Alkaline earth imidazolate coordination polymers by solvent free melt synthesis as potential host lattices for rare earth photoluminescence: (x)(∞)[AE(Im)2(ImH)(2-3)], Mg, Ca, Sr, Ba, x = 1-2.
ABSTRACT The series of alkaline earth elements magnesium, calcium, strontium and barium yields single crystalline imidazolate coordination polymers by reactions of the metals with a melt of 1H-imidazole: (1)(∞)[Mg(Im)(2)(ImH)(3)] (1), (2)(∞)[AE(Im)(2)(ImH)(2)], AE = Ca (2), Sr (3), and (1)(∞)[Ba(Im)(2)(ImH)(2)] (4). No additional solvents were used for the reactions. Co-doping experiments by addition of the rare earth elements cerium, europium and terbium were carried out. They indicate (2)(∞)[Sr(Im)(2)(ImH)(2)] as a possible host lattice for cerium(III) photoluminescence showing a blue emission and thus a novel blue emitting hybrid material phosphor 3:Ce(3+). Co-doping with europium and terbium is also possible but resulted in formation of (3)(∞)[Sr(Im)(2)]:Ln, Ln = Eu and Tb (5), with both exhibiting green emission of either Eu(2+) or Tb(3+). The other alkaline earth elements do not show acceptance of the rare earth ions investigated and a different structural chemistry. For magnesium and barium one-dimensional strand structures are observed whereas calcium and strontium give two-dimensional network structures. Combined with an increase of the ionic radii of AE(2+) the coordinative demand is also increasing from Mg(2+) to Ba(2+), reflected by four different crystal structures for the four elements Mg, Ca, Sr, Ba in 1-4. Different linkages of the imidazolate ligands result in a change from complete σ-N coordination in 1 to additional η(5)-π coordination in 4. The success of co-doping with different lanthanide ions is based on a match in the chemical behaviour and cationic radii. The use of strontium for host lattices with imidazole is a rare example in coordination chemistry of co-doping with small amounts of luminescence centers and successfully reduces the amount of high price rare earth elements in hybrid materials while maintaining the properties. All compounds are examples of pure N-coordinated coordination polymers of the alkaline earth metals and were identified by single crystal X-ray analysis and powder diffraction. The degree of co-doping was determined by SEM/EDX. Mid IR, Far IR and Raman spectroscopy and micro analyses as well as simultaneous DTA/TG were also carried out to characterize the products in addition to the photoluminescence studies of the co-doped samples.
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ABSTRACT: The 2D-coordination polymer 2∞[Ce2Cl6(bipy)4]·py (bipy = 4, 4′-bipyridine) shows a 5d-4f centered emission in the soft UV-B region. It was synthesized via the reaction of anhydrous CeCl3 and 4, 4′-bipyridine in pyridine under solvothermal conditions. The two-dimensional sheet structure consisting of 4, 4′-bipyridine coordinated Ce2Cl6 dimers closes the gap between the known lanthanum 3∞[La2Cl6(bipy)5]·4bipy framework and the 2D networks of the formula 2∞[Ln2Cl6(bipy)3]·2bipy from praseodymium on. They differ in the number of coordinating bipy linkers, which decreases along La > Ce > Pr, with the remarkable observation that lanthanum, cerium, and praseodymium exhibit different network constitutions. The structure of 2∞[Ce2Cl6(bipy)4]·py exhibits a cem topology constituted of double strands, which are diagonally linked by 4, 4′-bipyridine forming trapezoid cavities in-between the strands. The cavities contain intercalated pyridine molecules.Zeitschrift für anorganische Chemie 10/2014; · 1.25 Impact Factor
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ABSTRACT: The highly luminescent framework series 3∞[Sr1−xEuxIm2], x = 0-1, was successfully grown in situ on nanostructured macroporous anodic aluminium oxide (AAO) membranes during the framework formation. Thereby, a novel in situ coating strategy for thin film creation of metal-organic frameworks (MOFs) and dense frameworks directly deriving from the metals was developed. Depending on synthesis conditions and growth duration, the luminescent materials start growing inside the AAO macropores and on the pore mouths, yielding patterned framework surfaces, before a continuous smooth MOF layer is formed. The films retain the luminescence of the corresponding bulk materials and can be grown with variable film thickness on the nanometer scale.CrystEngComm 01/2013; 15(45-45):9382-9386. · 3.86 Impact Factor
- Journal of Chemical Crystallography 09/2014; 44(9):443-449. · 0.48 Impact Factor