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5.03;5.65(0H)(H-16), 2.54(H-17), 1.43(H-18), 0.56;0.22(H-19), 1.32(H-21), 3.10;1.68(H-22) 2.31;2.05(H-23) 3.89(H-24), 1.58(H-26) 1.30(H-27), 1.02(H-28), 1.96(H-29), 1.44(H-30) 5.42(H-1'-Glcp(1*2) Glcp), 4.13(H-2'), 4.24(H-3'), 4.30(H-4'), 3.95(H-5'), 4.50,4.44(H-6'), 4.99(H-1''-Glcp(1^3) Agl), 4.30(H-2''), 4.33(H-3''), 4.18(H-4''), 3.88(H-5"),4.53,4.37(H-6") [3].
Acid hydrolysis. 5 mg of counpound 3 had been hydrolyzed as its shown above. According to physical-chemical constants, and according to direct comparison with authentic samples, isolated compound 5 had been identified with cyclosiversigenin. In hydrolysate paper chromatography by comparison with authentic samples we had revealed xylose and glucose.
For NMR spectra 13C refer to table.
Cyclostipuloside D (4). C41H68014, melt. temp. 252-254 °C (from methanol), [a ]D + 30.0 + 20 (with 0.5; methanol).
IR spectrum (KBr, v, sm-1): 3391(OH), 3035 (cyclopropane group).
For NMR spectra :H and 13C refer to table.
Acid hydrolysis. 30 mg of compound 4 had been hydrolyzed in 30 ml of 0.5% solution of methanol solution H2S04 at 70 °C within 5 hours. Upon
distilled, precipitates had been filtered, dried and chromatographed on silicagel, eluting with a chloroform-methanol system (15:1). Herewith we had 8 mg of compound 6, C30H5005, with melt. temp. 228230 °C (ethyl acetate), IR spectrum (KBr, v, sm-1): :3420 (OH), 1648(C=C).
PMR spectrum of compound 6 (S, ppm., C5D5N, TMS): 0.92, 1.06, 1.13, 1.30, 1.34, 1.53 (6xCH3, s) h 1.46 (2xCH3, s), 3.08 (2H, q. 3J=11.9 Hz, H-22), 2.49 (1H, d. 3J=7.3 Hz, H-17), 3.88 (1H, d.d. 3J=8.9 and 4.4 hz, H-24), 5.08 (1H, q. J=6.6 Hz, H-16), 5.25 (1H, 9(11)- double compound, s).
For NMR spectra 13C refer to table.
Keeping elute the column with the same system, 12 mg of cyclosiversigenin has been isolated (5), C30H5005, with melt. temp. 239-240 °C (methanol), [aft +49.0±20 (from 1.37; methanol). IR spectrum (KBr, v, sm-1): 3396 (OH), 3035 (cyclopropane group).
Water solution has been heated within 3 hours, then neutralized with barium carbonate, residues had been removed, filtrate had been evaporated and chromatographed on paper in the butanol-pyridine-water system (6:4:3). Having compared with authentic samples we had revealed glucose and xylose.
cooling we fed 30 ml of water, methanol had been
References:
1. Кайпназаров Т. Н., Утениязов К. К., Качала В. В., Саатов З., Шашков А. С. Химия природ. соедин., 2002.- 228 с.
2. Кайпназаров Т. Н., Утениязов У К. К., Саатов З. // Тритерпеновые гликозиды Tragacantha stipulosa и их генины. Строение циклостипулозида Е. // Химия природ. соедин.- (1). 2004.- C. 35-38.
3. Утениязов К. К., Саатов З., Абдуллаев Н. Д., Левкович М. Г. Химия природ.соедин., 1998.- 509 с.
4. Кучербаев К. Дж., Утениязов К. К., Качала В. В., Саатов З., Шашков А. С., Утениязов К. У, Халмура-тов П. Химия природ. соедин., 2002.- 50 с.
5. Свечникова А. Н., Умарова Р. У, Горовиц М. Б., Сейтаниди К. Л., Рашкес Я. В., Ягудаев М. Р., Абуба-киров Н. К. Химия природ.соедин., 1981.- 67 с.
6. Bentley H. R., Henry I. A., Irvine D. S., Spring F. S. J. Chem. Soc., 1953.- 3673 p.
https://doi.org/10.29013/AJT-22-3.4-87-91
Toshpulatov D. T., Mirzaev Sh.E., Nasimov A. M., Yakubov B. A., Samiev A. A., Tashpulatov Kh. Sh., Samarkand State University, Uzbekistan
SYNTHESIS OF [CO(BPY)(SCN)J2+ COMPLEX AND ITS PHOTOCHEMICAL PROPERTIES IN THE SOL-GEL MATRIX
Abstract. Synthesis of [Co(bpy)(SCN)4]2+ complex carried and its photochemical properties studies explored in both organic solvent and tetraethoxysilane based sol-gel membrane. TEOS based sol-gel membrane shown suitable matrix and cobalt dye retain its photochemical properties inside the pores of membrane. Based on spectral changes in the sol-gel ma matrix, possible changes in molecular shape also discussed. Moreover, the sol-gel membrane confirm cobalt complex from photobleaching or degradation.
