Iliana C. Muñoz

Syntheses of new 15-membered and 16-membered macrocyclic ligands with three pendant acetato groups and the structures of the gadolinium(III) complexes

Abstract A condensation of diethylenetriaminepentaacetic dianhydride with ethylenediamine gave a 15-membered macrocyclic ligand with three pendant acetato groups, (15-dtpa-en)H3C10H18N5O2(CH2CO2H)3; a l6-membered analogue, (l6-dtpa-pn)H3 C11H20N5O2(CH2CO2H)3, was obtained by the use of propanediamine instead of ethylenediamine. The structures of their gadolinium(III) complexes, Gd2(15-dtpa-en)2·16H2O and Gd(16-dtpa-pn)·4H2O, were determined by X-ray analyses. Gd2(15-dtpa-en)2·16H2O crystallized in the orthorhombic space group Pbca with: a=18.205(1), b=18.930(1) and c=15.609(1) A. Two Gd(III) ions are located between two ligand molecules, forming a binuclear metal chelate molecule with a center of inversion. The coordination geometry around a metal ion is described as a distorted tricapped trigonal prism that consists of nine coordinated atoms. Gd(l6- dtpa-pn)·4H2O crystallized in the monoclinic space group P21/c with: a =8.246(2), b = 14.995(3), c= 19.367(4) A and β = 90.258(2)°. In this compound, a water molecule and a single ligand molecule are coordinated to a Gd(III) ion, forming a mononuclear chelate with a tricapped trigonal prism. The structural differences between the two Gd(III) complexes are a result of the differences in the favorable conformations assumed by the two macrocyclic ligands.

X-ray structures and fluorescence spectra of binuclear Zn2+ and Cd2+ complexes of an amide-based naphthalenophane

Abstract The formation of binuclear Zn2+ and Cd2+ complexes with an amide-based chelating naphthalenophane has been confirmed by X-ray crystal analyses: the complexes are formulated as [(H2O)MLM(OH2)]0 (M=Zn or Cd), and the naphthalenophane, LH4, is 2,9,22,29-tetraoxo-4,7,24,27-tetrakis(carboxymethyl)-1,4,7,10,21,24,27,30-octaaza[10.10](1,5)naphthalenophane. The Zn2+ complex has a six-coordination geometry and the Cd2+ complex has a seven-coordination geometry. The naphthyl groups are deformed from the planar structure by metal complexation in both complexes. Fluorescence from the uncoordinated ligand is weakened by protonation. The coordination of Zn2+ enhances the fluorescence whereas the coordination of Cd2+ weakens the emission: the intensity ratio, F(L):F(Zn2L):F(Cd2L)=1:12:0.2 at pH 10. The Zn2+ complex exhibits a large change in the fluorescence intensity with pH, as a result of interconversion between [(H2O)ZnLZn(OH2)]0 and [(HO)ZnLZn(OH)]2−; the emission of the latter formed at higher pH is 20 times stronger than that of the former formed at lower pH. Structural changes that occur in the chelating units upon protonation or metal complexation propagate to the fluorescent units through the amide groups that link the two functional units. This propagation results in the fluorescence properties characteristic of the amide-based naphthalenophane.

Structural and spectroscopic studies of binuclear Cu2+ and Co2+ complexes with an amide-based naphthalenophane

Abstract Binuclear Cu2+ and Co2+ complexes with a chelating naphthalenophane were characterized by single-crystal X-ray analyses, electronic absorption spectroscopy and luminescence spectroscopy: the naphthalenophane is 2,9,22,29-tetraoxo-4,7,24,27-tetrakis(carboxymethyl)-1,4,7,10,21,24,27,30-octaaza[10.10](1,5)naphthalenophane (abbreviated as LH4). The Cu2+ complex crystallized as [Cu2L]0 from acidic solution and [Cu2(LH−4)]4− from basic solution: the coordination geometry around each metal ion in [Cu2L]0 is a square pyramid with an amide oxygen atom, two amino nitrogen atoms and two carboxylate oxygen atoms; the amide nitrogen atoms in [Cu2(LH−4)]4− are deprotonated and construct a square planar coordination geometry together with amino nitrogen atoms around each metal ion. The formation of the two structures is due to a change in the coordination linkage of the amide groups. [Cu2(LH−4)]4− shows strong metal–ligand charge transfer bands caused by the coordination of the amide nitrogen atoms that are directly bonded to the naphthyl groups. In the Co2+ complex, [Co2L(H2O)2]0, each metal ion has a seven-coordination geometry; the emission and excitation bands in the luminescence spectra showed a red shift upon metal complexation. In all metal complexes studied, the naphthyl groups are distorted from the planar structure, as a result of metal complexation that causes contraction of the macrocyclic rings.

Thermoluminescence property of LiMgF3 erbium activated phosphor

The perovskite-like LiMgF(3):ErF(3) pellets were obtained from the melt formed by LiF and MgF(2) mixed salts in the stoichiometric ratio. The perovskite material was doped with 1, 2 and 4 mol% of ErF(3) impurity. The pellets samples were (60)Co gamma irradiated and their thermoluminescence (TL) properties were analyzed, i.e., dose-response, fading at RT and under UV irradiation, TL signal reproducibility, and kinetic parameters. The intensity of the TL response against irradiation dose was increased remarkably by the high concentration of impurity, and a linear dose-response was observed in the range of 1-10 Gy. The fading observed at RT was about 10-30% after 24h from irradiation. All samples were exposed from 1 to 200 Gy gamma dose range. The TL glow peaks were found around 367-376, 438-447, 509-521, and 594-611 K, when the doped samples were 1, 2 and 4 mol% of the erbium impurity concentration. The thermoluminescence kinetics parameters of the glow curves have been analyzed using the Computerized Glow Curve Deconvolution (CGCD) method.

