P.C. Isolani

Terras raras: aplicações industriais e biológicas

The history of the rare earths is rich in innovation and these elements have been the object of study of a number of scientists. Rare earths are used practically in almost all aspects of life and these applications are due to their outstanding properties, mainly spectroscopic and magnetic. In industry, the applications of rare earths are many, such as in catalysis, phosphors, magnetism, glass and lasers. In biological systems, rare earths are used, for example, as luminescent probes in the investigation of binding sites in proteins, labels in immunoassays and in noninvasive tests.

Energy requirements for the indirect formation of cluster ions in the gas phase: the ion-molecule reaction of negative ions with esters of formic acid

Abstract Negative ions are shown to lead to solvated ions in the gas phase by reaction with esters of formic acid when two requirements are met: (1) the bond energy of the cluster is greater than 9.3 kcal/mole, and (2) the proton affinity of the negative ion is greater than 349 kcal/mole. A likely mechanism for the bimolecular process is suggested based on these results.

NEODYMIUM(III) AND EUROPIUM(III) PICRATE COMPLEXES WITH 2-AZACYCLONONANONE: SPECTROSCOPY AND STRUCTURE

Abstract Complexes with composition Ln(pic)3·3(aza) (Ln = Nd, Eu; pic = picrate; aza = 2-azacyclononanone) were characterized by IR absorption spectroscopy and elemental analysis. Visible absorption spectra for the Nd compound and emission spectra for the Eu compound were also recorded. X-ray single crystal diffraction analysis of the Eu compound shows that the picrates are bidentate, bonded through the phenolic and one o-nitrogroup oxygens and the 2-azacyclononanones are bonded through the carbonyl oxygens, forming a tricapped trigonal prism with D3h symmetry distorted towards C3v around the EU3+ ion, which is in agreement with the emission spectra evidence.

Synthesis and structure of lanthanide picrates with trans-1,3-dithiane-1,3-dioxide

Abstract Compounds with the formula [Ln(pic) 3 ( trans -DTSO 2 ) 2 ] (Ln=La–Lu and Y) were obtained by reaction of hydrated lanthanide picrates with trans -1,3-dithiane-1,3-dioxide ( trans -DTSO 2 ) in absolute ethanol. Lanthanide contents were determined by titration with EDTA; CHN were determined by microanalytical procedures. Data are in good accordance with the proposed stoichiometry. IR absorption spectra were interpreted in terms of trans -DTSO 2 and picrate anions coordinated through the oxygen atoms. The parameters obtained from the absorption spectrum of the Nd(III) compound indicate weakly covalent metal–ligand bonds. The emission spectrum obtained at 77 K for the Eu(III) compound suggests a C 2v symmetry for the coordination polyhedron. X-Ray powder patterns show that the compounds are isomorphous. The structure of europium compound was determined by single crystal X-ray analysis and showed that the crystals are triclinic, space group P 1 , a =10.771(1) A, b =12.243(1) A, c =16.415(2) A, α =99.930(10)°, β =103.970(10)°, γ =106.220(10)°. The compound exhibits a polymeric structure, in which two trans -DTSO 2 are bridging the Eu(III) ions. The central ion is octacoordinated to four oxygens of trans -DTSO 2 and four oxygens of one bidentate and two monodentate picrate anions, in a bicapped trigonal prism geometry, the dihedral angle between the bases being 14.2(1) o .

Synthesis, characterization and reactivity of lantahnide(II) poly(pyrazol-1-yl)borates (LnSm, Eu and Yb); fluorescence studies of [EuL2(THF)2] [LB(pz)4, HB(pz)3]; X-ray crystal structures of [Eu{B(pz)4}2(THF)2] and ]Yb{B(pz)4}3]·(2H5OH

Abstract The reaction [LnI2(THF)x] (Ln - Sm, Eu, Yb) with 2 equiv. of K[B(pz)4] (pz = pyrazolyl) in THF resulted in the formation of [Ln{B(pz)4}2(THF)2] complexes. The molecular structure of [Eu{B(pz)4}2(THF)2] has been determined by single-crystal X-ray diffraction analysis. The [Sm{B(pz)4}2(THF)2] and [Yb{B(pz)4}2(THF)2] complexes are fluxional in solution, as indicated by the equivalence of the pyrazolyl rings in the 1H NMR spectra at room temperature. A static spectrum could be obtained for the Sm compound at -68°C with a pattern that is in accordance with the geometry found for the Eu complex, in the solid state. The complexes [{LnHB(pz)3}2(THF)2] (Ln - Sm, Eu, Yb) have been prepared by the procedure used to synthesize the [Ln{B)pz)4}2(THF)2] complexes. The THF molecules can be replaced by 1,2-dimethoxyethane yielding the compounds [{LnHB(pz)3}2(DME)] (Ln = Sm, Yb. [Sm[B)pz)42(THF2] and [Yb{B)pz)4}2(THF)2] react readily with alkyl halides, alcohols or alkynes to yield LnIII complexes that disproportionate to the [Ln{B(pz)4}3] complexes. The crystal structure of the compound [Yb{B(pz)4}3]·C2H5OH obtained in the reaction of [Yb{B(pz)4}2(THF)2] with ethanol was determined by X-ray diffraction analysis. Fluorescence studies on the Eu compounds are also reported.

