Various synthetic schemes were explored in order to develop a general synthesis of γ-diketones. The addition of organometallic reagents to several γ-dicarboxylic acids and γ-dinitrile compounds failed to produce any ketonic product, whereas addition to γ-diesters and γ-diacid chlorides gave only small amounts of the diketones in a mixture of products. A series of γ-diketones was prepared in low to moderate yields by way of the corresponding acetylenic glycols. These glycols were made by treating acetylenedimagnesium bromide with various aldehydes and then hydrogenation to the saturated γ-dialcohols. Oxidation of the alcohols produced diketones of type RCOCH_2CH_2COR where R = ethyl, isopropyl, t-butyl, n-propyl, n-hexyl, phenyl and cyclohexyl radicals. Good yields of γ-diketones were obtained by dialkylating 2,2'-ethylenebis(m-dithiane) followed by hydrolysis. Except for isopropyl iodide, the alkylation was successful only with primary alkyl halides. Diketones of the above type where R = ethyl, isopropyl, n-propyl, isobutyl, n-butyl, isoamyl, and benzyl radicals were prepared.

Four γ-diketones were synthesized by using a modification of the Kolbe electrolytic condensation of β-ketocarboxylic acids. [--see equation in thesis--] The following γ-diketones were synthesized in moderate yields: 2,5-hexanedione, 4,7-decanedione, 2,2,7,7-tetramethyl- 3,6-octanedione, and 1,4-diphenyl-1,4-butanedione (34, 39, 23, and 27, respectively). However, attempted preparation of the following γ-diketones failed: 3,4-dimethyl- 2,5-hexanedione, 3,3,4,4-tetramethyl-2,5-hexanedione, and 1,4-di(2-thienyl)-1,4-butanedione. Attempts to electrolytically condense α-alkyl and α, α-dialkyl substituted monocarboxylic acids have been reported and all attempts have ended in failure; similarly, the attempts to synthesize 3,4-dimethyl and 3,3,4,4-tetramethyl- 2,5-hexanedione from 2-methyl and 2,2-dimethyl-3- oxobutanoic acid, respectively, failed. The preparation of 1,4-di(2-thienyl)-l,4-butanedione failed because the product or side product was not soluble in the solvents tried and this resulted in precipitation of a non-conducting white product film on the electrodes, thus, preventing further electrolysis.

The vinylepoxide-diliydrofuran rearrangement offers a route to substituted 2,3- dihydrofurans with a high degree of diastereoselectivity. The rearrangement proceeds via an ylide-type intermediate arising from the thermolysis of a carbon-carbon epoxide bond. This thesis discusses work aimed at developing the rearrangement, introducing asymmetric control, and application of the dihydrofuran products in target molecule synthesis. Synthesis of the vinylepoxide rearrangement precursors is described, and development of the rearrangement to achieve a moderate scale rearrangement process is discussed. Alternative rearrangement technologies are also explored. Asymmetric induction into the rearrangement was approached by the use of chiral auxiliaries and in particular C2 symmetric amines. A novel synthesis of (S,S)-2,5-diphenylpyrrolidine and (S,S)-2,6-diphenylpiperidine is reported. High degrees of enantiomeric purity were achieved through the application of an effective oxazaborolidine catalyst in the reduction of dibenzoylethane and dibenzoylpropane. Use of this chiral reduction catalyst on further diketones is described. Application of the dihydrofuran products in the synthesis of several 2,6-disubstituted- 3,7-dioxabicyclo[3.3.0]octanes. These compounds, commonly termed furofuran lignans exhibit a wide range of biological properties. The dihydrofuran products were combined with a range of dimethylacetals, in a one pot synthesis, with high degrees of stereocontrol, by a Noyori type transacetalisation. Further derivatisation of these bicyclic compounds was accomplished and is discussed.Finally, with the vinylepoxide - dihydrofuran rearrangement established a preliminary exploration of the related vinylaziridine - 2-pyrroline rearrangement is reported.

No description available.

