Irina S. Pekareva

Influence of ligand architecture on the structure of coordination centre in dimeric europium carboxylates with 1,10-phenanthroline

Abstract Methods of optical spectroscopy and X-ray crystallography data were used to examine the effect of architecture of carboxylate anions on structure of the Eu3+ coordination centre in europium carboxylates with 1,10-phenanthroline Eu(RCOO)3·Phen. Luminescence spectra of europium acetate, nitropropionate, benzoate, naphthylcarboxylates, phenylacetates, phenoxyacetate, triphenylpropionate were investigated. A few of europium carboxylates with 2,2′-bipyridine Eu(RCOO)3·Bpy and europium salts Eu(RCOO)3·nH2O were also studied. Vibrational IR and Raman spectra of phenylacetate family were analyzed. The crystal structure of nitropropionate Eu(NO2C2H4COO)3·Phen was solved by X-ray diffraction method. The predominant influence of steric hindrances on Eu3+ coordination centre was observed at increase of the size of aromatic fragment of carboxylate anions. It was demonstrated, that introduction of the methylene bridges between the carboxylic group and aromatic rings of ligand weakens the effect of steric factor.

Luminescence and structural properties of lanthanide complexes of Schiff bases derived from pyridoxal and amino acids

Lanthanide complexes of Schiff bases (SBs) with 1:1 and 1:2 (M:Lig) stoichiometric ratios were prepared by condensation of pyridoxal (PL) and aspartic acid (Asp) or l-histidine (His), respectively, in the presence of the appropriate metal chloride as a templating agent. These complexes were studied by optical spectroscopy and single crystal X-ray diffraction techniques. Crystallographic studies of 1:1 ([Eu(PL-Asp)(H(2)O)(4)](H(2)O)) and 1:2 ([Eu(PL-His)(2)(H(2)O)(2)]Cl(H(2)O)(4)) complexes show that Eu(III) is eight-coordinate in both structures, in a distorted square antiprism environment formed by the phenolic oxygen of PL, the nitrogen atom of carbon-nitrogen double bond, oxygen atoms of the carboxylate groups of His or Asp, and oxygen atoms of the water molecules. The main species formed in aqueous solutions containing these SBs have been determined by analysis of the luminescence spectra, lifetimes of Eu(III) excited states and vibronic interaction as well as structural features of the Eu(III) coordination sphere. Possible tetradentate coordination function of SBs in aqueous solutions with relatively high concentrations as well as the potential application of the lanthanide SB complexes as new luminescence materials are discussed.

Characterisation of geometric isomers of europium chlorides with 2,2′-bipyridine based on X-ray diffraction, luminescence and quantum chemical data

A low-temperature high-resolution luminescence study of the EuCl3bpy2(H2O) n isomers has been carried out. The Eu3+ luminescence spectra of all geometric isomers were recorded over the spectral range which includes transitions from the 5D0 excited state to the 7F0–4 ground state manifolds and from the 5D1 excited state to the 7F0–2 ground state manifolds. Analysis of the Eu3+ transitions observed in the luminescence spectra shows that the Eu3+ ion occupies a spectroscopic site symmetry that approaches a C2 v symmetry with distortion towards C2 or lower symmetry. The structural features and distortions of the Eu3+ coordination polyhedron in these geometric isomers were described based on the X-ray crystallographic data as well. The splitting patterns and energies found of the 7F0–4 manifolds have been used to calculate the crystal field parameters (CFPs) of the Eu3+ ions in these geometric isomers. In addition the mutual influence of the ligands as well as the relative stability of geometric isomers of the [EuCl3bpy2(H2O)2]+ cation in the gas phase was analyzed within DFT calculations.

The substituted [2.2] paracyclophanes as versatile platform for a design of new optical materials

The series of novel unsymmetrical β--diketones substituted by functional groups with different donor-acceptor properties, as well as of their lanthanide complexes have been synthesized for the first time. The optical properties of these [2.2]paracyclophane-derived ligands and the lanthanide complexes were studied by UV-visible and luminescence spectroscopy. The energy of absorption maximum of these β--diketones correlates with donor-acceptor properties of functional groups and a size of the conjugated system. All β--diketonates synthesized exhibit broad emission spectra with red shifted maxima in comparison with isolated [2.2]paracyclophane moiety. The designed blue-emitting unsymmetrical β-diketones act as very efficient sensitizers of the Eu3+ emission with excitation wavelength up to 450 nm. Nonlinear optical properties have been studies for some β--diketones as well. Their average NLO susceptibility was found comparable with that of such well known NLO crystal as PNP.

NLO properties of formyl-methoxy derivatives of [2.2] paracyclophane containing the donor group in different positions

Formyl-methoxy derivatives of [2.2]paracyclophane (pCp) have been synthesized and studied by optical spectroscopy as well as the X-ray diffraction method. These molecules crystallize in acentric space groups. The efficiency of SHG ability of these compounds was measured by the powder technique at 1064 nm fundamental wavelength and average NLO susceptibility for some of them was found comparable with such well-known NLO crystal as NPP. The calculations of molecular and crystalline nonlinearities within density functional theory using M052X/6-31+G* level of approximation were also conducted for the considered series of compounds.