Claudia Wickleder

Surface-Anchored MOF-Based Photonic Antennae

The loading of a metal-organic framework (MOF), [Cu(3)(btc)(2)xH(2)O] HKUST-1, with europium β-diketonate complexes is studied with the goal to using the porous molecular framework as a photonic antenna. Whereas loading of HKUST-1 powder particles produced via the conventional solvothermal synthesis method was strongly hindered, for HKUST-1 SURMOFs, thin MOF films fabricated using the liquid phase epitaxy method, a high filling factor can be achieved. The optical properties of the HKUST-1-MOFs before and after loading were analysed with the aid of luminescence spectroscopy. Careful analysis of the absorption spectra reveals the presence of an effective energy transfer between the HKUST-1 framework and the Eu(3+) centers.

Diastereoselective formation of luminescent dinuclear lanthanide(III) helicates with enantiomerically puretartaric acid derived bis(β-diketonate) ligands

The chiral tartaric acid derived bis(β-diketonate) ligands 1–3-H2 diastereoselectively form dinuclear triple-stranded helicates with a series of lanthanide(III) ions (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), which bind water molecules as additional co-ligands. In the cases of europium(III) and terbium(III) ions, bright red or green luminescence is observed, respectively. Hereby the energy transfer from the ligand to the metal is most effective with the bromophenyl-substituted ligand 3-H2. Reaction of 3-H2 with europium(III) in a 4 : 2 ratio results in a highly luminescent quadruple-stranded dinuclear complex [34Eu2]2–.

Spectroscopic properties of SrZnCl4:M2+ and BaZnCl4:M2+ (M=Eu, Sm, Tm)

Abstract The emission spectra of the divalent rare-earth ions Eu 2+ , Sm 2+ and Tm 2+ , doped into the new compounds SrZnCl 4 and BaZnCl 4 , are reported. Eu 2+ and Tm 2+ show broad 4 f n −1 5 d →4 f n emission. Due to the smaller crystal-field splitting, the emission bands for BaZnCl 4 :M 2+ are shifted to higher energies when compared to SrZnCl 4 :M 2+ . For SrZnCl 4 :Sm 2+ at 298 K broad 4 f 5 5 d →4 f 6 emission is observed, while at 20 K additional lines due to the 5 D 0 → 7 F J transition appear. BaZnCl 4 :Sm 2+ shows only line spectra at low temperature. At 298 K a weak d → f transition is observed. The results are discussed and compared with the corresponding measurements of SrCl 2 and BaCl 2 doped with the divalent rare-earth ions.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu-II(Cp-BIG)(2)] (Cp-BIG=(4-nBu-C6H4)(5)-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu[superscript II](Cp[superscript BIG])[subscript 2]] (Cp[superscript BIG]=(4-nBu-C[subscript 6]H[subscript 4])[subscript 5]-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Copper(I) thiocyanate coordination polymers with dimethylpyrazine: synthesis, crystal structures, thermal and luminescence properties

Abstract The new copper(I) coordination polymers poly[(di-μ2-thiocyanato-N,S)-(μ2-2,5-dimethylpyrazine-N,N)] dicopper(I) (I) and poly[di-μ2-thiocyanato-N,S)-(μ2-2,3-dimethyl-pyrazine-N,N)] dicopper(I) (II) were prepared by the reaction of copper(I) thiocyanate with 2,3- and 2,5-dimethylpyrazine in acetonitrile. In all compounds different CuSCN sub-structures are found which are connected by the dimethylpyrazine ligands to multi-dimensional coordination networks. The thermal properties of all compounds were investigated using simultaneous differential thermoanalysis (DTA), thermogravimetry (TG) and mass spectrometry (MS) as well as temperature resolved X-ray powder diffraction. On heating, compound I and II loose all of the dimethylpyrazine ligands in an endothermic reaction and transform directly into copper(I) thiocyanate. Optical investigations show two excited states for both compounds in absorption and in luminescence measurements which are both, MC and LMCT in character.