The thesis titled “Novel Strategies for the Synthesis of Organo-Sulfur Compounds Under Metal-free Reaction conditions” is presented into three main sections. Section A– deals with the synthesis of thiourea and thioamide. Section B– describes the sulfenylation of electron-rich arenes, ketones and β- diketones Section C– deals with the sulfur/fluorine assisted deacylation of α-sulfenylated β- diketones. Section A: This section is divided in to two chapters, Chapter 1 and Chapter 2. Chapter 1 of this section describes the non-isothiocyanate route to obtain trisubstituted thioureas of arylamines by using in situ generated dithiocarbamates of secondary amines. Trisubstituted thioureas of aryl amines are important precursors for the synthesis of heterocyles like 2-aminobenzothiazoles derivatives,1 amidines,2 and guanidines.3 Therefore, this strategy provides an excellent opportunity to access thioureas containing primary aryl amines without employing isothiocyanates. From the current method, the broad substrate scope was achieved with excellent yield of the corresponding products. Further, under the optimized reaction conditions a variety of functional groups like ketones, carboxylic acids, amides and sulfonamides were found to be well tolerated. A few representative examples are shown in Scheme 1.4 (a) Jordan, A. D.; Luo, C.; and Reitz, A. B. J. Org. Chem. 2003, 68, 8693. (b) Joyce, L. L.; Batey, R. A. Org. Lett. 2009, 11, 2792 and references therein. (c) Jamir, L.; Khatun, N.; Patel, B. K. RSC Adv., 2011, 1, 447. 1 Biswas, K.; Greaney, M. F. Org. Lett. 2011, 13, 4946. 2 (a) Wilson, L. J.; Klopfenstein, S. R.; Li, M. Tetrahedron Lett. 1999, 40, 3999. (b) Schneider, S. E.; Bishop, P. A.; Salazar, M. A.; Bishop, O. A.; Anslyn, E. V. Tetrahedron 1998, 54, 15063. 3 Varun, B. V.; Prabhu, K. R. RSC Adv.2013, 3, 3079. Synopsis Chapter 2 describes the rapid, high yielding and easily isolable method for the synthesis of thioamide by nucleophilic addition of electron-rich arenes to isothiocyanates. Thioamides are essential structural motifs which are found in a variety of biologically active molecules.5 They are also crucial building blocks for synthesizing sulfur conntaining heterocycles.6 The current method employs triflic acid (TfOH) to activate the nitrogen of isothiocyanate, where as, in the earlier methods AlCl3 was used.7 Also, the reaction was found to be highly regioselective and the broad substrate scope of the reaction was demonstrated (Scheme 2).85 (a) Cremlyn, R. J. An Introduction to Organosulfur Chemistry,John Wiley and Sons, Chichester, 1996. (b) Gottesman, M. M.; Fojo, T.; Bates, S. E. Nat. Rev. Cancer 2002, 2, 48; (c) Angehrn, P.; Goetschi, E.; Gmuender, H.; Hebeisen, P.; Hennig, M.; Kuhn, B.; Luebbers, T.; Reindl, P.; Ricklin, F.; Schmitt-Hoffmann, A. J. Med. Chem.2011, 54, 2207 6 (a)Shibuya, I.; Honda, K.; Gama, Y.; Shimizu, M. Heterocycles 2000, 53, 929. (b) Takido, T.; Itabashi, K.; Synthesis 1985, 430. (c) Shibuya, I.; Gama, Y.; Shimizu, M. Heterocycles 2001, 55, 381. (d) Wang, H.; Wang, L.; Shang, J.; Li, X.; Wang, H.; Gui, J.; Lei, A. Chem. Commun., 2012, 48, 76. (e) Alla, S. K.; Sadhu, P.; Punniyamurthy, T. J. Org. Chem., 2014, 79, 7502. (f) Chaudhari, P. S.; Pathare, S. P.; Akamanchi, K. G. J. Org. Chem., 2012, 77, 3716. (g) Mendoza-Espinosa, D.; Ung, G.; Donnadieu, B.; Bertrand, G. Chem. Commun.,2011, 47, 10614. (h) Potts, K. T.; Houghton, E.; Singh, U. P. J. Org. Chem., 1974, 39, 3627. 7 a) Jagodzinski, T.; Jagodzinska, E.; Jabłonski, Z. Tetrahedron 1986, (b) Jagodzinski, T. Synthesis 1988, 717. 8 Varun, B. V.; Sood, A.; Prabhu, K. R. RSC Adv.2014, 4, 60798. Scheme 2: Synthesis of thioamide Section B This section is divided in to two chapters, Chapter 1 and Chapter 2. Chapter 1 of this section describes a facile transition metal-free oxidative CDC (Cross Dehydrogenative Coupling) reaction leading to a regioselective thiolation of electron-rich arenes and hetero-arenes. This strategy provides a rare opportunity of using thione in a CDC reaction to form C–S bonds to obtain arylthiobenzoxazoles, hetero-arylthiobenzoxazoles and arylthiobenzthiazoles, which are pharmaceutically valuable compounds.9 This highly regioselective CDC reaction is unique as it requires the reversing the reactivity of sulfur to form the C–S bonds. Despite the propensity of thiols to undergo oxidation, this method provides an elegant and new avenue for synthesizing thioethers of benzazoles (Scheme 3).10 a) Greco, M. N.; Hageman, W. E.; Powell, E. T.; Tighe, J. J.; Persico, F. J. J. Med. Chem. 1992, 35, 3180. b) Zhang, J.