Chen Tianfeng, Yang Fang, Zheng Wenjie, Bai Yan, Li Yiqun
(Dept. of Chemistry, Jinan University, Guangzhou 510632, China)
AbstractFour complexes were synthesized using triphenyl methane dyestuffs RhodamineB (RhB), Malachite Green (MG), Methyl Violet(MV), CrystalViolet(CV) as ligands at room temperature. The optimal medium for the reaction is 0.60~1.00mol/L phosphoric acid solution. All the complexes can be easily separated by the mixture of benzene and ether (VC/VC10O = 2/1). The complexes were characterized by ICP, EA, IR, UV-Vis, XRD and FS. The results indicated that the molecular formula for the complexes was (HL)(TeI). The coordinating mechanism and the spectral properties are also discussed.
Tellurium is a rare element, which is badly lacking and widely dispersive in lithosphere. It has been discovered that many telluriferous compounds have the anti- lipid peroxidation activity in biological and chemical systems and anticarcinoma activity . Trace amount of Te plays key role in nutrition and physiological health , and stimulative effect on the growth of Spirulina . Moreover, our research group has obtained protein and aminophenol containing Te resulting from the bio-organization of Te in yeast . It has not yet been confirmed whether Te is a necessary trace element in human’s body like Se, but it can be anticipated that Te will have wide applications in the field of life sciences. Therefore, it is necessary to find the protocol for determination of Te with high sensitivity and selectivity.
Triphenyl methane Dyestuffs have outstanding chromophorous characteristics, so they were broadly applied in analytical chemistry. They have vigorous potential in development [5-8] , but researches about coordinating mechanisms and properties of the ternary complexes with Te have not yet been reported. Therefore, it is very significant to synthesize and characterize these complexes with the purpose of finding new means of analysis.
1.1 Materials and instruments
TeO, RhB, MG, MV, CV, KI, Concentrated HCl (36%, HPO (7mol/L) were commercial analytical grade without further purification. The water was distilled before used.
The Te contents were analysed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) method on Optime 2000 DV spectrometer. The C, H, N were determinated by Vario EL spectrometer. IR spectra were obtained on a Equinox55 spectrometer in KBr pellet. UV-Vis spectra was recorded on a UV500 spectrophotometer in ethanol solution. X-ray diffraction patterns were recorded on a XD98 diffractometer equipped with Cu-anode, Radiation of Cu Ka (0.15405981nm), Power setting of 40KV, 20mA, Scan speed of 5s/step, Divergence slits of 1 deg., Receiving slits of 0.15mm, Soller slits of 1. Fluorescence spectra was recorded on a 970CRT fluorescent spectrophotometer (Shanghai SANCO Instrument Co.Ltd) in ethanol solution at concentrations listed in Table 5 at room temperature.
1.2 Samples preparation
The complexes (HL)(TeI) (L=RhB, MG, MV, CV) were synthesized by modified methods in literature [3, 4] . TeO 0.1g (0.00063 mol) was added to the concentrated HCl (2.0mL) and heated in the thermostatic water-bath until the complete dissolution of TeO2. After that, HPO (7 mol/L, ca. 20mL) was added. Then the water solution of triphenyl methane dyestuffs L (0.0052mol) and KI (4.0g, 0.024 mol ) was respectively added under vigorous stirring. The precipitate was filtered off after stirring for 10 min. at room temperature and washed thoroughly with water and then re-dissolved in the mixed solvent of benzene and ether and washed with 1M HCl solution. The resulting product was obtained as powdered materials after remove the organic solvent completely at ambient temperature.
2. RESULTS AND DISCUSSION
2.1 Results analysis
Elemental analysis results of the complexes are given in Table 1, the assignments of IR peak for ligands and complexes are given in Table 2, the data of UV-Vis spectra for ligands and complexes are given in Table 3, X-ray diffraction patterns and crystal degree are summarized in Fig.1 and Table 4, data of FS spectra for RhB and MG and their complexes are given in Table 5.
Table 1Results of elemental analysis (calculated value in parentheses) (%)
|(RhB)(TeI||4.06 (4.37)||46.19 (46.07)||4.37 (4.25)||3.95 (3.83)|
|(MG)(TeI||5.12 (5.16)||44.54 (44.91)||3.93 (4.06)||4.72 (4.55)|
The ligands in the complexes were calculated with the format of univalent cation (HL), eliding the proton just for the succinctness.
