Spectra Analyses of Europium Complexes with Benzoic Acid and Its Derivatives
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In order to study regularity of fluorescence of complexes about rare earth with different benzoic acid,we have prepared much of BA-compiexes,RC_6H_4COOH(R=o-NH_2,H,p-NH_2,o-OH,m-Cl,o-COOH,m-COOH,p-COOH,p-OH,m-NO_2,3,5-Dinitro,p-Br,o-I,2-OH-5-SO_3H.They can be synthesized complexes with Sm~(3+),Eu~(3+),Tb~(3+),Gd~(3+).Under UV-excitation the complexes with Eu~(3+),Tb~(3+) have higher emitting(intensity) than complexes with Sm~(3+),Gd~(3+).There are some science bases about study a new luminophor.Spectra analyses of the complexes of europium with benzoic acid and its derivatives are discussed.The binary complexes of europium with benzoic acid and its derivatives(benzene carbonic acid,phthalic acid,isophthahc acid,salicylic acid,o-aminobenzoic acid sulfosalicylic acid) have been synthesized.They were characterized by(elemental) analysis,UV-Vis,IR,H NMR,fluorescence spectra and molar conductance.The UV spectra showed that the complexes' ultraviolet absorption were from the ligands(220~350 nm),so that it could transfer energy to rare earth.The measurement results of the emission spectra of the complexes indicated as follows the emission of Eu(BA)_3,Eu(m-Phth)_3·3H_2O and Eu(o-Phth)_3·3H_2O consisted of three peaks at 582,596,and 618 nm which were caused from ~5D_0→~7F_J(J=0,1,2) transition of Eu~(3+) respectively.Among these peaks the emission from ~5D_0→~7F_2 is the shrongest.But the emission of Eu o-aminobenzoic acid consisted(of three) peaks at 399,452,547 nm,and that of sulfosalicylic acid-Eu only one peak at 407 nm,which(were caused) from ligands.Fluorescence spectra show that there aren't red-characteristic emission of Eu in (Eu(o-Amino))_3 and Eu(Ssal)_3.Keywords:
Benzoic acid
Europium
Phthalic acid
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Rare earth complexes have become excellent luminescence materials,this is related to lanthanide(ions') peculiar characteristics,and have potential use in laser,photoluminescence and electroluminescence.Rare earth complexes with aromatic carboxylic acids are a kind of luminescent materials with good properties. So much attention was paid to the fluorescence properties of these complexes.There are some reports about fluorescence properties of the complexes of a part of rare earth with phthalic acid and terbium with benzoic acid and salicylic acid.However,no report on systemic study of the fluorescence properties concerning rare earth complexes with different aromatic carboxylic acids has been reported.For this purpose,we have synthesized fourteen complexes of Sm,Eu,Tb,Dy with benzoic acid derivatives: RC_6H_4COOH(R=o-NH_2,H,p-NH_2,(o-OH),m-Cl,o-COOH,m-COOH,p-COOH,p-OH,m-NO_2,3,5-Dinitro,p-Br,o-I,2-OH-5-SO_3H)and it is found that the complexes of Sm and Dy with these aromatic acids show little fluorescence,but Eu and Tb with some of these aromatic acids show strong fluorescence under the excitation of UV,and that the complexes of terbium with sulfosalicylic acid have the strongest fluorescence intensity.In the present paper,terbium complexes with aromatic acids were synthesized and their fluorescence properties were investigated.The synthetic process was as follows: The aqueous TbCl_3 solution was slowly added to ligand solution(according) to the molar ratio of Tb~(3+)∶ligand=1∶3 or 2∶3(phthalic acid,m-phthalic acid) at 80 ℃ under(stirring.) The pH of the mixture was adjusted to 6.0～6.5 by addition of sodium hydroxide solution.Thus,white precipitates of the complexes came into being.After another two hours,stop stirring,the mixture was cooled to room temperature.The white precipitates of the complexes were filtered,washed with deionized(water) and ethanol till no chloridion could be found, then dried at 85 ℃ under vacuum for 4 h.The compositions of samples were identified by elemental analyses.UV,IR of the complexes also have been investigated.The UV spectra indicated that the complexes' ultraviolet absorption was mainly the ligands' absorption,but the location of peak drifted.The IR spectra showed that the IR spectra of complexes are dif-(ferent) from those of free ligands and the band at 400～500 cm~(-1),due to the stretching vibration of Tb-O,is absent for free ligands.The fluorescence properties were investigated by using luminescence spectroscopy,the results showed that all the six complexes of terbium exhibited excellent luminescence,due to the transition from the lowest excited state ~5D_4 to ~7F_J ground state manifold,and the complexes of terbium with sulfosalicylic acid had the strongest fluorescence intensity.