Keywords: complex, sol-gel matrix, TEOS, absorption, immobilization, MLCT band.
Introduction ior; (iii) light absorption in the visible spectral re-
Utilization of charge-transfer dye first com- gion; (iv) long-lived electronically excited states; menced when Brian O'Regan and Michael Gratzel (v) intense luminescence. These features made them
reported their revolutionary work in 1991 [1]. The general mechanisms for light-to-electrical power conversion in dye sensitizer solar cells as followed (i) light is absorbed by a sensitizer to form a molecular excited state; (ii) the excited state may inject an electron into the semiconductor thus causing charge separation; (iii) the oxidized sensitizer is "regenerated" by an external electron donor. Once the electron has performed useful work in the external circuit, it returns to a counter electrode where it reduces the oxidized electron donor. Hence the solar cell is termed "regenerative" as all oxidation chemistry at the dye-sensitized electrode is reversed at a dark counter electrode such that no net chemistry occurs.
It is known that Ru(ll) polypyridines or Ru(ll) complexes have been used as dye sensitizer widely because of remarkable advantages as: (i) ease of preparation; (ii) reversible electrochemical behav-
perfect choice for such systems.
Despite such favored features, there are obstacles related to Ru which is "well-known" being high cost (32% cheaper than gold), low abundant (78th most abundant element!) and toxic. Hereof one could concern to other alternatives than Ru(ll) polypyridines. Hereof one could concern to other alternatives than Ru(ll) polypyridines. One of alternative is copper(l) complexes which were found a possible solution for that issue [2-6]. Being a tetrahedrally symmetric, copper(l) shown very promising results with both homoleptic and heteroleptic ligands. Other preferred complexes were found to be cobalt(lI/ III) complexes [7-12]. If one compare the structure of copper(I) and cobalt(II/III) complexes, the former have unique tetrahedral (sometimes distorted) shape while cobalt complexes possess octahedral shape (Figure 1).
L
Cut
L- L
L
.......
T
d
JCoi
O,
Figure 1. Different coordination geometry of Cu+ and Co+2 complexes
In order to be practically useful, it is often required to immobilize molecule of interest in solid matrices. A number of papers dedicated to these issue ranging from composites to sol-gel membrane [13-16]. Immobilization not only maintains mechanical stability but also may shape of the photochemical properties of the dopant. Dye doped solid materials also found their application in catalysis and solar energy conversion systems [14-17]. The solgel technology possesses the following superiority: (i) the prepared nanoparticles have good uniformity (particle size distribution) and high purity, (ii) it is energy saving (because of temperature condition) and (iii) it can be used to prepare wide range of materials as coatings, fibers, and composite materials.
In this article we propose results of synthesis and immobilization of cobalt complex with unique photochemical properties. In order to find suitable environment for the synthesized dye, several matrices have been examined and the most favorable one is proposed.
Experimental
Materials and methods
Tetraethoxysilane (TEOS) was purchased from Haihang Industry Co., Ltd (PRC). All solvents: ethanol (EtOH), methanol (MetOH), acetoni-trile (CAN), tetrahydrofurane (THF), dimethyl-formamide (DMF), hexane (C6H), nitrobenzene (CH3NO2), acetone (CH3COCH3), benzene (C6H6), octane (CgH1g), toluene (C7H8) were analytical grade and used without any further purification. Cobalt(II) chloride hexahydrate (CoCl2 • 6H2O), 2,2-bipyridine (C10HgN2), ammonium thiocyanate (NH4SCN), hy-
drochloric acid (HCl) and nitric acid (HNO3) were chemical pure and used as received. All buffers and solutions prepared using chemical pure grade reactants and doubly distilled water used as solvent.
Synthesis of [Co(bpy)(SCN)4]2+
In order to obtain desired complex, 1 eqn. of CoCl2 • 6H2O, 1 eqn. of bipyridine and 4 eqn. of NH4SCN weighted. Namely, tuzidan 2,38 grams of CoCl2 • 6H2O, 1,56 grams bipyridine, 3,05 grams of NH4SCN mixed in 96% ethanol and completely dissolved. The reaction mixture was refluxed at 70 °C and stirred at 600 RPM for 3 hours. The temperature was increased gradually from the room temperature to 70 °C. After 3 hours, the solution was cooled 12 hours down to the room temperature and precipitation occurred. The precipitation was vacuum filtered and decanted with 96% ethanol for several times until to obtain pure compound. The purified precipitate was kept overnight at 80 °C in the drying oven (Memmert, Germany).
