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In Situ Complex Formation of Long-Chain Schiff Bases with Silver(I) Ion in Monolayers and Their Langmuir-Blodgett Films Minghua Liu,* Gang Xu, Yaohu Liu, and Qian Chen Laboratory of Colloid and Interface Science, Center for Molecular Science, Institute of Chemistry, 100080, Beijing, China Received July 17, 2000. In Final Form: October 6, 2000 The in situ complex formation between two novel long-chain Schiff bases with Ag(I) ion at the air/water interface and their transferred Langmuir-Blodgett films were investigated. The long-chain Schiff bases containing heteroaromatic benzimidazole (BSC18) and benzthiazole (TSC18) rings form stable monolayers at the air/water interface. Addition of AgNO3 in the subphase caused the complex formation of the Schiff base with Ag(I). The Schiff base containing benzthiazole group formed a 1:1 complex with Ag(I). Regular layer structures are formed in the LB films of the Schiff base ligand and Ag(I) complex. The TSC18-Ag(I) complex showed orange color, which was specific only for the combination of TSC18 and Ag(I). X-ray photoelectron spectrum (XPS) of the transferred LB film revealed that a 1 (BSC18):2 (Ag(I)) complex was formed in the case of BSC18, which was explained by the coordination of Ag(I) ion with imine and OH and with benzimidazole. While the LB film of BSC18 showed a well-defined layer structure, that of the Ag(I) complex did not.
Introduction Monolayer and Langmuir-Blodgett techniques are among the powerful means to control the molecular orientations and packing at the molecular level.1,2 Supramolecular assemblies of metal complexes constructed by these methods are of considerable interest due to their fascinating optical,3-6 electrical,7,8 photoelectrical,9,10 magnetic,11-13 and catalytic14,15 properties. While amphiphilic metal complexes are usually used to construct monolayers and Langmuir-Blodgett films, regulation of coordination at the air/water interface also appears to be valuable and effective. This latter method utilized the coordination of ligand in the monolayers and metal ions in the subphase. Some interesting properties of monolayers are expected using this method. A number of amphiphiles functionalized with organic ligands such as crown ethers,16 (1) Roberts, G. G.; Langmuir-Blodgett Films; Plenum: New York, 1990. (2) Ulman, A. An Introduction to Ultrathin Organic Films; Academic Press: New York, 1991. (3) Schick, G. A.; Schreiman, I. C.; Wagner, R. W.; Lindsy, J. S.; Bocian, D. F. J. Am. Chem. Soc. 1988, 111, 1344. (4) Zhang, R. J.; Yang, K. Z. Langmuir 1997, 13, 7141. (5) Taniguchi, M.; Ueno, N.; Okamoto, K.; Karthaus, O.; Shimomura, M.; Yanagishi, A. Langmuir 1999, 15, 7700. (6) Yam, V. W.-W.; Yang, Y.; Yang, H.-P.; Cheung, K.-K.; Organometallics 1999, 18, 5252. (7) Nakamura, T.; Kojima, K.; Matsumoto, M.; Tachibana, H.; Tanaka, M.; Kawabata, Y. Chem. Lett. 1989, 367. (8) Xiao, Y.; Yao, Z.; Jin, D. Thin Solid Films 1993, 223, 173. (9) Xia, W.-S.; Huang, C. H.; Zhou, D. J. Langmuir 1997, 13, 80. (10) Taniguchi, T.; Fukasawa, Y.; Miyashita, T. J. Phys. Chem. B 1999, 103, 1920. (11) Poertz, M.; Dacal, F.; Segmuller, A. Phys. Rev. Lett. 1978, 10, 246. (12) Byrd, H.; Pike, J. K.; Talham, D. R. J. Am. Chem. Soc. 1994, 116, 7903. (13) Aiai, M.; Ramos, J.; Mingotaud, C.; Amiell, J.; Delhaes, P.; Jaiswal, A.; Singh, R. A.; Singh, B.; Singh, B. P. Chem. Mater. 1998, 10, 728. (14) Maassen, E.; Tieke, B.; Jordan, G.; Rammensee, W. Langmuir 1996, 12, 5595. (15) To¨llner, K.; Popovitz-Biro, R.; Lahav, M.; Milstein, D. Science 1997, 278, 2100. (16) Mun˜oz, S.; Malle´n, J.; Nakao, A.; Chen, Z.; Gay, I.; Echegoyen, L.; Gokel, G. W. J. Am. Chem. Soc. 1993, 115, 1705.
