Harry G. Brittain

Stereoselectivity in the adduct formation between chiral Eu(III) β-diketone complexes and sulphoxides, sulphones and phosphate esters

Abstract The adduct formation which takes place when Eu(III) chelates of triflouroacetyl-d-camphor and heptaflourobutyryl-d-camphor bind substrates has been studied. Enhancement of Eu(III) luminescence as a function of substrate concentration has been used to obtain information on the nature of the chelate/substrate adducts, and the stereochemistry of the complexes was studied by means of circularly polarized luminescence (CPL) spectroscopy. While no optical activity can be measured for, the free chelates, formation of the adduct complexes usually led to the observation of very strong chirality even though the substrates were themselves achiral. It was concluded that adduct formation causes the bulky camphorato ligands to interact and adopt a configuration of lowest energy. This process perturbs the diastereomer ratios and yields a partial resolution of these very labile complexes.

Synthesis and characterization of Eu(III) complexes with chiral Schiff base ligands derived from salicylaldehydes and amino alcohols

Abstract Optically active Schiff base ligands have been formed by the condensation of various salicylaldehydes with a series of chiral amino alcohols. The Eu(III) derivatives of these ligands were obtained as oligomeric materials, exhibiting an empirical 1:1 metal:ligand stoichiometry. The complexes were found to be somewhat soluble in chloroform, where they existed primarily as trimeric species. The optical activity experienced by the Eu(III) ion was observed to be dominated by the presence of configurational effects, corresponding to a dissymmetric arrangement of Schiff base ligands about the Eu(III) ion.

Pfeiffer effect optical activity developed in lanthanide tris(pyridine-2,6-dicarboxylate) complexes by chiral tartrate substrates

Abstract Optical activity has been induced in the title complexes through outer-sphere complexation with L-tartaric acid, and with several carboxyl and hydroxyl esters. The optical activity was studied in the Tb(III) and Eu(III) complexes by means of circularly polarized luminescence (CPL) spectroscopy, and the symmetry changes associated with the adduct formation were followed by examining the hypersensitive absorption of the Ho(III) complexes. Optical activity was found to be induced by each substrate, although the nature of the outer-sphere interaction was necessarily different in the various systems. It was found in every case that the presence of a (R,R)-tartrate substrate led to enrichment of the A-isomer of the lanthanide complexes.

Luminescence studies of lanthanide oxides: I. Thermal and hydration effects on the metal ion site symmetry in Europium oxide catalysts

Abstract High-resolution luminescence spectroscopy has been used to study the site symmetry of Eu(III) ions in Eu 2 O 3 prepared under conditions suitable for catalytic use. It was found that the Eu(III) site symmetry was a sensitive function of the pretreatment procedure, and it proved possible to determine the number of spectroscopically nonequivalent Eu(III) ions in the oxide material from an analysis of the fine structure within the emission bands. The site symmetry is altered primarily by thermal effects, and hydration of the oxide is not found to induce large changes in site symmetry.

Solution chemistry of lanthanide complexes—III: Spectroscopic studies of lanthanide complexes of glycine and polyglycines

Abstract The lanthanide complexes of glycine, diglycine and triglycine have been studied by a variety of physical means. Measurements of differential absorption of Ho(III) complexes, luminescence intensities of Tb(III) complexes, and intermolecular energy transfer from Tb(III) to Eu(III) complexes were all used to characterize the nature of the solution chemistry. The complexes tend to remain mononuclear at low pH, but associate through hydroxide linkages above neutral pH. The degree of association is much less for complexes of diglycine relative to those of glycine, suggesting that the steric nature of the amino acid ligand plays a dominant role in determining the degree of association.

