Grażyna Oczko

X-Ray analysis and excited state dynamics in a new class of lanthanide mixed chelates of the type LnPhβ3·Phen (Ln=Sm, Eu, Gd, Tb)

A new type of lanthanide complex with a derivative of β-diketone and phenanthroline, LnPhβ3·Phen [where Phβ = CCl3–C(O)–N–P(O)–(OCH3)2; Phen = 1,10-phenanthroline, Ln = Sm, Eu, Gd, Tb] was synthesised. The X-ray diffraction analysis of the Sm(III) complex shows that it is in the monoclinic system and P21/c space group. There are two different Sm3+ ions with insignificant differences between the Sm–O, –N distances (0.005 A) and a CN = 8. Absorption, emission and emission excitation spectra at 293, 77 and 4.2 K were used to characterise the title compounds in the solid state and in solution. The luminescence spectra at 77 K for the Eu analogue are complex and two components in the 5D0 → 7F0 transition show that Eu3+ ions reside in two symmetry sites. The spectroscopic results correspond well to the crystal structure of the SmPhβ3·Phen compound and confirm that the Sm3+, Eu3+ and Tb3+ monocrystals are isostructural. Efficient energy transfer sensitises the interion emission from 5D4 or 5D0 levels of Tb(III) and Eu(III) after ligand band excitation. Based on the splitting of the levels observed at 4.2 K in the single crystal spectra of Tb and Eu, as well as the absorption, phosphorescence and excitation spectra, energy level diagrams are proposed. The mechanism of energy transfer and excited state dynamics are discussed. Strong vibronic coupling was observed mainly in the 7F0 → 5D2 electronic transition. The IR spectra were used to analyse the vibronic components. Analysis of the emission spectra of a Eu3+-doped silica sol-gel sample was made and compared to those for the title monocrystals. The total spectral characteristics of the materials permits an evaluation of their potential applicability.

Correlation between spectroscopic characteristics and structure of lanthanide phosphoro-azo derivatives of β-diketones

Two types of lanthanide (Nd, Eu, Pr) compounds of formulae: Ln(HX) 3 Cl 3 (1), Ln(HX) 3 (NO 3 ) 3 (2) [where HX=CCl 3 CO-NH-PO(NEt 2 ) 2 ] with the same ligand type but with different coordination numbers (as a consequence of different site symmetries) were obtained. X-ray data indicate the formation of octahedral complexes of (1), strongly distorted into trigonal symmetry, the strongest distortion observed for europium single crystals. On the other hand, the second type of crystals creates intermediate coordination polyhedra with low symmetry; anisotropy of intensities of 4 I 9/2 → 4 G 5/2 , 2 G 7/2 transition of Nd crystal well confirms the above structure. High resolution absorption spectra of single crystals of the title compounds were recorded at different temperatures from 293 to 4.2 K. Splitting of levels was determined. Intensities of f-f transitions were calculated and changes of their oscillator strengths, in the region of hypersensitive transitions, for the series Pr, Nd, Eu crystals were related to stronger distortion of the symmetry with a decrease of the ionic radius. Oscillator strength values and Judd-Ofelt parameters were calculated and compared to the respective data reported earlier. Analysis of the electronic components in low temperature spectra point on the D 3 site in (1) and most probably C 2v in (2). Electron-phonon coupling was observed in low temperature spectra and its probabilities was analysed for two types of compounds with different symmetries. Vibronic components were related to the internal ligand modes and to the localised Ln-L x modes.

Spectroscopy studies of lanthanide trichloroacetate single crystals

Abstract The single crystals of some lanthanide carboxylates are characterized by a lack of inversion symmetry, so they could be used for generation of the second harmonic.1−5 Single crystals of neodymium and erbium trichloroacetate were synthesized and shown to form the polymeric chain linking dimeric subunits, where the lanthanide ions can occupy different site symmetry positions. The absorption and luminescence spectra of single crystals of the title compounds were measured at room and liquid helium temperatures; Stark components were determined and analysed in terms of interacting ions. Spectroscopic properties were related to the X-ray crystal data. Probabilities of f-f transitions depending on the orientation of biaxial single crystals were considered.

Polymeric polynuclear systems of Pr, Yb and Pr:Cu trichloroacetates; their spectroscopy and magnetism

Abstract Heteronuclear copper–lanthanide compounds are the subject of the studies for the reason of their unusual structure features, optical, magnetic, catalytic properties and because of their potential application in superconducting ceramics. Synthesis, spectroscopic and magnetic characterisation of polymeric one-dimensional lanthanide (Pr, Yb) trichloroacetates (I, II) and heteronuclear CuPr 2 (Cl 3 CCOO) 8 ·6H 2 O (III) single crystals were undertaken. Structures of I, II are isomorphic with erbium trichloroacetate and that of III with respective neodymium compound. In the structure of III the polymeric chain is built of dimers of two crystallographically independent types of PrO 8/9 polyhedra linked by carboxyl bridges. These dimers are separated by square planar coordinated cooper ions bridged to the lanthanide by four carboxyl groups and two water molecules. High resolution spectra down to 4 K were investigated and cooperative effects were analysed. Magnetic susceptibility measurements in the range 300–1.8 K were carried out. Optical and magnetic properties are discussed on the basis of X-ray data. Electron transition probabilities were calculated and cooperative interaction of ion-pairs coupled in polymeric chain was considered. Vibronic components were observed and assigned on the basis of Raman data.