cyclam,17 dithiocarbamate,18 imidazole,19 calixarenes,20,21 iminodiacetate,22 pyridine,23 8-hydroxyquinoline,24 benzothiazolium styryl,25 and o,o′-dihydroxyazobenzene26 have been used to construct monolayers and LB films of metal complexes by taking advantage of the coordination reaction at the air/water interface. We have been interested in the in situ formation of metal complexes at the air/water interface. To date, we have synthesized a series of amphiphiles containing organic ligands such as imidazole,27 benzimidazole,28 2-(2-thiazolylazo)resorcinol (TAR),29a and 2-(2-pyridylazo)resorcinol (PAR)29d and investigated their complex formation at the air/water interface. Some interesting properties such as ion recognition,29a silver(I) ion induced monolayer formation,28 (17) (a) Kunitake, T.; Ishikawa, Y.; Shimomura, M.; Okawa, H. J. Am. Chem. Soc. 1986, 108, 327. (b) Ishikawa, Y.; Kunitake, T.; J. Macromol. Sci.-Chem. 1990, A27, 1157. (18) (a) Bdach, W.; Ahuja, R. C.; Mo¨bius, D.; Schrepp, W. Thin Solid Films 1992, 210/211, 434. (b) Budach, W.; Ahuja, R. C. Mo¨bius, D. Langmuir 1993, 9, 3093. (19) (a) van Esch, J. H.; Stols, A. L. H.; Nolte, R. J. M. J. Chem. Soc., Chem. Commun. 1990, 1658. (b) van Esch, J. H.; Nolte, R. J. M.; Ringsdorf, H.; Wildburg, Langmuir 1994, 10, 1955. (20) Ishikawa, Y.; Kunitake, T.; Matsuda, T.; Otsuka, T.; Shinkai, S. J. Chem Soc., Chem. Commun. 1989, 736. (21) Moreira, W. C.; Dutton, P. J.; Aroca, R. Langmuir 1995, 11, 3137. (22) (a) Shnek, D. R.; Pack, D. W.; Sasaki, D. Y.; Arnold, F. H. Langmuir 1994, 10, 2382. (b) Ng, K.; Pack, D. W.; Sasaki, D. Y.; Arnold, F. H. Langmuir 1995, 11, 4048. (23) Werkman, P. J.; Schouten, A. J.; Noordegraff, M. A.; Kimkes, P.; Sudhoelter, E. J. R. Langmuir 1998, 14, 157. (24) (a) Ouyang, J. M.; Tai, Z. H.; Tang, W. X. Thin Solid Films 1996, 289, 199. (b) Ouyang, J. M.; Li, C.; Ling, W. H.; Zheng, W. J. J. Chem. Res. 1999, 4, 276. (25) Lednev, I. K.; Petty, M. C. J. Phys. Chem. 1994, 98, 9601; 1995, 99, 4176. (26) Hwang, M. J.; Jeung, C. S.; Suh, J.; Kim, K. J. Colloid Interface Sci. 1999, 216, 96. (27) Liu, M. H.; Kira, A.; Nakahara, H.; Fukuda, K. Thin Solid Films 1997, 295, 250. (28) Liu, M. H.; Kira, A.; Nakahara, H. Langmuir 1997, 13, 4807. (29) (a) Liu, M. H.; Kira, A.; Nakahara, H. Langmuir 1997, 13, 779. (b) Liu, M. H.; Ushida, K.; Kira, A.; Nakahara, H. J. Phys. Chem. B 1997, 101, 1101. (c) Liu, M. H.; Ushida, K.; Kira, A.; Nakahara, H. Thin Solid Films 1998, 327-329, 491. (d) Liu, M. H.; Ushida, K.; Kira, A.; Nakahara, H. Adv. Mater. 1997, 9, 1099.