Immobilization of cobalt dye in sol-gel membrane
After several experiments on the condition of an optimal sol-gel cocktail content, the following ratio of components was chosen: TEOS, H2O, C2H5OH: HCl 1: 4: 4: 0,15 respectively in order to complete the hydrolysis reaction, the sol mixture was stirred for 30 minutes at the room temperature. Consequently cobalt complex solution in DMF was added dropwise and vigorously stirred another 3 hours. Solution of sol then remained for 24 hours in the ambient temperature for aging. Microscope slides were taken and cut into 0.6x4 cm pieces. All glasses were activated in the aqueous solution of nitric acid for 1 hour and rinsed with ethanol and copious amount of water before dip coating process. Coated slides were kept another 24 hours in the ambient temperature and dried at 70 °C overnight.
Spectroscopic studies of prepared membranes
The surface of the films was investigated using the light microscope Optika (Germany). UV-vis spec-
L
L
L
L
L
trophotometer EMC-30PC-UV (EMC Labs, Germany) was used to record the absorption spectra of the films. Elemental analysis was carried out on ED X-ray fluorescence spectrometer NEXDE (Rigaku, United States).
Results and discussion
Figure 2 presents electronic absorption spectra of [Co(bpy)(SCN)4]2+ in DMF. The absorption maxim is seen at 479 nm and the complex appears lilac. The spectrum considerably different form the spectrum of aqua complex of Co2+ where the absorption maximum is located around 550 nm. As cobalt(ll) has ^configuration, the expected num-
ber of absorption bands should be three. Although both d-d transitions are forbidden in centrosym-metric complexes (e.g. [Co(H2O)6]2+) because of the Laporte and the parity rules, such complexes possess low molar extinction coefficient meaning that less utilize the visual light (from the sun). Altering the molecular symmetry from centrosym-metric (molecule possessing center of inversion) to non-centrosymmetric leaves only the Laporte rule effective (Fig. 4). Moreover, planar and linear ligands as bpy and SCN respectivelylaeds to form more rigid molecule and may cause to the violation of spin-forbidden rules.
600
Wavelength (nm)
600
Wavelength (nm)
Figure 2. Absorption spectrum of [Co(bpy)(SCN)4]2+ in DMF
Figure 3 shows the absorption spectrum of [Co(bpy)(SCN)4]2+ in TEOS based sol-gel matrix. It can be seen the intense band at 479 nm blue-shifts by 14 nm upon the complex immobilization. This behavior was also observed elsewhere for Ru complexes in sol-gel matrix. Changing the molecular environment from less viscous media to the phase where free rotation is limited also initiate not only the chromic shifts in absorption spectra, but also in emission spectra. Hereof, we concluded that transferring the complex from the solution to the rigid membrane pores substantially improves molar absorptivity.
Figure 3. Absorption spectrum of [Co(bpy)(SCN)4]2+ in the sol-gel matrix
OH2
N III C I
S
H2O,,,,
Co
.............OH2
H2O"
"OH2
«2
■ S—c=
N
C
III
N
Figure 4. Centrosymmetric [Co(H2O)6]2+ and non-centrosymmetric [Co(bpy)(SCN)4]2+ molecules
400
500
700
800
400
500
700
800
C
Results of EDXRF analysis is shown in Fig. 5a initial and final composition of the immobilization
and 5 b. analysis shown that the dye doped matrix process. Experiments on leaching the dye from the
is consisted 99.8% (mass) SiO2 and 0.156% (mass) matrix also shown satisfying results and they con-
Co. converting the elemental cobalt to [Co(bpy) firmed that the sol-gel matrix is an excellent choice
(SCN)4]2+ gave a good consistency between the for further application.
b)
Figure 5. a) EDXRF spectrum of low Z-region; b) mid Z-region of the Co(bpy)(SCN)4]2+ in TEOS based sol-gel matrix
Conclusions Spectral evaluation of complex both in DMF and
[Co(bpy)(SCN)4]2+ complex has been syn- solid sol-gel matrix was discussed. Studies shown
thesized and its photochemical properties were that the sol-gel matrix is suitable environment for
studied. The synthesized complex was entrapped the complex and the dopant retains its photochemi-
in silicate xerogels produced by the sol-gel route. cal properties.
References:
1. Oregan B. and Gratzel M. A low-cost, high-efficiency solar-cell based on dye-sensitized colloidal TiO2 films. Nature - 353. 1991.- P. 737-740.
2. Vorontsov I. I., et al. Capturing and analyzing the excited-state structure of a Cu(I) phenanthroline complex by time-resolved diffraction and theoretical calculations. Journal of the American Chemical Society - 131(18). 2009.- P. 6566-6573.
3. Iwamura M., et al. Coherent nuclear dynamics in ultrafast photoinduced structural change of bis(diimine) copper(I) complex. Journal of the American Chemical Society,- 133(20). 2011.- P. 7728-7736.
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