Red emitting Sm(II) phosphors: thermally switchable luminescence in Sm(AlX4)2 (X = Cl, Br) by 5d-4f and intra-4f transitions.

Divalent samarium compounds of the constitution Sm(AlX4)2, X = Cl, Br, show remarkable luminescence of Sm2+. At room temperature, the luminescence is dominated by parity-allowed broad-band 4f55d1 → 4f6 emission with additional 5D0 → 7FJ narrow-line emission. At 79 K, only the intra-4f-emission is observed, rendering the mechanism thermally switchable. The luminescence processes and their temperature dependence were determined including lifetime investigations for both, room temperature and 79 K, as well as quantum efficiency determinations. In addition, a new pathway for the synthesis of Sm(AlCl4)2 and the previously unknown Sm(AlBr4)2 is reported.

Luminescent coordination polymers for the VIS and NIR range constituting LnCl3 and 1,2-bis(4-pyridyl)ethane.

A series of 14 lanthanide containing coordination polymers LnCl3 with 1,2-bis(4-pyridyl)ethane (bpe) was synthesized from either thiazole or pyridine. Depending on the ligand content, a structural diversity from 3D-frameworks [LnCl3(bpe)2]·thz, Ln = Ce-Lu, to 1D-strands [La2Cl6(bpe)2(thz)6] and [LnCl3(bpe)(py)2]·(bpe/py), Ln = Gd, Er, was obtained and characterized by X-ray single crystal diffraction, powder diffraction, differential thermal analysis and thermogravimetry (DTA/TG), IR-spectroscopy and photoluminescence spectroscopy. The compounds exhibit a variety of luminescence properties and different phenomena. This includes ligand centred fluorescence, metal-centred 5d-4f/4f-4f emission in the visible and the NIR range, antenna effects via Dexter and Förster energy transfer mechanisms, excitation dependent emission with a correlating shift of the chromaticity coordinates and inner filter effects by combined re-absorption/emission.

Mechanochemical surface functionalisation of superparamagnetic microparticles with in situ formed crystalline metal-complexes: a fast novel core-shell particle formation method.

An innovative mechanochemical method is reported for the in situ formation of crystalline metal-complexes on the surface of superparamagnetic nanocomposite microparticles. The process is demonstrated for coating Fe3O4 multicore-silica matrix particles with the 1,2,4-1H-triazole complex [ZnCl2(TzH)2]. The use of mechanochemistry demonstrates a flexible process to obtain functional shells on magnetic particle cores without the need for complicated surface-functionalisation reactions in solution. Simple mixing of the desired shell-precursors ZnCl2 and 1,2,4-1H-triazole (TzH) with the magnetic particles in a ball mill is sufficient to tailor the particle surfaces with novel functionalities while retaining the superparamagnetic behaviour.

A blue luminescent MOF as a rapid turn-off/turn-on detector for H2O, O2 and CH2Cl2, MeCN: ∞³[Ce(Im)3ImH]·ImH.

The blue emitting luminescent MOF ∞³[Ce(Im)3ImH]·ImH forms a 3D-framework with Kagomé net topology. The framework exhibits an intense blue luminescence which can be retained upon activation of the MOF with the formula ∞³[Ce(Im)3ImH]. The luminescence is metal-based due to parity-allowed 5d-4f-transitions. Time-dependent investigations of the interaction with liquid and gas analytes show that the MOF ­ by utilising 5d-4f-transitions of Ce(3+) ­ can be used as a high-speed "turn-off" detector for water and oxygen in dry air. Other protic or polar solvents, like methanol, acetone or pyridine, which also show a "turn-off"-effect can be distinguished from water-detection either on a time scale (ranging up to 250,000 : 1) or a shift of the chromaticity, the latter being pronounced for MeOH. The fast time-dependent decrease of the luminescence intensity for water arises from an extremely fast hydrolysis and is irreversible. Polar aprotic molecules like dichloromethane and acetonitrile can also result in a "turn-on"-effect of the luminescence intensity due to their behaviour as additional sensitizers for Ce(3+)-emission. We conclude that the cerium-MOF can be utilised in gas and liquid sensing applications as a detector material for water and oxygen in dry air. The luminescence is intense with good quantum yield between 55% (as-synthesised) and 36% (activated). This implies that only milligram amounts of the material are needed to detect the analyte species and is especially useful, as the MOF can be directly used as-synthesised for water detection in applications for which an irreversible signal change is desired, e.g. preventing a signal change upon unwanted re-drying.

Tuning of the dimensional linkage from the complex to the framework by thermal conversion in the system Fe/Cl/piperazine.

An attempt to control the three structural features linkage, structural dimensionality and coordination mode is presented for the combination of Fe(II) and Fe(III) chlorides together with the ditopic ligand piperazine (pipz). Thermal conversion of small units like complexes into highly aggregated structures such as coordination polymers is demonstrated for the framework formation of ∞³[Fe(II)Cl2(pipz)] starting from both FeCl2 and FeCl3. Depending on the oxidation state of iron, different reaction paths and metastable products are observed. Iron(II)chloride reacts with piperazine to form the previously unknown 2-dimensional network, ∞²[Fe(II)2Cl4(pipz)3]·pipz, which can be thermally converted into the 3-dimensional framework at elevated temperatures by release of piperazine. The use of iron(III)chloride starts with an internal redox reaction giving the divalent complex [Fe(II)Cl3(Hpipz)(pipz)] in the first step, followed by thermal conversion yielding the framework ∞³[Fe(II)Cl2(pipz)] and the salt [Fe(II)Cl3(Hpipz)(pipz)](Hpipz)Cl2. Both thermal conversion mechanisms were further investigated by in situ IR-spectroscopy, differential thermal analysis and thermogravimetry.

Lanthanide based tuning of luminescence in MOFs and dense frameworks--from mono- and multimetal systems to sensors and films.

This feature article focuses on tuning options of photoluminescence properties of lanthanide containing Metal-Organic Frameworks (MOFs) and Dense Frameworks by selection of an appropriate set of metal ions together with suitable ligands. In addition to lanthanide-only systems, frameworks with main group and transition metal ions that are heterometallic or co-doped with variable lanthanide content offer excellent tuning options for luminescence. The MOF feature porosity enables further applications such as sensors for a large number of chemical analytes by selective influences on the luminescence upon contact. The application of functional thin films marks the most recent development of this amazingly growing field, involving processing and structuring.