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Figure 1. Synthetic scheme of the long-chain Schiff bases and their abbreviations.
and photoaccelerated coordination in the LB films29c,d have been found. Schiff bases are important ligands in coordination chemistry, as they form stable complexes with many transition metal ions.30,31 Langmuir-Blodgett films of amphiphilic Schiff base complexes have been investigated and interesting features were revealed,32-34 however, these investigations mainly concerned the metal complexes of Schiff bases themselves. In this paper, as a part of our continuous work on the coordination regulation at the air/water interface, we report the in situ metal complex formation of two novel long-chain Schiff bases with Ag(I) ion in the subphase. The long-chain Schiff bases were synthesized as shown in Figure 1. These compounds differ from previously investigated TARC18 where azo group was contained, while in present compounds, azomethene group was contained. The complex formation at the air/ water interface and in the LB films was verified by π-A measurement, UV-vis absorption spectra, XPS, and FTIR spectra of the LB films, and the layer structures of the LB films were investigated by using XRD. Experimental Section Materials. The starting materials 2,4-dihydroxybenzaldehyde, octadecyl bromide, 2-aminobenzimidazole, and 2-aminobenzthiazole were purchased from Tokyo Kasei. Chloroform and ethanol were from Peking Chemicals and distilled before use. Syntheses of the long-chain Schiff bases were performed as shown in Figure 1. 2-hydroxyl-4-octadecyloxybenzaldehyde was synthesized from 2,4-dihydroxybenzaldehyde and octadecyl bromide by a modified literature method:35 2,4-dihydroxybenzaldehyde was refluxed with 1 mol equiv of octadecyl bromide and KOH in ethanol for 24 h. The ethanol was removed and the resultant was washed with water and recrystallized from hexane, mp 64 °C. The target amphiphilic long-chain Schiff bases BSC18 and TSC18 were synthesized by the condensation of 2-hydroxyl4-octadecyloxybenzaldehyde with 2-aminobenzimidazole and 2-aminobenzthiazole in ethanol solution, respectively. The 1H NMR and elemental analysis data of the two compounds are as follows. 2-(2′-Benzimidazolyliminomethyl)-4-octadecyloxyphenol (BSC18): mp:168-169 °C; 1H NMR (300 MHz, CDCl3) δ (ppm) 0.88 (t, 3 H), 1.26 (m, 30 H), 1.83 (m, 2 H), 3.99 (t, 2 H), 6.54 (m, 2 H), 7.28 (m, 2 H), 7.39 (m, 2 H), 7.70 (d, 1 H), 9.13 (s, (30) Schiff, H. Justus Liebigs Ann. Chem. 1869, 150, 193. (31) Pfeiffer, P.; Buchholz, E.; Bauer, O. J. Prakt. Chem. 1931, 129, 163. (32) Sundari, S. S.; Dhathathreyan, A.; Kanthimathi, M.; Nair, B. U. Langmuir 1997, 13, 4923. (33) Vijayalakshmi, R.; Dhathathreyan, A.; Kanthimathi, M.; Subramanian, V.; Nair, B. U.; Ramasami, Langmuir 1999, 15, 2898. (34) Nagel, J.; Oertel, U.; Friedel, P.; Komber, H.; Mo¨bius, D. Langmuir 1997, 13, 4693. (35) Menczel, J. D.; Leslie, T. M. Thermochim. Acta 1990, 166, 309.
Figure 2. π-A isotherms of the BSC18 (A) and TSC18 (B) monolayers on water (a) surface and the subphase containing 1 mM AgNO3 (b). br, 1 H), 9.47 (s, 1 H), 12.76 (s, 1 H). Calcd for C32H47N3O2: C, 76.00; H, 9.37; N, 8.31. Found: C, 75.98; H, 9.48; N, 8.25. 2-(2′-Benzthiazolyliminomethyl)-4-octadecyloxyphenol (TSC18): mp 121-122 °C; 1H NMR (300 MHz, CDCl3) δ (ppm) 0.88 (t, 3 H), 1.26 (m, 30 H), 1.81 (m, 2 H), 4.03 (t, 2 H), 6.56 (m, 2 H), 7.37 (m, 2 H), 7.50 (m, 1 H), 7.83 (d, 1 H), 7.95 (d, 1 H), 9.16 (s, 1 H), 12.68 (s, 1 H). Calcd for C32H46N2O2S: C, 73.52; H, 8.87; N, 5.36. Found: C, 73.31; H, 8.88; N, 5.10.
