assigned to the stretching vibration of theC=Nbond (imine bond).Two other newbandsappear at 1,680 and 1,607 cm-1 which are due to the remaining aldehyde C=O groupand the stretching vibration of C=C bonds of the phenyl ring, respectively.The presence of the chiral half unit of salen anchored on silica can be shown(Fig. 3, curve d) by the disappearance of the band at 1,680 cm-1 due to thesubsequent condensation of the remaining aldehyde C=O group with one amino group in the (1R,2R)-(-)-1,2-diaminocyclohexane chiral auxiliary. This is supportedby the increase of the intensity of the band assigned to the stretchingvibration of the C=N bond and the appearance of a new band at 1,390 cm-1 due toC–N stretching frequency.The comparison of the spectra of the free chiral salen ligand and sample 7 showedevidence of the immobilization of the chiral salen ligand over the support (Fig. 3,curves e and f), since the three most characteristic bands of the free chiral salen ligandappeared in IR spectrum of silica supported chiral salen ligand. These bands areattributed to C–N stretching frequency at 1,390 cm-1 and to the stretching vibrationsof C=N and C=C bonds which are slightly shifted from 1,630 and 1,595 cm-1 to1,640 and 1,607 cm-1, respectively, for the immobilized chiral salen ligand.On coordination of the immobilized chiral salen ligand to the vanadyl group, thecharacteristic bands of the metal salen complex appearing at 1535, 980 and561 cm-1 are assigned to the stretching frequency of C=N, V=O and V–N bands,respectively (Fig. 4). These bands are absent in the free and immobilized chiralsalen ligand (Fig. 4, curve c) but can be clearly observed for the VO(salen)complexes either free (Fig. 4, curve a) or anchored on the silica (Fig. 4, curve b).The solid reflectance UV–vis spectrum (Fig. 5) also supported successfulcoordination of the immobilized salen ligand with the vanadyl group, since thespectrum of the VO(salen) complex supported on silica (curve b) is similar to that ofthe homogeneous complex (curve a). The characteristic charge transfer bands ofhomogenous VO(salen) complex are present in the immobilized complex spectrum,but the bands are slightly shifted from 360, 390 and 412 nm to 368, 394 and417 nm, in order. The d–d transition band near 630 nm was also observed in theimmobilized complex spectrum though with a lower resolution than that for thetransmission spectrum of homogenous VO(salen) complex.The N2 adsorption–desorption isotherms and the corresponding BJH pore sizedistributions based on the desorption branch for the silica samples are shown in Figs. 6and 7. The nitrogen isotherm of the untreated silica sample shows a sharp capillarycondensation step at a relative pressure from 0.7 indicating a mesoporous structure ofthe silica with a uniform pore size distribution. Compared to the untreated silicamẫu, silica ngành aminopropylsilyl và Si–VO(salen) cho thấy một quan trọngthay đổi trong theN2 hấp phụ-desorption isothermand phân phối kích thước lỗ chân lông. Alớn giảm diện tích bề mặt đặt cược được quan sát thấy ngày functionalization của lầnsilica, với một sự giảm trong đường kính lỗ chân lông và khối lượng lỗ chân lông, gợi ý rằngVo(salen) phức tạp là mặt bên trong các lỗ chân lông của các tài liệu hỗ trợ (xem bảng 1)
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