Joanna Cybińska

Lanthanide coordination polymers with tetrafluoroterephthalate as a bridging ligand: thermal and optical properties.

By slow diffusion of triethylamine into a solution of 2,3,5,6-tetrafluoroterephthalic acid (H2tfBDC) and the respective lanthanide salt in EtOH/DMF single crystals of seven nonporous coordination polymers, (∞)(2)[Ln(tfBDC)(NO(3))(DMF)(2)]·DMF (Ln(3+) = Ce, Pr, Nd, Sm, Dy, Er, Yb; C2/c, Z = 8) have been obtained. In the crystal structures, two-dimensional square grids are found, which are composed of binuclear lanthanide nodes connected by tfBDC(2-) as a linking ligand. The coordination sphere of each lanthanide cation is completed by a nitrate anion and two DMF molecules (CN = 9). This crystal structure is unprecedented in the crystal chemistry of coordination polymers based on nonfluorinated terephthalate (BDC(2-)) as a bridging ligand; as for tfBDC(2-), a nonplanar conformation of the ligand is energetically more favorable, whereas for BDC(2-), a planar conformation is preferred. Differential thermal analysis/thermogravimetric analysis (DTA/TGA) investigations reveal that the noncoordinating DMF molecule is released first at temperatures of 100-200 °C. Subsequent endothermal weight losses correspond to the release of the coordinating DMF molecules. Between 350 and 400 °C, a strong exothermal weight loss is found, which is probably due to a decomposition of the tfBDC(2-) ligand. The residues could not be identified. The emission spectra of the (∞)(2)[Ln(tfBDC)(NO(3))(DMF)(2)]·DMF compounds reveal intense emission in the visible region of light for Pr, Sm, and Dy with colors from orange, orange-red, to warm white.

Structure, photophysics and magnetism of a europium mixed complex, Eu(HFAA)3bipy.H2O, in the solid state and solution

Abstract Lanthanide β-diketones were used recently in organic-layered electroluminescence diodes and can also find other optical applications. An important characteristic of these materials can be correlated with donor–acceptor properties of the substituents in ligands. Single crystals of C 35 H 21 EuF 18 N 4 O 7 were obtained. The X-ray diffraction analysis shows the triclinic system and space group P 1 . The europium ion is coordinated by six oxygen atoms of hexafluoroacetylacetone and two nitrogen atoms of the 2,2′-dipyridine molecule. The coordination number of Eu(III) is completed to nine by one water molecule. Besides, one non-coordinated 2,2′-dipyridine is located in the crystal lattice which is disordered over two positions. Absorption, emission and emission excitation spectra at 293, 77 and 4 K, as well as luminescence decay time measurements are used to characterize the title compound in the solid state and in solution. The emission properties are strongly dependent on the energy of the excitation beam and on temperature. Magnetic susceptibility measurements were carried out down to 1.7 K. Correlation of the spectra and magnetic properties with details of the structure of C 35 H 21 EuF 18 N 4 O 7 was studied. These results are compared with previously reported data for related systems.

Charge compensation in RE3+ (RE = Eu, Gd) and M+ (M = Li, Na, K) co-doped alkaline earth nanofluorides obtained by microwave reaction with reactive ionic liquids leading to improved optical properties

Alkaline earth fluorides are extraordinarily promising host matrices for phosphor materials with regard to rare earth doping. In particular, quantum cutting materials, which might considerably enhance the efficiency of mercury-free fluorescent lamps or SC solar cells, are often based on rare earth containing crystalline fluorides such as NaGdF4, GdF3 or LaF3. Substituting most of the precious rare earth ions and simultaneously retaining the efficiency of the phosphor is a major goal. Alkaline earth fluoride nanoparticles doped with trivalent lanthanide ions (which are required for the quantum cutting phenomenon) were prepared via a microwave assisted method in ionic liquids. As doping trivalent ions into a host with divalent cations requires charge compensation, this effect was thoroughly studied by powder X-ray and electron diffraction, luminescence spectroscopy and 23Na, 139La and 19F solid state NMR spectroscopy. Monovalent alkali ions were codoped with the trivalent lanthanide ions to relieve stress and achieve a better crystallinity and higher quantum cutting abilities of the prepared material. 19F-magic angle spinning (MAS)-NMR-spectra, assisted by 19F{23Na} rotational echo double resonance (REDOR) studies, reveal distinct local fluoride environments, the populations of which are discussed in relation to spatial distribution and clustering models. In the co-doped samples, fluoride species having both Na+ and La3+ ions within their coordination sphere can be identified and quantified. This interplay of mono- and trivalent ions in the CaF2 lattice appears to be an efficient charge compensation mechanism that allows for improved performance characteristics of such co-doped phosphor materials.

Highly Luminescent and Color-Tunable Salicylate Ionic Liquids

High quantum yields of up to 40.5% can be achieved in salicylate-bearing ionic liquids. A range of these ionic liquids have been synthesized and their photoluminescent properties studied in detail. The differences noted can be related back to the structure of the ionic liquid cation and possible interionic interactions. It is found that shifts of emission, particularly in the pyridinium-based ionic liquids, can be related to cation-anion pairing interactions. Facile and controlled emission color mixing is demonstrated through combining different ILs, with emission colors ranging from blue to yellow.