Procedures Monolayers of the compounds were formed by spreading chloroform solutions (3 × 10-4 M) onto the water surface or the subphases containing silver(I) nitrate. After allowing 10 min for the evaporation of the solvent, surface pressure-area isotherms were recorded using a KSV film balance with a compressing speed of 5 cm2/min. AgNO3 was recrystallized from methanol. Millipore Q (18 MΩ cm) water was used in all cases. LB films were deposited by using a horizontal method. Quartz, ordinary glasses, and glasses coated with ITO were used to deposit the films for UV-vis, X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS) measurements, respectively. Silicon plates (cleaned with a mixture of concentrated H2SO4 and H2O2) were used to deposite the film for FT-IR measurements. UV spectra were recorded with a Shimazu-PC 1601 system. XRD was recorded on a Rigaku system. XPS were measured with a VG Scientific ESCALAB220I-XL spectrometer using Mg KR as the excitation source (h 1253.6 eV). FT-IR transmittance spectra were recorded with a Bio-Rad FT-IR spectrometer. Results and Discussions Surface Pressure-Area Isotherms. The surface pressure-area (π-A) isotherms of the two compounds on water surface and the subphase containing AgNO3 are shown in Figure 2. In the case of BSC18, the onset of the surface pressure is observed at 0.45 nm2/molecule, and the monolayer is a typical condensed-type monolayer. When AgNO3 was added to the subphase, although the onset of the surface pressure appears at the same position, the curve becomes steeper. By extrapolating the linear part of the curve to zero surface pressure, a limiting area of 0.36 and 0.38 nm2/molecule can be obtained for the monolayer on pure water and AgNO3 subphase, respectively. Considering the molecular dimensions of the headgroup using the CPK model, it is suggested that the headgroup is orientated with its long axis nearly vertical to the water surface. The slight increase of the limiting area of the BSC18 monolayer on the AgNO3 subphase
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Figure 4. XPS spectra of 40-layer LB films on an ITO glass plate of TSC18 and BSC18 transferred from the monolayers on 1 mM AgNO3 subphase at 30 mN/m.
Figure 3. UV-vis spectra of BSC18 (A) and TSC18 (B) in methanol solution (a), and LB films transferred from the water surface (b) and the subphase containing 1 mM AgNO3 (c).
implies complex formation between the monolayer and AgNO3 in the subphase. Similar monolayer formations of TSC18 on water and the subphase containing AgNO3 were observed. A slight increase of the limiting area of the monolayer on the AgNO3 compared to that on the pure water interface is observed, suggesting complex formation in the case of TSC18. Langmuir-Blodgett Films. UV-Vis Spectra of the LB Films. The above-formed monolayer can be transferred by the horizontal lifting method onto solid substrates such as quartz, glass, ITO-coated glass, and silicon, and the properties of the transferred films were investigated. Figure 3 shows the UV-vis spectra of the LB films (40 layers on quartz plate) transferred at 25 mN/m from the water surface and the subphase containing AgNO3 for BSC18 (A) and TSC18 (B), respectively. For comparison, the spectra of the corresponding compounds in methanol solution are also shown. Three bands are observed at 248, 289, and 374 nm for BSC18 in methanol (Figure 3a). The band at 374 nm can be regarded as the charge-transfer band through the imine group. The band at 248 nm can be regarded as localized at the benzimidazole ring.36 The band at 289 nm is due to the conjugation of the aromatic rings. When the monolayer was transferred onto a solid substrate to form an LB film, the band at 374 nm in solution showed a large blue shift to 335 nm, while the other two bands showed only a slight blue shift. Since the band at 374 nm is related to the long-axis of the headed aromatic rings, this blue shift indicates that headgroups are nearly vertically orientated to the substrates in the LB films, i.e., an H-aggregate is formed in the LB film of BSC18. Kawamura et al have also reported such kind of large blue shift of the LB films of a long-chain salicyli(36) Krishnamyrthy, M.; Phaniraj, P.; Dogra S. J. Chem. Soc., Perkin Trans. II 1986, 1917.