-T.; Qi, J.; Feng, H.; Dong, Z. WO2010048603, 2010. c) Greco, M. N.; Hageman, W. E.; Powell, E. T.; Tighe, J. J.; Persico, F. J. J. Med. Chem. 1992, 35, 3180. d) Barchuk, W. T.; Dunford, P. J.; Edwards, J. P.; Fourie, A. M.; Karlsson, L.; Quan, J. M. US 2008194630. e) Koci, J.; Klimesova, V.; Waisser, K.; Kaustova, J.; Dahse, H.-M.; Moellmann, U.;Bioorg. Med. Chem. Lett. 2002, 12, 3275. 10 Varun, B. V.; Prabhu, K. R. J. Org. Chem.2014, 79, 9655. xii Synopsis Scheme 3: C-H-Functionalization of electron-rich arenes Chapter 2 is discussed in two parts, Part A and Part B. Part A: deals with the C–H functionalization of β-diketones via CDC reactions. A variety β-diketones were sulfenylated at α-position with a variety of benzazole-2-thione derivatives. Sulfenylation of β-diketones is challenging as β-diketones undergo deacylation after sulfenylation in the reaction medium.11 The highlight of this work is that the resultant products do not undergo deacylation. Under the optimal reaction conditions a variety of functional group like ketones, acids and esters were well tolerated. Also, the resultant sulfenylated β-diketones were further manipulated to α,α-disubstituted β-diketones and pyrazoles (Scheme 4).12 11 (a) Ogura, K.; Sanada, K.; Takahashi, K.; Iida, H. Tetrahedron Lett.1982, 23, 4035. (b) Zou, L.-H.; Priebbenow, D. L.; Wang, L.; Mottweiler, J.; Bolm, C. Adv. Synth. & Catal. 2013, 355, 2558. 12 Varun, B. V.; Gadde, K.; Prabhu, K. R. Org. Lett. 2015, 17, 2944. Scheme 4: C-H Functionalization of β-diketones via CDC reaction Chapter 2, Part B: deals with the C–H functionalization of ketones via CDC, which is the continuation of the above discussed work (Chapter 2, Part B). The products obtained from this method can be further modified and can be used for the synthesis of α,β-unsaturated carbonyl compounds under Trost or Julia olefination reaction conditions.13 A variety of actophenone derivatives, propiophenone derivatives and simple alkyl ketones were sulfenylated at the α-position with various benzazole-2-thiones (Scheme 5).14 Scheme 5: C-H Functionalization of ketones via CDC reaction (a) Trost, B. M.; Salzmann, T. N.; Hiroi, K. J. Am. Chem. Soc. 1975, 98, 4887. (b) Baudin, J. B.; Hareau, G.; Julia, S. A. Tetrahedron Lett. 1991, 32, 1175. (c) Blakemore, P. R.; Cole, W. J.; Kocienski, P. J.; Morley, A. Synlett 1998, 26. 14 Manuscript under preparation. Section C This section describes the ‘sulfur/fluorine assisted deacylation of β-diketones.’ Achieving a controlled mono fluorination at α- position of a ketone group is a difficult task. Therefore, an alternate approach is to have a sulfide group at α-position to a ketone (electron withdrawing moiety) and thereby providing additional stability to the generated reactive intermediate at α-position. Till date, this transformation has been achieved only by electrochemical methods.15 In continuation of our earlier work of α-sulfenyl β-diketones for exploring the synthetic utility of α-sulfenyl β-diketones (like benzylation and allylation), we performed the fluorination reaction. In this reaction, the fluorinated product (a diketone) underwent a de-acylation process to furnish the corresponding α-fluorinated ketone and we further optimized the reaction conditions and explored the substrate scope for this reaction. Under the optimized reaction conditions a variety of fluorinated products were isolated in excellent yield (Scheme 6) Scheme 6: Sulfur/Fluorine assisted deacylation of β-diketones 15Fuchigami, T.; Shimojo, M.; Konno, A.; Nakagawa, K. J. Org. Chem. 1990, 55, 6074 16 Manuscript under preparation.

