Maria Teresa Alonso

Synthesis and luminiscence properties of europium(III) and terbium(III) complexes with polyacid chelates derived from 2,6-bis(N-pyrazolyl)pyridine

A short and efficient synthesis of N, N, N′, N′-[2,6-bis(3-aminomethyl-1-pyrazolyl)pyridine]-tetrakis(acetic acid)(6), an analogue of terpyridine with additional chelating iminodiacetic groups, is described. Compound 6 forms stable complexes with EuIII and TbIII in water whose relative luminescence yields, excitation maxima and emission decay lifetimes have been measured. The number of water molecules in the first coordination sphere of the europium complex have also been determined. Comparison of data from the EuIII and TbIII complexes of 6 and of the parent trisheterocycle diacid 2,6-bis(3-carboxy-1-pyrazolyl)pyridine shows that the iminodiacetic subunits give extra stabilization to the complexes and are essential to protect the metal from the water environment.

Synthesis and complexation properties of 3-Aroylcoumarin crown ethers. A new class of photoactive macrocycles.

Abstract Synthesis of fluoroionophores consisting of 3-benzoylcoumarins fused with crown ethers in two different modes are described. The resulting macrocycles bore emission properties strongly dependent on metal ions and coumarin substitution and may be therefore used as cation dependent fluorescence signaling systems or triplet sensitizers for lanthanide luminescence.

Palladium(II) coordination and cyclometallated complexes derived from 3- and 5-aryl-substituted pyrazoles

Palladium(II) coordination complexes of nine 3- or 5-arylpyrazoles (phenyl, 2-bromophenyl, or 3-methoxyphenyl), as well as of 3,5-diphenylpyrazole, are reported. A cis-trans mixture of [PdL2Cl2] isomers is found in the case of 3-aryl-1-methylpyrazoles, the cis-isomers being transformed into trans by heating. Only trans isomers are isolated with the other ligands. Cyclopalladation of 3-ary]-1-methylpyrazoles can be performed with palladium(II) acetate, and the resultant μ-acetate bridged dimers can be transformed into μ-chloro bridged dimers or acetylacetonate monomers. The structures of the complexes have been characterized by 1H- and 13C-NMR spectroscopy.

Unusual behaviour of 7-diethylamino-3-(3,4-ethylen-dioxybenzoyl)coumarin towards Group IIA cations: A potential photoactive probe for magnesium

Abstract The titled compound showed, upon spectrophotometric titrations with Group IIA cations, a spectacular bathochromic shift (c.a. 50 nm) with Mg2+ but not with the other cations. This result is understood in terms of internal charge-transfer species expressly favored by Et2N and ArCO substituents and best matching of ionic diameter and charge density of Mg2+. This finding may lead to new simple photoactive probes.

The discovery of a simple ligand based on acetophenone bearing excellent quantum yields for the excitation of Eu3+ and Tb3+

Abstract A new, relatively simple tetra-acid ligand derived from acetophenone was synthesized and its luminescence properties when forming Eu(III) and Tb(III) chelates were evaluated in aqueous and methanol solutions. The titled compound displayed excellent quantum yields of triplet sensitization of lanthanide luminescence (0.20–0.25 for Eu 3+ and 0.95–1.00 for Tb 3+ ). Results suggested that the metal and the cromophore should be in close contact and that the iminodiacetic arms isolate very well the metal from the surrounding OH oscillators which normally quench lanthanide luminescence.

Novel polyaminocarboxylate chelates derived from 3-aroylcoumarins

Abstract We have devised efficient reaction pathways to attach aminopolycarboxylate subunits to the 3-aroylcoumarin chromophore. Two series of compounds were thus prepared in which the chelating arms were directly bonded to the coumarin ring (series A) or to the 3-aroyl moiety (series B). The corresponding Eu(III) and Tb(III) chelates were easily formed and their photophysical properties measured. In all the cases, lanthanide emission lifetimes were in the range of ms. Unfortunately, quantum yields were relatively low. Measurement of T1 states gave too low range of values to sensitize Tb(III). In fact, the metal emission of Tb(III) chelates of series A was not observed. However, series B was able to sensitize both metals. The absorption/energy-transfer/emission mechanisms are discussed.

Palladium(II) coordination and cyclometallated complexes derived from 1-tert-butylpyrazole

The synthesis and characterization of a number of new coordination compounds of PdII with the nitrogen donor 1-tert-butylpyrazole (tBuPzH) are described. Compounds are trans-[Pd(tBuPzH)2Cl2] and the cyclometallated structures [Pd2(tBuPz)2(AcO)2] and [Pd3(tBuPz)2(AcO)4]. All these complexes are mixtures of syn and anti isomers. Also, the chloro-bridged complex [Pd2(tBuPz)2Cl2] has been isolated as an equilibrium mixture of cis and trans isomers. The compounds have been studied by variable temperature 1H- and 13C-NMR spectroscopy.

Cyclometallated compounds of Pd(II) with pyrazole derivatives. Unusual double palladation of diarylbis(N-pyrazolyl)methanes

Abstract Reaction between palladium(II) acetate and bis(arylpyrazolyl)methanes with two aryl groups 3-RC 6 H 4 , 2a–c or the 3-RC 6 H 4 and one 5-RC 6 H 4 , 3a–c (R = H, 3′-OCH 3 , or 2′-Br) 3a–c in refluxing acetic acid, affords metallacycles of stoichiometry LPd 2 , with two different five- and six-membered palladacycles, one containing an aromatic carbon-metal bond and the other a pyrazole carbon-metal bond, repectively. Treatment of acetate-bridged palladacycles 5a–c and 6–c with Tl(acac) yields monomeric products 7a–c and 8a–c of formula [LPd 2 (acac) 2 ]. The products have been characterized by elemental analysis (C, H, N) and NMR spectroscopy. The preferential formation of a six-membered metallacycle in the first step of the reaction is discussed.

Luminescent cryptands. 3-aroylcoumarin macrobicyclic complexes of europium(III) and terbium(III): the effect of coumarin substitution.

Substituted 3-aroylcoumarins incorporated in a polyethylenoxy cryptand (2.2.2) by the 3-aroyl group were synthesized with the purpose of developing new markers to be used in time-resolved fluorimetric bioaffinity assays based on the unique luminescence properties of Eu(III) and Tb(III) ions. Some spectral properties and luminescence intensities of the complexes were measured in acetonitrile and MeOH. The mechanism of metal sensitization depended on lanthanide and will be discussed in detail.

Synthesis and luminiscence properties of europium(III) and terbium(III) complexes of aminopolycarboxylic acid ligands containing 3-aroylcoumarin

Abstract Three differently substituted 3-aroylcoumarins, L 1–3 , with tetraacid chelating subunits anchored at the 3-benzoyl group were synthesized, and their complexes with Eu 3+ and Tb 3+ formed as new potential bioaffinity-assay markers. Some spectral and luminescence properties of the complexes in water and methanol are reported.