deneaniline derivative.37 When the monolayer was transferred from the subphase containing AgNO3, the UV-vis spectrum changed significantly. Only two distinct bands at 356 and 298 nm are observed, while a shoulder appeared at 250 nm. The band at 248 nm is related to the benzimidazole ring. Its disappearance indicates the deprotonation of the benzimidazole ring and suggests that a complex was formed between the benzimidazole ring and Ag(I). This is in accordance with our previous results with benzimidazole derivatives.28 The LB films of TSC18 from the water surface and the subphase containing AgNO3 showed very distinct changes. The film from the water surface is pale yellow, while the film from the aqueous AgNO3 subphase is orange. Spectral changes were measured. The LB film from the water surface showed a slight blue shift (from 383 nm in methanol solution to 376 nm in LB film). For the monolayer transferred from the AgNO3 subphase, a new band appeared at 466 nm. The color change implies complex formation of TSC18 with AgNO3. Moreover, the color change is specific, only the combination of silver ion and TSC18 can cause such a of color change. XPS Study. From the above discussion, it is obvious that there is some interaction between the monolayers of TSC18 and BSC18 with AgNO3 in the subphase. To quantitatively characterize such complexes formed in the monolayers, the XPS spectra of the transferred LB films were measured. Figure 4 shows the XPS spectra of a 40layer BSC18 LB film on ITO glass transferred at 30 mN/ m.. The binding energies are observed at 286.0 (C1s), 400.2 (N1s), 534.0 (O1s), 369.6 (Ag3d5/2), and 375.9 (Ag3d3/2) eV. Careful investigation on the N1s region showed that no N1s band was observed at around 407 eV, the electrostatic binding energy of the nitrate anion.38 These spectral features indicate that only silver cation and not nitrate anion was incorporated into the monolayer. In the case of TSC18, the C, N, O, and Ag(I) binding energies were observed at 280.0 (C1s), 400.2 (N1s), 534.1 (O1s), and 375.5 eV (Ag3d3/2), respectively, and a binding energy of S2p was observed at 165.5 eV. The latter binding energy corresponds to the binding energy of S in heteroaromatic rings. A further, careful survey on the N1s region revealed a weak binding energy at 407 eV besides the strong band at 400.2 eV. This indicates that in addition to the Ag(I) ion, a small amount of AgNO3 was incorporated into the TSC18 monolayer. Quantitative analysis of the XPS spectra of the two films indicate that BSC18:Ag(I) ) 1:1.99, while TSC18:Ag(I) ) 1:1.20. This indicates that in the (37) Kawamura, S.; Tsutsui, T.; Saito, S.; Murao, Y.; Kina, K. J. Am. Chem. Soc. 1988, 110, 509. (38) Chong, D. P.; Herring, F. G.; McWilliam, D. J. Chem. Phys. 1974, 61, 78.
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Figure 6. X-ray diffraction patterns of the LB films of BSC18 (A) and TSC18 (B) from water (a) and 1 mM aqueous AgNO3 solution (b)
Figure 5. FT-IR spectra of the LB films (50 layers on silicon at 30 mN/m) of BSC18 (B), and TSC18 (A) from water (a) and the subphase containing 1 mM AgNO3 (b).
case of BSC18, two Ag(I) ions were incorporated into the monolayer per BSTC18 molecule, while in the case of TSC18, more than one Ag(I) ion was incorporated into the LB film. From the structures of the two compounds, it is obvious that two coordination sites existed in BSC18, i.e., the benzimidazole moiety and the hydroxyl group, together with the imine group. In the case of TSC18, only the hydroxyl group and imine can take part in the coordination. Therefore, a 1:1 complex was formed with TSC18, and a 1 (ligand):2 (cation) complex was formed in the case of the BSC18 monolayer, as shown in Figure 7. In the case of TSC18, a slight excess of Ag(I) over the expected 1:1 complex was observed. This is attributed to the incorporation of AgNO3 into the TSC18 monolayer due to the strong interaction of S with Ag(I). FT-IR Spectra of the LB Films. From the above discussion, it can be deduced that Ag(I) complexes are formed in BSC18 and TSC18 monolayers. To further confirm such complex formation, the FT-IR spectra of the transferred LB films from the water surface and AgNO3 subphase were measured. Figure 5 shows the FT-IR spectra of the LB films in the region from 1000 to 1800 cm-1, which is sensitive to the complex formation. Main IR bands are observed at 1646, 1598, 1520, 1480, 1437, 1405, 1308, 1250, 1180, 1150, and 1108 cm-1. When the film was transferred from aqueous AgNO3 solution, IR bands changed to 1622, 1587, 1494, 1446, 1396, 1316, 1186, and 1108 cm-1. The band at 1646 cm-1 can be assigned to the CdN vibration, while the bands at 1598, 1520, and 1480 cm-1 can be assigned to the band of aromatic rings in the LB film of TSC18. When the TSC18 film was transferred from AgNO3, the CdN band shifted to 1620 cm-1, while those bands assigned to the aromatic rings shifted to lower frequencies of 1587, 1494, and 1446 cm-1. These spectral changes are in accordance with those reported elsewhere for Schiff bases before and after metal ion complexation to the imine groups.39 A strong band at 1250 cm-1 observed at TSC18 film from water can be (39) Teyssie, P.; Charette, J. P. Spectrochim. Acta 1963, 19, 1407.
