Anna Mondry

Optical spectroscopy and structure of neodymium complexes with 2,6-pyridine-dicarboxylic acid in solution and single crystal at room and low temperatures

Abstract X-ray characterization of a compound reported as Na3[Nd(dpa)3]·15H2O by Albertsson was repeated and it was found to be a 14-hydrate. Absorption spectra of the crystal were measured along the a axis at room temperature and at 5 K. The results for the crystal were compared with those for Nd(III) aquoion and Nd(III)-dipicolinate solutions. Intensities of the f-f transitions were analyzed according to the Judd-Ofelt theory. The good correspondence between the values of oscillator strength of the hypersensitive transition for [Nd(dpa)3]3− complex in solution and in the crystal suggests an analogy between the coordination polyhedra; however, the crystal field splitting is different, best seen for the 4 I 9 2 → 2 P 1 2 transition. The contribution of polarization and electrostatic field mechanisms to the oscillator strengths is discussed.

Optical spectroscopy of neodymium(III) complexes with diethylenetriaminepentaacetic acid in solution and in [C(NH2)3]2[Nd(dtpa)(H2O)]·7H2O single crystal

Abstract The crystal structure of [C(NH2)3]2[Nd(dtpa)(H2O)]·7H2O (H5dtpa=diethylenetriaminepentaacetic acid) has been determined. Electronic absorption spectra of a single crystal of the [C(NH2)3]2[Nd(dtpa)(H2O)]·7H2O compound were measured at room and liquid helium temperatures. In order to investigate the formation and structure of NdIII–dtpa species occurring in solution, the spectral results for the crystal were compared with those of the NdIII–dtpa (1:1) complex in solution. The analysis of spectral properties of this system may be applied for solutions of coordination chemistry problems encountered in lanthanide polyaminopolycarboxylates.

Spectroscopy and structure of neodymium complexes with EDTA

Abstract The spectral properties of Nd 3+ -EDTA solutions were investigated at different Nd 3+ and EDTA concentrations within a broad pH region. The analysis of the oscillator strength values of the ‘hypersensitive’ 2 G 7/2 , 4 G 5/2 ← 4 I 9/2 transition and of the Judd- Ofelt intensity parameters was performed in order to investigate the formation and the type of bonding in the Nd 3+ -EDTA species. The correlation of these results with NMR and kinetic data has made it possible to suggest a relatively complete model of the Nd 3+ -EDTA coordination. The X-ray data in the solid phase confirmed the proposed model.

Structure and optical spectroscopy of holmium(III) triethylenetetraaminehexaacetate in single crystal and in solution

The crystal structure of [C(NH2)3]3[Ho(ttha)]·3H2O (H6ttha=triethylenetetraaminehexaacetic acid) has been determined. The coordination environment of the HoIII ion is composed of five carboxylate oxygen atoms and four nitrogen atoms. Electronic absorption spectra of a [C(NH2)3]3[Ho(ttha)]·3H2O single crystal were measured at room and liquid helium temperatures and compared with those of the HoIII–ttha (1:1) complex in solution. The results suggest that a species of coordination geometry similar to that of the [Ho(N4O5)]3− type found in the crystal exists predominantly in solution at pH>5. At lower pH values, as for other LnIII–ttha complexes, coordination equilibria are observed.

Spectroscopy and structure of heavy lanthanide complexes with EDTA

Abstract The electronic absorption method has been used to study the equilibria and structure of Ho 3+ and Er 3+ complexes with EDTA. Spectral properties of these systems are investigated for different Ln 3+ concentrations at M:L ratios of 1:1 and 1:2 within a broad pH range. Analysis of the ‘hypersensitive’ transition band shapes and intensities and of the Judd–Ofelt intensity parameters τ λ allows us to investigate the formation and the type of bonding of Ln 3+ –EDTA species occurring in solution. Comparison of the results for Ho 3+ and Er 3+ with Nd 3+ –EDTA [1] complexes shows a significant difference between EDTA complexes of heavy and light lanthanides.

