene chain length, and the same trend was observed in the case of the reaction products from monooxychloride, Zn(OH),(O-G),. However, the interlayer spacings of Zn(OH),(O-G), were larger than those of Zn(OH),(O-G-0),, considering their sizes, which indicates the bilayer structure of the reaction products from monooxy- chlorides. The interlayer spacings and the large y values in Zn(OH),(O-G-0), suggest the presence of bridging struc- tures as shown in Fig.1. We have already reported that water-treated Zn/Al LDHs react with organic oxychloride to give a surface-modified LDHs.' They were different from those of intercalation com- pounds of organic carboxylate anion^.'^,'^ By the reaction of sebacic acid wit! calcined LDH, the interlayer spacing increased to 18.8 A ts shown in Table 1, which is larger than the spacing of 12.8 A for the surface-modified LDH and the reaction product obtained in this study. However, we could not obtain water-treated Mg/A1 LDH and could not achieve surface modification of the Mg/A1 LDH. In this study, we also reacted Al(OH), and Mg(OH)2 with organic oxychlorides. Al(OH), did not react with organic oxychloride, while in the case of Mg(OH)2, the IR spectrum indicated that some of the Mg(OH)2 reacted with organic oxychloride.However, the decrease of the 0-H absorption of Mg(OH)2 was fairly small and clear peaks in XRD patterns were not observed. These results correspond to the facts that surface-modified Zn/Al LDH was obtained but surface-modified Mg/Al LDH was not obtained. The interlayer spacings of the surface-modified Zn(OH), obtained in this study were similar to those of the surface- modified LDHs with organic oxychlorides, probably because the size of aluminium metal is similar to that of zinc metal. We have already shown that LDHs have the ability to recognize the nuclear isomers of naphthalenecarboxylate ions.' Chemical surface modification of inorganic compounds have been studied extensively to change their chemical and/or physical properties in a controlled wa~.'~''~ The present study offers a new preparation method of surface-modified inorganic Table 1 Preparation of surface-modified inorganic layered compounds, Zn(OH),(O-G-0), or Zn(OH),(O-G), by the reaction of Zn(OH), with organic oxychlorides acid chloride n size/A d in XRoD OH-LDH LDH Zn (OH )z X Y Z of acid/A ClCO (CH,),COCI 4 6.4 6.8 7.8 14.8 8.3 0.04 0.98 -(C, 34.10; H, 3.83%) -6 8.9 8.9 10.7 10.8 0.54 0.73 (C, 34.89; H, 4.29%) 8 11.4 11.2 12.8 18.8 12.8 0.50 0.75 -(C, 40.50; H, 5.41%) 10 14.0 13.8 15.2 14.8 0.52 0.74 -(C, 43.82; H, 6.04%) CH,(CH,),COCI 2 4.7 -11.8 11.9 0.31 -1.69 (C, 32.94; H, 4.80%) 4 7.2 -16.1 16.7 0.58 -1.42 (C, 42.80 H, 6.49%) layered compounds which have potential as shape-selective sorbents and catalysts.The method is also useful for controlling the organization of organic molecules in the solid state, leading to new photofunctional materials in which various photo- responsive compounds are bonded or included between the layers. 8 9 10 11 H. 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