Terbium
Phthalic acid
Benzoic acid
Europium
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Two binary complexes of Eu3+ and Tb3+ with 2-thiophene carboxylic acid and two ternary complexes of Eu3+ and Tb3+ with 2-thiophene carboxylic acid(L)-2, 2'-bipyridine were synthesized. By elemental analysis, rare earth coordination titration, and molar conductivities studies, the compositions of the complexes were suggested as REL3 x 2H2O and REL3L' x C2H5OH(RE=Eu, Tb, L = 2-thiophene carboxylic acid, L' = 2, 2'-bipyridine) respectively. The ligands and coordination compounds were studied by means of IR spectra, 1H NMR and fluorescence excitation and emission spectra. IR spectra and 1H NMR studies indicate that 2-thiophene carboxylic acid was bonded with RE(III) through oxygen atoms in the carboxyl group, and 2, 2'-bipyridine ligand was bonded to RE(III) through nitrogen atoms. The fluoresence spectra showed that the fluorescence emission intensity of ternary complexes was stronger than that of the binary complexes.
2,2'-Bipyridine
Proton NMR
Bipyridine
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Characterization
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The studies on the luminescence property of complexes of rare earth benzoate are attracting people's more interest increasingly.The luminescence of both complexes of Eu-Tb benzoate and complexes of Eu-La benzoate have been reported already;a high efficient Tb-Gd benzoate luminescence material was obtained by replacing a part of Tb~(3+) with Gd~(3+);also fluorescence intensity can be enhanced by replacing a proportion of Eu~(3+) with La~(3+).But interrelated report about Ca~(2+) and Ba~(2+) alkaline earth ions effecting fluorescence intensity of Eu~(3+) was not seen yet.So group members decided to complete this work by choosing facile alkaline earth metal and it has significant value if corking effect was gotten.Aim at this,a series of complexes of benzoic acid with europium-calcium and europium-barium were synthesized by the reaction of europium chloride and calcium chloride(or barium chloride) with sodium benzoate in aqueous solution.Their composition is expressed with the general formula(Eu_(1-x)Ca_x)L_(3-x) and(Eu_(1-x)Ba_x)L_(3-x),where L=C_6H_5COO~-,x=0~1.0).Their infrared and fluorescence spectra were investigated.The characteristic asymmetric(ν_(as)) vibrations of carboxyl group for EuL_3,(Eu_(1-x)Ca_x)L_(3-x) and(Eu_(1-x)Ba_x)L_(3-x)(x0.7) shift to lower frequency and the other complexes shift to higher frequency;in comparison with symmetric(ν_s) shift to lower frequency for EuL_3 and the other complexes shift to higher frequency.What is more,both the absorption bands(ν_(as) and ν_s) show splitting.From above analysis,we could draw a conclusion that the coordinating pattern of the carboxyl groups in the complexes is the form of chelating-bidentate and the tridentate chelating-bridging.The dependence of the relative fluorescence intensity of the complexes upon the content for Ca~(2+) ion and Ba~(2+) ion was discussed.The results showed that the emission intensity for Eu~(3+) ions can be greatly enhanced if a part of Eu~(3+) ion in europium benzoate was substituted by Ca~(2+) ion or Ba~(2+) ion.When x=0.1,the fluorescence intensity of the complexes is the highest.So it can be saying that not only the reserves abundant and inexpensive alkaline earth metallic ions were adulterated into complexes but higher fluorescence intensity than pure europium-benzoate complexes was achieved.These research results are very successful and will have wider application foreground.
Europium
Barium
Benzoic acid
Sodium benzoate
Alkaline earth metal
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It is well known that aromatic acids serve as excellent ligands to effect sensitization of lanthanide fluorescence. 1,3,5- H_3BTC has three carboxylate groups and displays widely varying coordination manner, functioning as a monodentate, bidentate, bridging or chelating ligand in complexes with metal ions. On the other hand, the rare earth carboxylate complexes are the active area of research due to their fluorescence and application in high-teach industry, the application foreground is very fast. In recent years, there are many studies carrying on the carboxylate complexes in order to look for the good fluorescent materials, one of the major activities in these studies is the enhancement of fluorescence by using of certain rare earth ions,such as La 3+,Y 3+and Gd 3+. The published dates on these were mainly focused on benzoic acid and benzene dicar- boxylate acid complexes, the complexes of trimesic acid with europium and lanthanum were comparatively scare. Only europium-trimesic acid fluorescence complexes were studied.A series of mixed rare earth complexes La_xEu_ 1-x (BTC) ·nH_2O ( H_3BTC = 1, 3, 5-H_3BTC, x= 0, 0.1, 0.3, 0.5, 0.7, 0.9) have been synthesized by the reaction of trivalent rare earth chlorides with trimesic acid. The contents of rare earth, C and H were measured by using EDTA titration method and a Vario EL elemental analyzer, the constitution of these complexes was confirmed respectively as follows: La_xEu_ 1-x(BTC)·nH_2O (x= 0, 0.1, 0.3, 0.5, 0.7, 0.9, n=0, 0.5,1.0).The IR spectra of free ligand and complexes were recorded by FTZR-8900 infrared spectroscopy with KBr pellet in the range of 350~3 500 cm -1. There is obviously difference between the ligand and complexes. The results show that the similar structures of the complexes and the different coordination functions of the carboxylate groups. Fluorescence spectra were carrying out by using a Hitachi F-4500 fluorescence spectrophotometer. The results indicate that the complex can emit intense characteristic fluorescence from europium ion, the emission peak centered at 578~582 nm (5D_0→7F_0),585~600 nm(5D_0→7F_1),605~630 nm(5D_0→7F_2),645~660 nm(5D_0→7F_3),685~700 nm (5D_0→7F_4), the intensity of the fluorescence of the series complexes were greater in 5D_0→7F_1 and 5D_0→7F_2, and both the positions show splitting emission peaks. These results show that the coordinating pattern of the carboxylate groups were different. In addition, the fluorescence intensities of europium ions were sensitized by the doping elements lanthanum ions, and the intensity of fluorescence is the best when La 3+∶Eu 3+=0.3∶0.7, but the position of the emission peak does not changed. In conclusion, a series of mixed rare earth complexes La_xEu_ 1-x (BTC)·nH_2O (x= 0, 0.1, 0.3, 0.5, 0.7, 0.9) have been synthesized by hydrothermal treatment. They can emit strong fluorescence.