f–f Transition intensities of europium(III) acetate complexes in a single crystal and in solution

Abstract Optical absorption spectra of Eu III -acetate complexes in a single crystal and in solution as well as of the Eu III -aquoion were analyzed. With decreasing temperature from 293 to 4 K an unusually strong intensity decrease of the 7 F 0 → 5 D 2 , 7 F 0 → 5 D 1 and 7 F 0 → 5 D 0 transitions in the crystal was detected. A distinct influence of light polarization on these transitions caused by crystal anisotropy was observed. Spectral intensities of the investigated systems were parametrized in terms of the Judd–Ofelt theory.

Spectroscopy of heavy lanthanide complexes with NTA

Abstract Spectroscopic properties of Ho 3+ -NTA and Er 3+ -NTA systems were investigated for different M:L ratios and different concentrations of M within a broad pH range. Analysis of the oscillator strength values of the ‘hypersensitive’ transitions and of the Judd–Ofelt intensity parameters τ λ allowed us to investigate the formation and the type of bonding of the Ln 3+ –NTA species occurring in solution. These results are in good agreement with the results of luminescence measurements.

Spectroscopic properties of Ho3+ complexes with dipicolinic acid in solufion and single crystals

Abstract The absorption spectra of hexagonal Na 3 [Ho(dpa) 3 ]·NaClO 4 ·10H 2 O single crystals were measured in the region 300–2100 nm along the z axis at temperature fange 293–118 K. Probabilities of f-f transitions were analysed on the basis of the Judd-Ofelt theory. The single crystal results were compared to those of the Ho 3+ -dpa system in aqueous solutions for different molar ratios of Ho 3+ :dpa. The good correspondence between the spectra of [Ho(dpa) 3 ] 3− compounds in solution and in the single crystal suggests analogy between both coordination polyhedra. These results also suggest that the mechanism of the hypersensitive transition is vibronic as well.

The power and limits of the Judd—Ofelt theory: a case of Pr3+ and Tm3+ acetates and dipicolinates

Electronic absorption spectra of crystals and solutions of praseodymium and thulium acetates and dipicolinates are reported. The influence of spectral properties of both ligands on intensities of the f—f transitions in the crystals studied is discussed. In the near-IR region, overtone vibrations of ligands are strongly coupled with the f—f transitions, particularly with the hypersensitive ones. In the UV spectral range, absorption bands of the π → π*, n → π* and possible charge transfer of metal ⇔ ligand transitions affect f—f transitions and should also be taken into account. The phenomenological Judd—Ofelt parameters evaluated for praseodymium complexes in solution and crystals are meaningless, because no set of intensities unbiased by ligand transitions and/or neighbouring f-d configurations is available. For Tm3+ compounds the Judd-Ofelt analysis has given quite good results, however no significant influence of the metal ion environment changes on the Ωλ parameters can be observed.

Application of circularly polarized luminescence spectroscopy to the solution structure of racemic polyaminocarboxylate lanthanide (III) complexes

Abstract Circularly polarized luminescence from 1:1 complexes of Eu(III) with triethylenetetra-aminehexaacetic acid (TTHA) following excitation with circularly polarized light is reported. This observation is consistent with a solution structure for this complex that is chiral, and stable on the emission time scale of Eu(III) (approximately 1.2ms). Additional measurements show only a slight dependence on temperature, and an estimate for the activation energy for racemization (23 kcal/mol) may be obtained. Attempts at detecting enantio-selective quenching of Tb(TTHA)3- by optically active Ru(phen)2+3 are also reported. Although significant quenching was observed, and the time-decay of the Tb(III) emission was not mono-exponential, no enantio-selectivity was found. This latter result may be interpreted in terms of the lack of discriminating short-range diastereomeric interactions between the chiral ion pairs.