Yttrium(III) oxomolybdates(VI) as potential host materials for luminescence applications: an investigation of Eu3+-doped Y2[MoO4]3 and Y2[MoO4]2[Mo2O7]

Two ternary yttrium(III) oxomolybdates(VI) are investigated, both structurally and spectroscopically. The crystal structure of Y2[MoO4]3 was solved at room temperature in the orthorhombic space group Pba2 (a = 1030.21(3), b = 1032.41(3), c = 1057.25(3) pm, Z = 4). In the unit cell, three discrete ortho-oxomolybdate(VI) units [MoO4]2− and two Y3+ cations, both with CN = 7 featuring a monocapped trigonal-prismatic oxygen environment, can be distinguished. Y2[MoO4]2[Mo2O7] crystallizes monoclinically in the space group P21/c (a = 681.85(2), b = 959.13(3), c = 1052.99(3) pm, β = 105.586(2)°) with two formula units per unit cell. In this compound the anionic environment of the crystallographically unique Y3+ cations also comprises seven oxygen atoms forming a monocapped trigonal prism. Furthermore, the crystal structure features both tetrahedral [MoO4]2− and pyroanionic [Mo2O7]4− entities, the latter in staggered conformation, with the bridging oxygen atom between the two vertex-shared [MoO4]2− tetrahedra residing on an inversion centre. Besides self-activated emission, resulting from the oxomolybdate(VI) units (maximum at around 600 nm), both compounds have the potential to be used as luminescence host materials, shown by spectroscopic studies involving Eu3+ as a sensitive probe. The emission spectra of Y2[MoO4]3:Eu3+ and Y2[MoO4]2[Mo2O7]:Eu3+ are dominated by the Eu3+-typical 5D0 → 7F2 transition at 614 nm. In the excitation spectra, aside from 4f-interconfigurational Eu3+ transitions at lower energies, broad charge-transfer (CT) bands due to O2− → Eu3+ or O2− → Mo6+ transitions dominate at higher energies. Comparing the diffuse reflectance spectra (DRS) of the undoped with the Eu3+-doped materials, the O2− → Mo6+ LMCT process proves to be crucial for the position of the broad CT band in the excitation spectra of both yttrium oxomolybdates(VI).

Phosphate protected fluoride nano-phosphors

A fast and easy 2-in-1 step microwave reaction procedure to phosphate coated nanofluorides allows for the formation of phosphate protected fluoride nanoparticles from simple lanthanide precursors in ionic liquids. The phosphate shell efficiently prevents the fluoride particle from decomposition in an atmosphere (containing oxygen and water) at elevated temperatures.

Reaching quantum yields ≫100% in nanomaterials

For the first time, it has been realized that trigonal GdF3:Eu, which is usually only accessible at high temperatures and very high pressures, has a superior capability as a host material for quantum-cutting materials compared to orthorhombic phase GdF3:Eu. Synthesis of these materials from ionic liquids does not only allow us to obtain oxygen-free, nanoscale fluorides – a prerequisite for fluoride quantum cutters, but by changing the ionic liquid it becomes also possible to tune the phase of the nanoparticles and thus, most importantly, the quantum cutting efficiency of the final material.

Spectroscopic and magnetic studies of the ternary praseodymium chloride K2PrCl5

The optical and magnetic properties of K 2 PrCl 5 were investigated in the 1.7-293 K temperature range and are discussed on the basis of the X-ray crystal structure data. High-resolution absorption, emission, and excitation spectra as well as decay time measurements at 293, 77, and 4 K are presented and used to characterize the excited state photophysics of K 2 PrCl 5 . Magnetic susceptibility measurements were carried out down to 1.7 K in both the low and high field regime. Changes in the magnetic moment with temperature are discussed on the basis of the structural data. Spectroscopy and magnetism of K 2 PrCl 5 are related to respective results of other polynuclear and heteronuclear polymeric systems and are correlated with their EPR data.

Octulene: A Hyperbolic Molecular Belt that Binds Chloride Anions

Octulene, the higher homologue of kekulene and septulene, was synthesized using the fold-in method. This new hydrocarbon macrocycle contains a large 24-membered inner circuit, which is peripherally fused to 24 benzene rings. Such an arrangement produces considerable hyperbolic distortion of the π-conjugated surface. The consequences of distortion in octulene were explored using photophysical methods, which revealed a reduced electronic band gap and greater flexibility of the π system. Octulene contains a functional cavity with a diameter larger than 5.5 Å that is capable of efficiently binding the chloride anion in a nonpolar solvent (Ka = 2.2(4)×104  m-1 , 1 % dichloromethane (DCM) in benzene). The octulene-chloride interaction is stabilized by eight weak C(sp2 )H⋅⋅⋅Cl bonds, providing the first example of a hydrocarbon-based anion receptor.

An Electron-Deficient Azacoronene Obtained by Radial π Extension.

A hexapyrrolohexaazacoronene derivative containing 37 fused rings, the largest such system to date, was obtained from a naphthalenomonoimide-pyrrole hybrid in a concise and efficient synthesis. This large heterocycle is electron-deficient and shows extended redox activity, spanning at least 13 oxidation levels, but is otherwise chemically stable. Radial expansion of the π system creates a chromophore characterized by strong fluorescence and solvatochromism in the neutral state, and strong near-infrared absorption in the charged states. Additionally, the enlarged and ruffled aromatic surface supports a unique self-assembly mode in the crystal, leading to the formation of highly solvated organic clathrates.