Metal–ligand interactions in benzodioxotetraaza-macrocyclic metal chelates

Abstract Reactions of ethylenediaminetetraacetic (edta) dianhydride with o-phenylenediamine (od) and 9,10-diaminophenanthrene (phn) gave (edtaod)H2 and (edtaphn)H2, respectively, in which a chelating edta unit and an aromatic diamine unit are linked by two amide bonds. The complexation of these new 12-membered macrocycles with transition metal ions was studied by X-ray crystallography, potentiometric titrations, UV–Vis absorption spectroscopy and fluorescence spectroscopy. The absorption spectra are sensitively changed by metal complexation. The spectral changes are the most significant for the Cu2+ complexes, and are well correlated with the species distribution diagram. The X-ray study of the Cu2+ complex, [Cu(edtaod)]0, has shown that a square plane is formed around the central metal ion by an amide oxygen atom, a carboxylate oxygen atom and an amino nitrogen atom from a ligand molecule and a carboxylate oxygen atom from the adjacent chelate molecule. The amide nitrogen atoms in [Cu(edtaod)]0 are readily deprotonated and result in the formation of [Cu(edtaodH−1)]− and [Cu(edtaodH−2)]2− in neutral and basic media. The coordination of deprotonated amide nitrogen atoms to a Cu2+ ion leads to a strong metal–ligand interaction, which causes an intense charge-transfer band in [Cu(edtaodH−1)]−, new UV absorption bands in [Cu(edtaodH−2)]2− and the effective quenching of emission in the Cu2+ complex of (edtaphn)H2.

Pyrene bichromophores composed of polyaminopolycarboxylate interlink: pH response of excimer emission

Fluorescent response to pH has been studied on water-soluble pyrene-based bichromophores, (edtapy)H2 and (dtpapy)H3, in which two pyrenyl groups are linked by an ethylenediaminetetraacetate (EDTA) and a diethylenetriaminepentaacetate (DTPA) unit, respectively, through amide linkages. The excimer emission of the EDTA derivative is strengthened sharply with increasing pH at two steps; the first step is associated with the dissociation of acidic hydrogen from amino nitrogen in partially protonated species (edtapy)H− and the second step is attributable to the amide group. The excitation spectra have evidenced the formation of a static excimer in the ground state of completely deprotonated species (edtapy)2 − . The close contact between pyrenyl groups in (edtapy)2 − has been confirmed by density functional theory, which has also shown that the close contact is broken when amino nitrogen is protonated. The DTPA derivative exhibits a strong excimer emission, which shows an intensity–pH profile of an ‘off–on–off–on’ type. This rare pH response is ascribable to multiple protonation sites in the DTPA chain, as confirmed by 1H NMR. The novel pH-sensing capabilities in specific pH regions are due to the combination of the fluorescent group with the polyaminopolycarboxylate chains whose conformations are reversibly altered by protonation–deprotonation processes.

Polymerization of anilines by the use of copper(II) perchlorate as an oxidative coupling agent

SummaryPolyaniline and polyalkylaniline perchlorates were prepared by oxidative coupling polymerization of anilines by the use of copper(II) perchlorate in acetonitrile as an oxidant. The corresponding polymer bases obtained by treating the perchlorates with alkaline solution were soluble in dimethylsulfoxide and partly soluble in tetrahydrofuran. The molecular weights of the THF-soluble components were 2000–6000. The charge transport of the perchlorates is influenced by the chain length and the steric effect of alkyl substituents.

Thermoluminescence response and glow curve structure of Sc2TiO5 ß-irradiated

Discandium titanate (Sc2TiO5) powder was synthesized in order to analyze its thermoluminescence (TL) response. The TL glow curve structure shows two peaks: at 453-433 K and at 590-553 K. The TL beta dose-response has a linear behavior over the dose range 50-500 Gy. The T(stop) preheat method shows five glow peaks that were taken into account to calculate the kinetic parameters using the CGCD procedure. TL results support the possible use of Sc2TiO5 as a new phosphor in high ß-dose dosimetry.

Thermoluminescence of Beta Particle Irradiated LiMgF 3 :X (X=Ce, Er)

The thermoluminescence (TL) properties of beta particle irradiated Ce and Er doped LiMgF 3 phosphors are presented. Pellet-shaped samples were prepared by cool-pressing 74 μm size particle powder, followed by thermal annealing at 700 °C during 5 h in air atmosphere. Some samples were irradiated with beta particles in the dose range from 8 up to 128 Gy. The sensitivity of Er doped samples was greater than the one of Ce-doped. In both cases, a 2 % mol of dopant concentration was used. The TL fading was between 19 % for Ce-doped samples, and 24 % for the Er-doped. The integrated TL increases as dose increases, with no saturation clues. The TL sensitivity of samples exhibited a loss in successive irradiation – readout cycles.