Induced optical activity in the Tb(III) complex of pyridine-2,6-dicarboxylic acid through outer-sphere coordination with L-ascorbic acid

Abstract Pfeiffer effect optical activity has been induced in Tb(DPA)3−3 (DPA = pyridine-2,6-dicarboxylate) through an outer-sphere complexation with L-ascorbic acid. The optical activity was found to be essentially pH independent, and is thought to be a consequence of a perturbation upon diasteromer interconversion of the D- and L-forms of the Tb(DPA)3−3 complex that had been induced by the L-ascorbic acid. It was found that the Tb(III) emission could be quenched by the oxidized form of the ascorbic acid, and that this quenching became more efficient as the solution pH was raised. This work represents the first measurement of a Pfeiffer effect for a lanthanide complex where the optical activity was induced by an outer-sphere coordination with a chiral resolving agent.

FTIR and high-resolution photoluminescence studies of the thermal decomposition of crystalline europium hydroxide

Abstract The thermal decomposition of crystalline europium hydroxide has been studied by dynamic (differential thermal analysis and thermogravimetry) and static (fourier transform infrared and high-resolution photoluminescence spectroscopies) methods. It was deduced that crystalline europium hydroxide was thermally stable up to 200 °C, and at 250 °C decomposed to europium hydroxide (existing in the monoclinic crystal form). The oxyhydroxide was thermally stable between 300 and 350 °C, but between 400 and 450 °C decomposed to europium sesquioxide. This phase of the oxide (denoted as the C-phase) was stable between 500 and 900 ° C, but above this temperature evidence was obtained from the luminescence data that conversion to the B-phase was possible.

Solution chemistry of lanthanide complexes.5. Circularly polarized luminescence studies on Tb(III) mixed-ligand complexes containing L-aspartic acid

Abstract The complexation of L-aspartic acid by a series of mixed-ligand Tb(III) complexes has been studied by means of circularly polarized luminescence (CPL) spectroscopy. In several Tb(TDL) 2 (ASP) and Tb(MDL)(ASP) complexes (TDL = terdentate ligand, and MDL = multidentate ligand), it was established that the L-ASP ligand bound in a bidentate manner between the two carboxyl groups. However, the resulting CPL spectra were found to be vastly different in the two series of compounds, an effect whose origin probably lies in different ASP conformations in the mixed-ligand complexes. A systematic variation of the concentration of L-ASP enabled calculation of the formation constants associated with binding of this ligand by Tb(TDL) − 2 and Tb(MDL) − . The bindings of L-ASP by the Tb(MDL) series is more facile than that of the Tb(TDL) 2 series, but in all cases the formation constants are greatly reduced from the analogous value known for Tb(ASP).

Circularly polarized luminescence studies of the adducts formed between Tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III) and chiral amino alcohols

Abstract The adduct formation between the title compound and five chiral amino alcohols was studied using circularly polarized luminescence (CPL) spectroscopy. In addition, association constants for the 1:1 adducts were calculated from emission titrations. The adducts were all found to contain the amino alcohol bound to the metal ion in a bidentate manner, resulting in eight-fold coordination of the Eu(III) ion. The signs of the CPL in the various emission bands could be correlated with the absolute configuration of the chiral substrate, and the CPL is postulated to arise from a combination of chiral vicinal and conformational effects. The CPL spectra contained evidence indicating that effective axial symmetry is not present in the adducts.

Intermolecular energy transfer between lanthanide complexes—7: Study of the possible self-association between 1 : 1 complexes of lanthanides and pyridine-2,6-dicarboxylic acid

Abstract The nature of the complexes existing at low pH between lanthanide ions and pyridine-2,6-dicarboxylic acid (DPA) was investigated to learn about the possible polymeric nature of the insoluble Ln(DPA) complex formed above pH 6.5. Studies of energy transfer from Tb(DPA) to Eu(DPA) over the pH region of 2.5–6.5 were consistant with pure collisional energy transfer only, so it was concluded that the insoluble material must be monomeric in nature. Analysis of this precipitate reveals a general formula of Na 2 Tb(DPA)(OH) 5 .