Search

The structural parameters of the rare-earth diacetate halide trihydrates, RE(OAc)2Hal·3H2O with RE = Ce − (Pm) − Lu and Hal = Cl, Br, have been determined by low temperature, high-resolution SCXRD in order to examine the effect of lanthanide contraction on the coordination geometry in this series of isomorphous compounds consisting of cationic, acetate-bridged, non-linear, one-dimensional coordination polymers of composition [RE(H2O)3(OAc)2]+ and laterally hydrogen bonded halide ions, Hal−. Although the shrinkage of the unit cell volume follows lanthanide contraction very well over the complete range of investigated RE elements, many other parameters (i.e., lattice constants, angles and distances in the RE··· RE alignment, RE-O bond lengths, etc.) exhibit a more complex response on lanthanide contraction often expressed by sigmoid curves that can be ascribed to a continuous transition from CN9 (RE = Ce) to CN8 (RE = Lu) as one acetate group loses the chelate function, an effect accompanied by significant structural changes of the carboxylate group. Therefore, data are best analyzed by use of two subsets represented by the two different structure types of Ce and Lu, the structural features of which change with decreasing/increasing the size of RE3+, up to the borderline between both subsets.

Four new rare-earth metal–organic frameworks containing thieno[3,2b]thiophene-2,5-dicarboxylate (ttdc2−) with general formulae [M2(DMF)4(ttdc)3] (M3+ = Y3+ for 1, La3+ for 2, Tb3+ for 3) and [M2(H2O)2(ttdc)3] (M3+ = Lu3+ for 4) were synthesized. Their crystal structures were determined by performing a single-crystal X-ray diffraction analysis. Coordination polymers 1–3 are based on the binuclear metal-carboxylate building units with the formulae {M2(DMF)4(OOCR)6}. The six-connected blocks in 1–3 form a three-dimensional network with the primitive cubic (pcu) topology. Coordination framework 4 is based on chains comprised by stretched pseudo-binuclear metal-carboxylate building units. The chains are interconnected in four directions with ttdc2− linkers forming the 3D framework. The luminescent properties were studied for the synthesized frameworks in the solid state. All the coordination frameworks show a broad blue emission band (λex = 380 nm) typical for intra-ligand electron transitions. The sensing properties of 3 dispersions in solutions were investigated in detail and the luminescent response (quenching) was discovered in the presence of cinnamaldehyde and quinoline in diluted solutions at concentrations of as low as 4 × 10−1 vol.% and 4 × 10−2 vol.% (~3 × 10−3 M), respectively.

Hydrothermal reaction of Ln nitrate and Na2WO4 at pH=8 and 200 °C for 24 hours, in the absence of any additive, has directly produced the scheelite-type sodium lanthanide tungstate of NaLn(WO4)2 for the larger Ln3+ of Ln=La-Dy (including Y, Group I) and an unknown compound that can be transformed into NaLn(WO4)2 by calcination at the low temperature of 600 °C for the smaller Ln3+ of Ln=Ho-Lu (Group II). With the successful synthesis of NaLn(WO4)2 for the full spectrum of Ln, the effects of lanthanide contraction on the structural features, crystal morphology, and IR responses of the compounds were clarified. The temperature- and time-course phase/morphology evolutions and the phase conversion upon calcination were thoroughly studied for the Group I and Group II compounds with Ln=La and Lu for example, respectively. Unknown intermediates were characterized by elemental analysis, IR absorption, thermogravimetry, and differential scanning calorimetry to better understand their chemical composition and coordination. The photoluminescence properties of NaEu(WO4)2 and NaTb(WO4)2, including excitation, emission, fluorescence decay, and quantum efficiency of luminescence, were also comparatively studied for the as-synthesized and calcination products.

The existing range of the centrosymmetric, triclinic RE(OAc)3 · 2AcOH structure type has been extended for RE = Eu and Gd while the structure data of the Nd- and Sm-compounds have been revised and corrected, respectively, using low temperature (T = 100 K), well resolved (2θmax = 56°), highly redundant SCXRD data in order to evaluate the structural evolution within this class of acetic acid solvates by statistical methods. Within the nine-fold mono-capped square-antiprismatic coordination spheres of the RE3+ ions, RE-O distances decrease as a result of lanthanide contraction; some with different rates depending on the coordination modes (2.11/2.21) of the acetate ions. The experimental data show that the internal structural parameters of the acetate ions also correlate with their coordination modes. Both acetic acid molecules act as hydrogen bond donors but only one as monodentate ligand. The geometries of the hydrogen bonds reveal that they are strongly influenced by the size of the rare earth atom. The non-linear, one-dimensional coordination polymer propagates with unequal RE···RE distances along the a-axis. Rods of the coordination polymer are arranged in layers congruently stacked above each other with the hydrogen bonded acetic acid molecules as filler in between. In most cases, data fitting is best described in terms of a quadratic rather than a linear regression analysis.