It is indicated in Table 1 that the molecular formulas of the complexes are (HL)(TeI). The ligands L coordinate with the center ion Te(IV) with the format of univalent cation (HL).Because of the existence of superfluous ligands in the system, some of them are wrapped in the precipitate, so the final product (ternary complexes) are difficult to be extracted completely and the results of the element analysis have a little warp compared with calculated value.
Table 2Assignment of IR spectra for ligands and complexes (cm-1
|as(COO-)||s(COO-)||vibration of framework
of aromatic ring
As seen in Table 2, four ternary complexes have similar Infrared (IR) spectra, which indicates that the complexes have similar structures. There are obvious differences in IR spectra between the complexes and the ligands, most of the characteristic bands have red shift or blue shift to a certain degree, and some of them disappear and new bands appear after the coordination.
n the case of (RhB)(TeI), a new stretching band appears at 427 cm-1. It is observed a shift of the stretching frequency of the carbonyl groups from 1703 cm-1, 1642 cm-1 and 1343 cm-1 for the free ligands to 1714 cm-1, 1644 cm-1 and 1345 cm-1 for the complexes. The difference of energy betweenas(COO-) and(COO-) is 299 cm-1. The peaks at 1703 cm-1 and 1714 cm-1 are attributed to the typical vibration of lactones carbonyl, which indicate that RhB existing interchangeably between lactone form and intra-salt form in the ligand and complex .
In the complexes of (HL)(TeI) (L= MG, MV, CV), new stretching bands appear at 422 cm-1 and 425 cm-1. A red shift of(-N-H) or(-O-H) is observed from 3442 cm-1, 3411 cm-1 and 3429 cm-1 for the free ligands to 3451 cm-1, 3443 cm-1 and 3448 cm-1 for the complexes. The bands arising from the stretching vibration of framework of aromatic ring appear wider, which suggests that the symmetry of the electron cloud in the ligands L is enhanced because of the introduction of Te(IV).
In the IR spectra of the ligangds and complexes, new peaks are observed in the low energy region of 427 cm-1, 425 cm-1 and 422 cm-1, it is believed that these peaks may be assigned to(Te-O) or(Te-N) mode. Simultaneously, the red shift of(-O-H) and(-N-H) may be occurred because of the reciprocity force between [ TeI8]4- and(Te-N), which make the dimensional resistance of these groups largened, therefore the stretching vibrations of -O-H and -N-H groups become more difficult.
As seen in Table.3, All ligands and complexes exhibitp-p transition in their UV-Vis spectra in ethanol. Strong absorptions are also observed in visible(vis) region. Four complexes have similar basic absorptions, but changes are also observed in the spectra.
Table 3Data of UV-Vis spectra for ligands and complexes
In the case of (RhB)(TeI), it is observed a change ofp-p transition from 226 nm, 258 nm and 282 nm occurring at the free ligand of RhB to 221 nm, 258 nm and 285 nm for the complexes, while the wavelength at maximum absorbance (max) in the ultraviolet region shifts from 258 nm to 221nm. In addition, absorption band occurring at 305nm in RhB disappears in the complexes and absorption band at 355nm due to n-p transition has a hypsochromic shift. It is also observed that absorption band at 547nm has a bathochromic shift of 7nm while its intensity weakened.
Ligands and complexes for MG, MV and CV have similar UV-Vis spectra since all of them belong to triphenyl methane dyestuff having similar molecular structure. New absorptions occurring at 428nm, 353nm and 356nm are observed in the spectra of complexes attributed to electric charge transition from the ligands to the center ion Te(IV). In the complex of (MG)(TeI), new absorption bonds occur at 257nm and 317nm, which are respectively due top-p transition and n-p transition. Shift of other absorption bonds is also observed from 223 nm, 366 nm and 620nm to 209nm, 360nm and 626nm.The spectra of the complexes of (MV)(TeI) and (CV)(TeI) have comparability, the relative intensity of absorption at 249nm and 248nm due top-p transition become weakened.
(a) RhB system (b) MG system
(c) MV system (d) CV system
Fig. 1 XRD patterns of ligands and complexes (1 TeO; 2 ligands; 3 complexes)
The patterns of X-ray diffraction of ligands and complexes are shown in Figure.1, indicating that: (1) X-ray diffraction of the complexes is different from the relative ligands obviously; (2) the complexes are not simple lap joint of the ligands L and TeO; (3) the chief diffractions of the reactants disappear in the patterns of complexes, indicating new compound formed.