Trimesic acid
Europium
Carboxylate
Benzoic acid
Lanthanum
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Three novel europium complexes,Eu(Hhqc)3(H2O),Eu(Hhqc)3Phen(H2O)5 and Eu(Hhqc)3TPPO(H2O)5 were synthesized using 2-Hydroxyquinoline-4-carboxylic acid(H2hqc),1,10-phenanthroline(Phen)and triphenyl phosphine oxide(TPPO)as the ligands.The complexes were characterized by elemental analysis and infrared spectrum.The IR spectra indicated that the complex Eu(Hhqc)3Phen(H2O)5 has a largerΔνthan that of NaHhqc,and carboxylate ions in the phenylglyoxyate are coordinated as monodentate ligands.TheΔνvalues of the Eu(Hhqc)3(H2O)and Eu(Hhqc)3TPPO-(H2O)5 are smaller than that of NaHhqc,the carboxylate ions coordinate to Eu3+ with bidentate chelating mode.The fluorescence properties of the complexes were studied at room temperature.Each complex shows five emission bands at 581,594,615,654 and 703nm,which are assigned to the characteristic emission 5D0→7FJ(J=0,1,2,3,4)transitions of Eu3+,respectively.The fluorescence intensity becomes stronger after the additions of Phen and TPPO,and Phen is better.
Europium
Carboxylate
Phosphine oxide
8-Hydroxyquinoline
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Rare earth binary complex Eu(BA)-3,ternary complex Eu(BA)-3·phen and(Eu-Y)BA-3·phen were synthesized.Many advanced approaches,such as element analysis and FTIR spectra,were used to determine their composition and structures.In addition,their fluorescent properties were studied by fluorescent spectra and lifetime.The results show that the fluorescence is the strongest and the lifetime is the longest when the mole ratio of europium to yttrium is 3∶7.The results of fluorescent intensity were also fitted by mathematical tools.It shows that the degree of Y~(3+) enhance Eu~(3+) fluorescence decreases by exponential decay mode when the content of Y~(3+) decreases.
Europium
Phenanthroline
Rare-earth element
Benzoic acid
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A series of dinuclear complexes of salicylic acid and o-phenanthroline with different molar ratios of Eu~(3+) to Y~(3+) have been synthesized.Their composition was Eu_xY_(1-x)(sal)_3(phen)(x=0.1~1.0).Their UV spectra,IR spectra and fluorescence spectra were studied.The UV absorption of the complexes comes mainly from that of ligands.The fluorescence spectra of the complexes indicate that the fluorescence emision intensity of europium ion was sensitized by yttrium ion in the complexes.These facts show that not only the ligands but also the yttrium complex can transfer the absorbed energy to Eu~(3+) ion in the complexes.
Europium
Phenanthroline
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Three coordination compounds of perchlorate rare earth(Nd~(3+),Eu~(3+),Tb~(3+)) with o-aminobenzoic acid have been synthesized by solid state reaction. The elemental analysis,molar conductivity and DTA-TG studies suggested that the complexes have the composition of ·6H_2O(RE=Nd,Eu,Tb; LH: C_6H_4(NH_2)COOH;L~-:C_6H_4(NH_2)COO~-) .IR studies indicated that the ligand L~- is bonded with RE(III) ions though two oxygen atom in carboxy group,Amino group are not coordinated .The molar conductivities indicated that ClO_4~- are coordinated with RE~(3+), coordination compounds are non-electrolyte. In the solubility experiment it was found that the complexes have hight solubility in ethanol.In the fluorescent spectra of ·6H_2O ,it was found that Tb~(3+)has a strongly luminescent property.
Molar conductivity
Perchlorate
Aminobenzoic acid
Coordination sphere
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