This dissertation describes the investigation of the utility of metal–bis(oxazoline) complexes in catalytic asymmetric reactions. The development of Cu(II)-catalyzed regio- and enantioselective additions of silylketenthioacetals into diketones is discussed in the first chapter. \(Cu(OTf)_2(t-BuBox)\) complexes were found to be an effective catalyst with a broad substrate scope, providing tertiary alcohols in high yields, regioselectivities, and enantioselectivities. A model that accounts for the absolute stereochemistry of the product based on A1,3–interaction was proposed. Relative reactivities among diketones were also investigated. The second chapter reports the investigation of Diels–Alder reactions of N-allenoyloxazolidinones. The reaction between 3-buta-2,3-dienoyloxazolidin-2-one and cyclopentadiene was catalyzed by \(Cu(SbF_6)_2(H_2O)_2(t-BuBox)\) complexes, providing the cyclic product in high yield and enantioselectivity. The endo isomer was obtained as a major product with high selectivity. Relative reactivity between N-allenoyl oxazolidinones and unsaturated N-acyloxazolidinones was also studied. / Chemistry and Chemical Biology

Compounds containing the 2,3-dioxabicyclo[2.n.n] moiety, otherwise known as bicyclic endoperoxides, are a class of cyclic peroxides that are readily found in nature and can be utilized as important synthetic building blocks. The chemistry of endoperoxides has chiefly been concerned with the relative weakness of the peroxide bond, with comparatively little attention directed towards transformations of the alkene unit within these compounds. Therefore the focus of this thesis is on dihydroxylation of bicyclic endoperoxides and examination of their further utility. A broad range of 1,4-disubstituted-2,3-dioxabicyclo[2.2.2]oct-5-enes were synthesized featuring a variety of alkyl and aryl substituents. These compounds were subsequently dihydroxylated with osmium tetroxide to yield diols anti to the peroxide linkage, as single diastereomers, in excellent yields. Reduction of the peroxide bond afforded cyclohexane-1,2,3,4-tetraols of toxocarol relative stereochemistry in excellent yield; this configuration of hydroxyl groups is quite prevalent in nature. In order to demonstrate the synthetic scope of dihydroxylation of bicyclic endoperoxides followed by reduction of the peroxide linkage, tetraol formation from alkyl and aryl substituted diols was examined. It was confirmed that both alkyl and aryl substituents can be tolerated in the 1,4-positions. Dihydroxylation of endoperoxides containing H atoms at the 1,4-positions was also documented. The methodology of dihydroxylation followed by reduction of the peroxide linkage was employed to synthesize the reported natural product (1S,2R,3S,4R,5R)-2-methyl-5-(propan-2-yl)cyclohexane-1,2,3,4-tetrol in a short sequence from (R)-α-phellandrene. The 2,3-dioxabicyclo[2.2.2]octane-5,6-diols discussed above were also found to undergo an extremely clean rearrangement to yield 1,4-dicarbonyls and glycoaldehyde, a rearrangement not reported in the literature. The possible mechanism of this rearrangement was probed and is discussed in detail. The repercussions of diol orientation to product outcome were also investigated. Finally, the possibility of expanding the scope of synthetic application for this rearrangement, particularly the potential for synthesis of optically pure 1,4-dicarbonyls is discussed. Some preliminary results are reported. / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

No description available.