assigned to δO-H. After complex formation, the band became very weak, indicating that OH was deprotonated. Similar behavior is observed for BSC18. On the other hand, the symmetric and antisymmetric vibration of CH2 is sensitive to the packing of the alkyl chains.40 In the case of TSC18 LB films, the CH2 symmetric and asymmetric vibration bands were observed at 2854 and 2922 cm-1, respectively, for the film from water, while they appear at 2862 and 2924 cm-1 for the film from AgNO3. In the case of BSC18, the CH2 vibrations were observed at 2918 and 2852 cm-1 for the film from water and at 2921 and 2855 cm-1 for the film from AgNO3. The lower frequencies of the CH2 stretching vibrations in the films from the water surface than those from the aqueous AgNO3 subphase indicate that alkyl chains are more vertically oriented in the former. This implies that during complex formation the vertical amphiphilic molecules tilted to the water surface due to complex formation. In addition, the alkyl chains packed more vertically in BSC18 LB films than in TSC18 films. XRD of the LB Films. To characterize the layer structure of the LB films, X-ray diffraction of the LB films transferred onto glass plates at 30 mN/m was measured Figure 6. For the film transferred from the water surface, two diffraction peaks are observed for TSC18 and BSC18. In the case of TSC18, diffraction peaks were at 2.06 and 8.71, corresponding to an interlayer distance of 4.28 nm. In the case of BSC18, the films showed two diffraction peaks at 2.9 and 5.4, corresponding to a long spacing of 3.39 nm. From the CPK model, the length of TSC18 and BSC18 was estimated to be 3.66 and 3.71 nm, respectively. These results indicate that BSC18 takes an X-type arrangement in the LB films. The layer distance of 3.39 nm corresponds to a vertical arrangement of molecules at the substrate considering the length of the headgroup and the length of the alkyl chain. This agrees with the UVVis spectra data, in which a large blue shift of the film was observed. In the case of TSC18, a distance of 4.28 nm is too long for a single-layer molecule, implying a doublelayered LB film was formed. In this case, the alkyl chain is rather tilted, which is in agreement with the above FT-IR results. Although we fabricated the films using the horizontal lifting method, which favors the X-type film formation, this type of change may be due to the overturn of the TSC18 LB film in the transfer process.41 On the other hand, for the TSC18 film transferred from the (40) Sapper, H.; Cameron, D. G.; Mantsch, H. H. Can. J. Chem. 1981, 59, 2543. (41) Kato, T. Chem. Lett. 1988, 1993.
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spectrum suggests that a 1:2 complex was formed for BSC18 on the subphase containing AgNO3. From the structure of the two compounds, it is possible that in the case of BSC18, benzimidazole, imine, and OH groups take part in the coordination, while in the case of TSC18, only the imine group and OH are result from complexation, as shown in Figure 7. TSC18 complex formation leads to the incline of the aromatic ring as a result of the decrease of the long spacing. In the case of BSC18, two kinds of complexes were formed, which may result in a disordered layer structure and therefore an absence of X-ray diffraction peaks. Conclusions
Figure 7. Possible complexes formed in the monolayers and their arrangements in monolayers.
subphase containing AgNO3, a layer distance of 3.04 nm was obtained. This is in accordance with the above FT-IR and UV-vis results. In the case of BSC18, however, no diffraction peak was found. As discussed above, the XPS
Two novel long-chain Schiff bases containing heteroaromatic benzimidazole (BSC18) and benzthiazole (TSC18) groups are found to form stable monolayers at the air/water interface with the molecules vertically oriented on the water surface. When the compounds were spread on an aqueous AgNO3 subphase, an in situ complex formation took place. In the case of the Schiff base containing benzthiazole (TSC18), a 1:1 complex was formed, while in the case of the Schiff base with benzimidazole (BSC18), a 1 (ligand):2 (Ag(I)) complex was formed. The complex between TSC18 and Ag(I) showed an orange color, which is specific only to the combination of TSC18 and Ag(I) ion. Acknowledgment. This work was supported by the National Natural Science foundation (Nos. 29992590-3 and 69881003) and Youth Fund of the Chinese Academy of Sciences (CAS, KJ952-J1-563). LA0010121