Studies of neodymium, europium and terbium picrate complexes with benzyl-t-butyl sulphoxide

Abstract Complexes of the formula Ln(pic) 3 ·4L (Ln  Nd, Eu, Tb; pic, picrate; L, benzyl- t -butylsulphoxide) were obtained either by precipitation by ligand addition to a hot aqueous solution of the lanthanide salt or by simply melting a mixture of components (“one-pot” synthesis). The compounds were characterized by Ln titration with EDTA, C, H and N elemental analysis, IR spectra, absorption spectra of the neodymium compound, emission spectra of the europium compound and thermal analysis.

Structure characterization of molecular complexes for non-linear optical materials I. X-ray analysis and AM1 calculations of 1 : 1 complexes of 8-hydroxiquinoline (1) and isonicotinamide (2) with 2,4,6-trinitrophenol

Abstract C6H2N3O7–·C9H8NO+ (1), Mr = 374.27, P21/c, a = 8.2606(9), b = 9.2574(9), c = 19.906(2) Å, β = 91.441(8)°, Z = 4, R1 = 0.0405. C6H2N3O7–·C6H7N2O+, (2), Mr = 351.24, P21/n, a = 14.3064(6), b = 7.4451(7), c = 14.7209(7) Å, β = 116.626(3)°, Z = 4, R1 = 0.0385. The packing units in both compounds consist of hydrogen bonded cation-anion pairs. The basic first and second-level graph set analysis are given. The (hyper)polarizabilities have been calculated for the crystallographic and optimized molecules, by the semi-empirical quantum method AM1.

Synthesis and characterization of lanthanide picrate complexes with tripiperidinophosphine oxide

Abstract Compounds with the general formula Ln(pic) 3 ·2tpppo (Ln: La-Lu, Y; pic=picrate; tpppo=tripipendinophosphine oxide) were synthesized by reaction of the hydrated picrates with tpppo in absolute ethanol. IR absorption spectra were interpreted in terms of the coordination of tpppo through the oxygen and picrate anions that are bidentate, coordinated to the central ions through the phenoxo group and one oxygen of an ortho -nitro group. Conductance measurements in acetonitrile solutions show that the complexes behave as non-electrolytes. X-ray powder patterns show only one isomorphous series. Phosphorus-31 NMR showed a signal shift to lower field with relation to the free ligand, showing evidence of bonding through the phosphoryl group. The parameters obtained from the absorption spectrum of the Nd compound indicate that the metal-ligand bonds present some covalent character. The emission spectra of the europium and samarium adducts were determined. The spectrum of the europium compound was interpreted in terms of D 2d distorted towards C 2v symmetry for the Eu(O) 8 chromophore.

Uranyl nitrate complexes with lactams

Abstract The preparation, characterization and spectroscopy of complexes of uranyl nitrate with the lactams: δ-valerolactam (δ-val, C 5 H 9 NO), e-caprolactam (e-capro, C 6 H 11 NO), 2-azacyclononanone (2-aza, C 8 H 15 NO) and 2-azacyclotridecanone (2-actd, C 12 H 23 NO) are described. They were prepared by reaction of hydrated uranyl nitrate with the ligands in ethanolic solution (molar ratio 1:2) and presented the general composition UO 2 (NO 3 ) 2 .2L, except for the e-capro complex that is dimeric, with composition: (UO 2 ) 2 (NO 3 ) 2 (O 2 )(e-capro) 4 . The peroxo bridge was introduced when 2,2-dimethoxypropane contaminated with peroxide was used to precipitate the crystals. They were characterized by CHN microanalyses, IR spectra, TG and DSC analyses and emission spectra in the visible region. The structure of the e-capro complex was determined by X-ray single crystal analysis.

Synthesis and characterization of polynuclear lanthanide aryloxides

The reactions of europium and ytterbium in liquid ammonia with a solution of 1-naphthol in tetrahydrofuran provide a convenient route to lanthanide aryloxides. The polymetallic lanthanide complexes [Eu 4 (μ-OC 10 H 7 ) 6 (OC 10 H 7 ) 2 (THF) 10 ].2THF 1 and [Yb(μ-OC 10 H 7 )-(OC 10 H 7 ) 2 (THF)(MeCN)] 2 .2MeCN 2 were synthesized and characterized by X-ray diffraction studies.