Crystal structure, magnetism and photophysics of the lanthanide maleates RE(C4O4H3)3·8H2O (RE=Nd, Sm)

This article reports the results of an X-ray study, of the magnetic and spectroscopic characteristics of lanthanide maleates. An X-ray single crystal structure determination was performed for Nd(C 4 O 4 H 3 ) 3 .8H 2 O. The crystal structure is triclinic (PI, Z = 2, a = 7.285(1) A, b=10.394(2) A, c=16.765(3) A, α=72.13(2)°, β = 87.77(2)°, γ = 70.86(2)°, R all = 0.0322) and isotypic with the respective praseodymium compound. Nd 3+ is nine-fold coordinated by oxygen atoms in the form of a tricapped trigonal prism. Two carboxyl groups of two crystallographically independent hydrogenmaleate ions are attached to Nd 3+ in a monodentate manner. The third hydrogenmaleate anion forms hydrogen bonding with unbound and coordinated water molecules. Thus, the crystal structure of the title complexes points to an unusual carboxyl group coordination with lanthanide ions. Absorption spectra of neodymium and samarium single crystals at 293 and 4.2 K were recorded. Analysis of the f-f transition probabilities were performed and Judd-Ofelt parameters were determined. Strong vibronic coupling was found, mainly promoted by modes which correspond to co-ordinated moieties of ligand molecules. A structural transformation is expected based on the relatively high temperature factors in the X-ray data. This was confirmed by the spectroscopic investigation. Magnetic susceptibility results were correlated with X-ray data and results reported previously.

Spectroscopic studies of neodymium and erbium fluoroacetate single crystals

Abstract The spectroscopic (UV/VIS, IR) results of Ln(H x F 3− x CCOO) 3 ·3H 2 O (Ln=Nd, Er; x =0,1) compounds are presented in this paper. Electronic absorption spectra of these single crystals were measured at room and low temperatures. Intensities of f–f transitions were analysed on the basis of Judd–Ofelt theory. The effects of different structures on the spectroscopic properties of the systems under investigation were considered. The results for the single crystals of the title compounds were compared to those for the lanthanide trichloroacetate monocrystals. Vibronic mechanism of the 4f–4f transitions was discussed, and covalent effect in the spectra was considered.

Crystal structure and absorption spectroscopy of Ln(HF 2 CCOO) 3 ·3H 2 O (Ln=Pr, Er) single crystals

Abstract Crystal structures of Ln(HF2CCOO)3·3H2O (Ln=Pr, Er) compounds were determined by X-ray analysis. Both crystals proved to be isomorphous. They are triclinic, space group P 1 , with a=8.394(2) A , b=9.509(2) A , c=9.623(2) A , α=66.60(2)°, β=79.34(2)°, γ=77.74(2)° and Z=2 for the Pr compound and a=8.258(2) A , b=9.358(2) A , c=9.458(2) A , α=66.90(2)°, β=79.34(2)°, γ=77.80(2)° and Z=2 for the Er one. The Ln(III) ion adopts an 8-coordinate geometry with six oxygen atoms from carboxylate groups and two oxygen atoms from water molecules, which is best described as the best slightly deformed square antiprism. Absorption spectra of the Pr(HF2CCOO)3·3H2O single crystal were measured at room and low temperatures. Intensities of the f–f transitions were analysed on the basis of the Judd–Ofelt theory. The results for the praseodymium difluoroacetate single crystals are compared to those for the lanthanide trifluoroacetates monocrystals. Vibronic mechanism of 4f–4f transitions is discussed.

Spectroscopic properties of neodymium monochloroacetate single crystal as an example of complex containing Nd(III) in three different symmetry sites

Abstract The neodymium monochloroacetate complex was obtained in the form of monocrystal. The absorption and emission spectra for this single crystal were recorded at room and low temperatures down to 4.2 K. Intensities of electronic lines and Judd–Ofelt parameters were calculated. Splitting and energies of electronic levels were considered and compared to those for the neodymium trichloroacetate single crystals. The covalent effect in the spectra was discussed. The results obtained from the low temperature spectra for [{Nd(ClH 2 CCOO) 3 } 3 (H 2 O) 5 ] n indicated three different symmetry sites of Nd 3+ ion. Correlation with the X-ray data was made.

Absorption and emission of europium trichloroacetate single crystal at room and low temperatures

Abstract Single crystals of the title compound were synthesized; their absorption spectra and luminescence spectra were measured at 293 K, 77 K and 5 K. The intensity analysis was made and the temperature dependence of intensity was discussed. Stark components were determined and the ion pair interaction was considered. The spectroscopic results were related to our previous data.

Synthesis and spectroscopic characteristics of a new class of lanthanide compounds of formulae Ln(HX)3(NO3)3 and Ln(HX)3Cl3

Two series of the lanthanide (Eu, Pr) compounds of the formulae Ln(HX)3Cl3 (1); Ln(HX)3(NO3)3 (2) [where HX=CCl3CO–NH–PO(NEt2)2] with C.N.=6 and 9 were obtained in the form of monocrystals. The spectroscopic properties of these compounds were investigated at 293, 77 and 4.2 K and the results related to their structures. Correlation was made with the spectroscopic data and structure of the Eu and Nd respective chelates. Essential differences were found in coordination mode of ligand molecules in those systems. Intensity analysis of electronic transitions, electron–phonon coupling, as well as splitting and energies of electronic levels were used as tests of metal bonding in the systems under investigation. The electronic f–f transitions of praseodymium (1, 2) compounds show drastic differences in oscillator strength values, pointing thus at substantial differences in symmetry of the metal centre. Judd–Ofelt parameters were calculated with low errors of estimation. The relatively strong vibronic lines appear at displacement frequencies, corresponding to both ligand and Ln–Ln localised vibrational modes.