Made available in DSpace on 2014-12-17T15:01:24Z (GMT). No. of bitstreams: 1 ClaudioDM_DISSERT.pdf: 902689 bytes, checksum: 9281415acd8fbe6a15da6b807a1d9ff7 (MD5) Previous issue date: 2010-09-10 / Among the main challenges in the beer industrial production is the market supply at the lowest cost and high quality, in order to ensure the expectations of customers and. consumers The beer fermentation stage represents approximately 70% of the whole time necessary to its production, having a obligatoriness of strict process controls to avoid becoming bottleneck in beer production. This stage is responsible for the formation of a series of subproducts, which are responsible for the composition of aroma/bouquet existing in beer and some of these subproducts, if produced in larger quantities, they will confer unpleasant taste and odor to the final product. Among the subproducts formed during the fermentation stage, total vicinal diketones is the main component, since it is limiting for product transfusion to the subsequent steps, besides having a low perception threshold by the consumer and giving undesirable taste and odor. Due to the instability of main raw materials quality and also process controls during fermentation, the development of alternative forms of beer production without impacting on total fermentation time and final product quality is a great challenge to breweries. In this work, a prior acidification of the pasty yeast was carried out, utilizing for that phosphoric acid, food grade, reducing yeast pH of about 5.30 to 2.20 and altering its characteristic from flocculent to pulverulent during beer fermentation. An increase of six times was observed in amount of yeast cells in suspension in the second fermentation stage regarding to fermentations by yeast with no prior acidification. With alteration on two input variables, temperature curve and cell multiplication, which goal was to minimize the maximum values for diketones detected in the fermenter tank, a reduction was obtained from peak of formed diacetyl and consequently contributed to reduction in fermentation time and total process time. Several experiments were performed with those process changes in order to verify the influence on the total fermentation time and total vicinal diketones concentration at the end of fermentation. This experiment reached as the best production result a total fermentation time of 151 hours and total vicinal diketone concentration of 0.08 ppm. The mass of yeast in suspension in the second phase of fermentation increased from 2.45 x 106 to 16.38 x 106 cells/mL of yeast, which fact is key to a greater efficiency in reducing total vicinal diketones existing in the medium, confirming that the prior yeast acidification, as well as the control of temperature and yeast cell multiplication in fermentative process enhances the performance of diketones reduction and consequently reduce the total fermentation time with diketones concentration below the expected value (Max: 0.10 ppm) / Dentre os principais desafios que se apresentam no mercado industrial de produ??o de cerveja nos dias atuais, podemos citar o abastecimento do mercado com o menor custo poss?vel e com qualidade, visando garantir as expectativas dos clientes e consumidores. A etapa de fermenta??o da cerveja representa aproximadamente 70% de todo o tempo necess?rio para sua produ??o, tendo uma obrigatoriedade de rigorosos controles de processo, para n?o se tornar gargalo da produ??o de cerveja. Essa etapa ? respons?vel pela forma??o de uma s?rie de subprodutos, os quais, ao mesmo tempo em que s?o determinantes da composi??o do buqu? de aromas existentes na cerveja, se produzidos em maior quantidade, podem passar para o produto final sabor e odor desagrad?veis. Dentre esses subprodutos, as dicetonas vicinais totais constituem o principal componente, uma vez que, al?m de serem limitantes quanto ? trasfega do produto para as etapas subsequentes, possuem um baixo limiar de percep??o pelo consumidor e passam sabor e odor desagrad?veis. Devido ? instabilidade da qualidade das mat?rias primas principais e dos controles de processo durante a fermenta??o, o desenvolvimento de formas alternativas de produ??o de cerveja com impactos positivos no tempo total de fermenta??o e na qualidade do produto final, ? um grande desafio dentro das cervejarias. Neste trabalho, foi realizada uma acidifica??o pr?via do fermento pastoso, utilizando-se, para isso, ?cido fosf?rico, grau