In the XRD patterns in Figure.1, the crystal diffraction and the non-crystal diffraction are identified by using the multiple separation method in computer, then calculate the crystal degree of ligands and complexes, the results are given in Table 4.
Table.4Crystal degree of ligands and complexes
As seen in Table. 4, the crystal degree of RhB and MG descend obviously after coordinating with Te(Ⅳ) and forming the ternary complexes, while that of MV and CV heighten a little on the contrary.
Table 5Data of Fluorescent spectra of the ligands and complexes
|ex / nm||em / nm||em|
Determination condition.Scan speed:high speed, sensitivity 1, Ex slit width 10, Em slit width 10.
As seen in Table.5, RhB has strong fluorescence, when it coordinates with Te(IV) forming the ternary complex (RhB)(TeI), the wavelength of excitation (ex) has a hypsochromic shift of 1.3nm while wavelength of emission of 8.6nm and the intensity of luminescence enhance about 2 times. As far as MG and its complex (MG)(TeI) are concerned, there is no fluorescence observed with the sensitivity of 1, while faint fluorescence can be observed when the sensitivity heighten to 3, but no fluorescence is observed in both condition from MV, CV and their complexes.
Ligands RhB, MG, MV and CV are similar in molecular structure, but different in fluorescence properties, which is attributed to conjugate system magnitude, share-plane configuration of conjugate π-bond and its rigidity and so on. There is a oxygen bridge in RhB which links three aromatic ring into a big conjugate system and fixups the adjacent aromatic rings in the same plane enhancing the rigidity, so RhB has strong fluorescence,but there are three aromatic ring existing isolated in the molecule of MG, CV and MV, there is just faint even no fluorescence observed in the free ligands and their complexes.
Triphenyl methane dyestuffs exist as multi-form which keep equilibrium in aqueous solution system10] . Such as MG, it can exist as neutral molecule L in alkaline solutions and as univalent cation(HL) or bivalent cation (HL)2+ or trivalent cation (HL)3+ in acidic solutions, but the latter two forms can just exist in strong acidic condition because of their instability in solution system. Ligands RhB, MV and CV also have similar behaviors in aqueous solution system.
It is advantageous for the ligands exchange of TeO2- in the acidic environment:
TeO2- + 8I + 6H = TeI4- + 3H
The mixed aqueous solution of HTeO and KI is an instable system in thermodynamics, which can be indicated by the Eof the hereinafter reaction.
TeO2- + 6I + 6H = Te↓ + 2I + 3HO E=1.64V
The rapid forming of high-coordinate anion [ TeI] 4- weakens the polarization ability of Te(IV) to I to a certain extent and the joining of big volume organic cations (HL)+ can restrain the distortion ability of I, which has stabilization effect on [ TeI] 4-
It is believed that Te(IV) forms [ TeI] 4- first with I in phosphate solution (about 0.8 mol/L) containing KI, then the complexes whose molecular formulas are (HL)(TeI) are obtained according to the series complicated reactions of [ TeI] 4- and (HL). But they are not simple ions association compounds. In the IR spectra of the complexes, new peaks probably assigned to(Te-O) or(Te-N) mode are observed indicating the forming of Te-O and Te-N bands, which suggest that there are strong static reciprocity force, exchange and recompositin of ligands existing between [ TeI] 4- and (HL).The 8 I may not just centralize around Te, but having more suitable positions for getting better energy of static reciprocity force. Because of the complexity of the complexes systems, it will be further clarified in our later paper.
The luminescent properties of the complexes synthesized always arise people’s interest. In a general way, in water system, the forming of (RhB)(TeI) system will result in the fluorescence quenching of RhB, which was believed due to the forming of complex nanoparticle that can agglomerate into unshaped aggregation, enwrap many RhB molecules and restrain them from absorbing excitated photons. This characteristic of RhB has been widely applied in determination of trace or minim Te in analytical chemistry field[5, 8] . Our researches have confirmed the existing of this kind of nanoparticle in the system of RhB-I-Te(IV) which will be given detailed discription in our later paper. As seen in Table.5, fluorescence enhancement was observed obviously in (RhB)(TeI) compared to RhB, which may be attributed to the ethanol solvent, because the (RhB)(TeI) nanoparticle could be decomposed into individual (RhB)(TeI) association molecule by alcohol. Then the RhB molecules enwrapped were released and the fluorescence resumed simultaniously.