Juan Padilla

Single-crystal EPR studies of a spin-frustrated imidazolate-bridged trinuclear copper(II) complex

Abstract The single-crystal and polycrystalline powder EPR spectra of the trinuclear compound [L 3 Cu 3 (Im) 3 ](ClO 4 ) 3 , L = 1,4,7-trimethyl-1,4,7-triazacyclononane, and Im = imidazolate, have been measured in the temperature range 4.2–300 K. The spectra are explained based on the spin-frustration, the low symmetry, and the intercluster exchange interactions.

Physicochemical Properties and Theoretical Modeling of Actinide Complexes with a para-tert-Butylcalix [6]arene Bearing Phosphinoyl Pendants. Extraction Capability of the Calixarene toward f Elements

The coordination ability of the hexaphosphinoylated p-tert-butylcalix[6]arene B6bL6 toward actinides is established, as well as its good separation ability of the actinide ions UO2 2+ and Th(IV) over trivalent rare earths such as La(III), Eu(III), and Y(III). Spectrophotometric titration of uranyl with B6bL6 in CH 3CN yields log beta 11 = 7.1 and log beta 12 = 12.5 for the 1:1 and 1:2 (UO2 2+/B 6bL6) species, respectively. Actinide complexes with 1:1 and 1:2 (M/L) stoichiometries are isolated and characterized by elemental analysis, IR, and UV-vis. Compounds 1 and 3 fulfill their CN = 8 just with B 6bL (6), while compounds 2 and 4 require coordinated nitrates and/or water molecules. The luminescence spectra of the uranyl complexes and the parameters such as FWMH, vibronic spacing (upsilon sp), and the U-O bond length, as well as the luminescence lifetimes, permit the understanding of the coordination chemistry of these actinide calixarene complexes. Energy transfer from the B6bL6 ligand to the uranyl ion is demonstrated to be relevant in compound 1 with Q abs = 2.0%. The uranyl complex emission reveals a biexponential decay with tau s from 210 to 220 micros and tau L from 490 to 650 micros for compounds 1 and 3, respectively. The liquid-liquid extraction results demonstrate the good extraction capability of B 6bL (6) toward actinides but not for rare earths at room temperature. The extracted species keeps the 1(cation)/1(calixarene) ratio for the UO2 2+, Th 4+, and Eu 3+ ions. A good capacity of B6bL 6 toward Th4+ ions using aqueous phase 2 containing even up to 0.3 M thorium nitrate and an organic phase of 2.47 x 10 (-4) M B6bL6 in chloroform is found. The spectroscopic properties of the isolated uranyl complexes and the extraction studies reveal a uranophilic nature of B6bL6. The molecular modeling results are in good agreement with the experimental findings.

Labelling of Re-ABP with 188Re for bone pain palliation

Etidronate and medronate have been labelled with technetium-99m (99mTc-HEDP, 99mTc-MDP) for bone scanning and, with rhenium-188 (188Re-HEDP) to palliate the pain resulting from bone metastases. The objective of this study was to label alendronate, ABP, a new bisphosphonate, with SnF2-reduced-188Re. The reagents for the 5 mg ABP kit were SnF2, KReO4 and gentisic acid at acid pH. The chemical, spectroscopic and microscopic characteristics, quality control, rat bone uptake of [188Re]Re-ABP and similarities with 99mTc-ABP are presented. We conclude that this is a promising new radiopharmaceutical for bone metastases pain palliation.

NEW MONONUCLEAR LANTHANIDE(III) MACROCYCLIC POLYMERIC COMPLEXES WITH THE 1,5,9,13-TETRAAZACYCLOHEXADECANE LIGAND: THEIR MAGNETIC STUDIES AND SEMIEMPIRICAL CALCULATIONS

Abstract Novel mononuclear lanthanide polymeric complexes are formed with Nd(III), Eu(III), Gd(III), Tb(III), Er(III) and Lu(III) nitrates and the 1,5,9,13-tetraazacyclohexadecane ligand. These compounds were characterized by elemental and thermal analysis, IR, EPR, 1H and 13C NMR spectroscopies and magnetic susceptibility at variable temperature. The molecular weight of the compounds was determined by gel permeation chromatography, the results of which 6272 are 6120 and 4121 g/mol for Nd(III), Gd(III) and Er(III) compounds, respectively. The structures for the monomeric unit and the polymers were calculated by the force—field method. Each lanthanide compound showed specific and unusual magnetic properties which were associated with the particular arrangement of the elemental units in each polymer.

ESR study of lithium nitrate irradiated with gamma-rays with total doses from 10 to 100 Mrad

Natural non-pretreated polycrystalline lithium nitrate was irradiated by gamma-rays of60Co with total radiation doses from 10 to 100 Mrad, at room temperature. No color centers were observed in samples irradiated in this range. X-ray and infrared studies evidenced the distortion of the lattice planes. In general, the following species were detected NO2, NO3 radicals, and NO22−, NO32−, O2− ionic radicals.

Structure Sensitivity of Sol-Gel Alkali Tantalates, ATaO3 (A= Li, Na and K): Acetone Gas Phase Condensation

Perovskite-type compounds such as alkali tantalates, ATaO3 (A = Li, Na and K), prepared by the sol-gel method are reported as heterogeneous basic catalysts for the acetone aldol condensation. It has been proposed that the activity order and the selectivity patterns (LiTaO3 > > KTaO3 > NaTaO3) depend on the octahedral arrangements of the TaO6 tantalates.

Radiolysis influence on the tritium content in irradiated lithium nitrate for fluorine-18 production using a nuclear reactor

Abstract Natural non pre-treated polycrystalline lithium nitrate suffered radiolysis by cobalt gamma-rays, 2.65 and 3.37 MeV protons, β-particles from 3H and nuclear reactor irradiation at room temperature. The sample irradiated in the nuclear reactor was a deep reddish-orange, and contrary to what was expected, this colour was stable, disappearing only after annealing or dissolution. These colour centres, seemingly F2 centres, are produced by neutrons, tritons and alfa-particles and are diamagnetic since the paramagnetic Electron Spin Resonance (ESR) signal centred at 2.009 did not change after annealing. This study suggests that radiolytical products might be NO2, NO3, NO2- 3, NO2- 2 radicals and NO1- 2. The high content of tritium in the lithium nitrate irradiated in the nuclear reactor is promoted by these radicals and defects which act as trapping centres for tritons.

Anatase-Rutile Phase Transformation of Cu2+ Doped TiO2 in a Non-Reducing Atmosphere

The anatase-rutile phase transformation of TiO2 containing various Cu2+ amounts of Cu ions was investigated in argon atmosphere by means of X ray diffraction and electron spin resonance spectroscopy. The samples were prepared by the sol-gel method from titanium(IV) isopropoxide and copper(II) nitrate. The amorphous samples were calcined in argon atmosphere for 2 h at different temperatures. In the presence of Cu2+, the anatase-rutile transition temperature is lower than the corresponding one in pure TiO2. The transformation in argon atmosphere changes the transition temperatures due to the spontaneous reduction of Cu2+ and Ti4+ ions to metallic copper and Ti3+ respectively. The broadening of the electron spin resonance spectra from this ion show that Ti3+ ions are present in different sites into the TiO2 lattice. This are confirmed by electron spin resonance and allowed us to follow the phase transformation in detail.