aliment?cio e reduzindo-se o pH do fermento de aproximadamente 5,30 para 2,20. Al?m disso, com intuito de minimizar os valores m?ximos encontrados de dicetonas totais no tanque fermentador, foram alteradas duas vari?veis de entrada: a curva de temperatura e a multiplica??o celular. Obtiveram-se, como melhores resultados, o tempo total de fermenta??o de 151 horas e concentra??o de dicetonas totais de 0,08 ppm. Desta forma, foi confirmado que a acidifica??o pr?via do fermento, bem como o controle de temperatura e multiplica??o celular no processo fermentativo, aumentam a performance do processo atrav?s da redu??o das dicetonas totais e conseq?entemente, a redu??o do tempo total de fermenta??o com concentra??o de dicetonas abaixo do valor esperado (Max: 0,10 ppm)

Made available in DSpace on 2015-05-14T13:21:09Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3983986 bytes, checksum: 7333ac7eafa0997c880fac1331321936 (MD5) Previous issue date: 2011-06-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work reports the synthesis, characterization, and investigation of the photoluminescent properties of β-diketonate complexes (TTA= 2-thenoyltrifluoroacetonate and DBM = dibenzoylmethanate) of trivalent lanthanides (Ln3+ = Eu3+, Tb3+ and Gd3+ ) with different phosphine oxides ligands (TPPO = triphenylphosphine oxide and HMPA= hexamethylphosphoramide). The elemental C, H, and N analyses, and complexometric titration suggested the general formulas [Ln(TTA)2(NO3)L2], [Ln(DBM)2(NO3)L2], [Ln(DBM)(NO3)2(HMPA)2], [Ln(TTA)3L2] e [Ln(DBM)3L], where L is phosphine oxide ligand. The absorption spectra in the infrared region showed that the coordination of β-diketonate and phosphine oxide ligands to Ln3+ ions occurs through the oxygen atoms of the carbonyl and P = O groups, respectively. Molar condutivity measurements show that the compounds behave as non-electrolytes in solution for the solvents methanol and acetone. The complex Tb(TTA)2(NO3)(TPPO)2 was obtained as single crystals and its structure was resolved by X-ray diffraction. The split transitions 5D0→7FJ, in general, are consistent with a chemical environment of low symmetry around the Ln3+ ion. The phosphorescence spectra of the Gd3+complexes showed the triplet state (T) bands of the ligands TTA and DBM, which were increased in energy (of the triplet state) in the bis- and mono-diketonate complexes in comparison with the tris-diketonates analogous. The tris-diketonate complexes of TTA and DBM showed a higher value of intensity parameters Ω2 when compared with their respective mono-and bis-diketonate, reflecting a chemical environment more polarizable around the ion Ln3+ to these complexes. / Este trabalho relata a síntese, caracterização e a investigação das propriedades fotoluminescentes de complexos β-dicetonatos (TTA=2-tenoiltrifluoroacetonato e DBM= dibenzoilmetanato) de íons lantanídeos trivalentes (Ln3+= Gd3+, Eu3+ e Tb3+) com diferentes ligantes fosfinóxidos (TPPO= trifenilfosfinóxido e HMPA= hexametilfosforamida). Os dados de microanálises de CHN e titulação complexométrica foram concordantes com as fórmulas gerais [Ln(TTA)2(NO3)L2], [Ln(DBM)2(NO3)L2], [Ln(DBM)(NO3)2(HMPA)2], [Ln(TTA)3L2] e [Ln(DBM)3L], onde L é um ligante fosfinóxido. Os espectros de absorção na região do infravermelho evidenciaram que a coordenação dos ligantes β-dicetonatos e fosfinóxidos aos íons Ln3+ ocorre por meio dos átomos de oxigênio dos grupos carbonila e P=O, respectivamente. As medidas de condutividades molares mostraram que os compostos comportam-se como não-eletrólitos em solução para os solventes metanol e acetona. O complexo Tb(TTA)2(NO3)(TPPO)2 foi obtido na forma de monocristais e sua estrutura foi resolvida pelo método de difração de raios-X. Os desdobramentos das transições 5D0→7FJ nos espectros dos complexos de Eu3+, de um modo geral, estão concordantes com um ambiente químico de baixa simetria em torno do íon Eu3+. Os espectros de fosforescência dos complexos de Gd3+ apresentam as bandas do estado tripleto (T) dos ligantes TTA e DBM, onde foi observado um aumento de energia do estado tripleto nos complexos bis e mono-dicetonatos em comparação com os análogos tris-dicetonatos. Os complexos tris-dicetonatos de TTA e DBM apresentaram um maior valor do parâmetro de intensidade experimental (Ω2) quando comparados com os seus respectivos bis- e mono-dicetonatos, refletindo um ambiente químico mais polarizável em torno do íon Eu3+ para estes complexos.