Spectroscopic behaviour of lanthanide(III) coordination compounds with Schiff base ligands

The spectroscopic properties of lanthanide(III) complexes with Schiff base ligands (substituted salicylaldimines) are described. Optical absorption spectra of Nd(III), Ho(III) and Er(III) complexes dissolved in chloroform were recorded. The dipole strengths of the transitions were determined experimentally and parameterised in terms of three phenomenological Judd–Ofelt intensity parameters Ωλ (λ=2, 4 and 6). The complexes exhibit unusually intense hypersensitive transitions. The intensity enhancement can be attributed to the highly polarisable ligands and to the low site symmetry around the lanthanide ions (C1). The luminescence spectra of Eu(III) compounds were measured, but the emission intensities were low.

Photoluminescence of CsMI3:Eu2+ (M = Mg, Ca, and Sr) – a spectroscopic probe on structural distortions

The photoluminescence of Eu2+ ions doped in iodidoperovskites, CsMI3 (M = Mg, Ca, Sr), was studied. Eu2+ occupies the alkaline earth site in each of these compounds. The emission spectra of the doped perovskites are characterized by 4f65d1 → 4f7 transitions of Eu2+ located in the yellow range for CsMgI3 and the blue range for CsCaI3 and CsSrI3, respectively. All excitation spectra provide a well-resolved fine structure arising from different 7FJ (J = 0,…,6) levels of the 4f6 core of the excited state configuration, indicating a weak exchange interaction with the 5d electron. The decay times and temperature dependence of the luminescence were also analyzed. Both CsMgI3:Eu2+ and CsSrI3:Eu2+ show a redshifted emission with respect to CsCaI3:Eu2+. This is explained by trigonal distortions of the [EuI6]4− octahedra in the former two compounds. The energetic order of the resulting crystal field states is justified in terms of the angular overlap model of ligand field theory. This series of Eu2+ doped earth alkaline iodidoperovskites may serve as a textbook example for the detailed understanding of the structure–luminescence relationships of Eu2+ ions, which is very important for tailoring functional materials for respective applications.

Syntheses, structures and luminescence properties of novel metal–organic frameworks based on zinc(II), cadmium(II) or lead(II) and a 2,2′-dimethoxy-functionalised biphenyl linker

Three metal–organic frameworks (MOFs) based on zinc(II) (1), cadmium(II) (2) or lead(II) (3) and the functionalised biphenyl linker biphenyl-2,2′-dimethoxy-4,4′-dicarboxylate, [4,4′-(CO2)2-2,2′-(OMe)2-1,1′-(C6H3)2] (L), were synthesised. Compounds 1 and 3 exhibit different three-dimensional networks with the Zn4O(O2C)6(H2O) unit as the secondary building unit (SBU) in the Zn-based MOF [{(Zn4O)(L)3(H2O)}·4.5DMF]n (1) and Pb6O2(O2C)4 clusters as SBU in the Pb-based MOF [{(Pb6O2)L4}·2EtOH]n (3), as shown by X-ray analysis. The Cd-based MOF [{(Cd3L4)2(CdL2)}·8DMF·8Me2NH2·2Cl]n (2) exhibits two interpenetrated three-dimensional networks formed from two different types of secondary building units, Cd3(μ-O2C)6(O2C)2 and Cd(O2C)4. Compounds 1–3 are thermally stable up to 420, 360 and 380 °C, respectively (according to DTA–TG). All compounds show bluish emissions visible with the naked eye, which could be assigned to S1,2 → S0 transitions of the aromatic units by comparison with the luminescence properties of the free ligand.

ACCURATE INTERMOLECULAR BINDING ENERGIES OF 1-NAPHTHOL TO BENZENE AND CYCLOHEXANE

Accurate dissociation energies were determined for gas-phase complexes between 1-naphthol and benzene, d6-benzene and cyclohexane, using the stimulated emission pumping resonant two-photon ionization spectroscopy technique in supersonic jets. The dissociation energies obtained for the electronic ground state are surprisingly large being D0 = 5.07±0.07 kcal/mol for 1-naphthol · benzene, 5.08±0.06 kcal/mol for 1-naphthol · d6-benzene, and 6.92±0.03 kcal/mol for 1-naphthol · cyclohexane, respectively. The dissociation energies scale well with the parallel molecular polarizabilities.