Crystal structure and thermal behavior of a chromium-piperazinium phosphate

(C₄N₂H₁₂)CrO(H_1.5PO₄)₂·H₂O has been synthesized hydrothermally using piperazine as organic template. Its crystal structure was solved ab initio using synchrotron powder X-ray diffraction data [monoclinic, a = 16.9649(4) Å, b = 9.8609(2) Å, c = 7.14375(14) Å, and β = 94.896(3)°, space group P2₁/a, Z = 4]. 1D structure is composed by isolated infinite anionic chains [CrO(H_1.5PO₄)₂]_n (vertex-sharing {CrO₆} octahedra joined by phosphate moieties). Their 2D plate-like morphology is propitiated by a very strong inter-chain interaction (P–O···H···O–P symmetric hydrogen bonds). KAS isoconversional method was applied to determine the activation energy for both thermal and thermo-oxidative decomposition of (C₄N₂H₁₂)CrO(H_1.5PO₄)₂·H₂O.     

Fibonacci numbers and real quadratic p-rational fields

Periodica Mathematica Hungarica - We characterize p-rational real quadratic fields in terms of generalized Fibonacci numbers. We then use this characterization to give numerical evidence to a...     

Electronic Metal–Support Interactions in Single‐Atom Catalysts

The synthesis of single‐atom catalysts and the control of the electronic properties of catalytic sites to arrive at superior catalysts is a major challenge in heterogeneous catalysis. A stable supported single‐atom silver catalyst with a controllable electronic state was obtained by anti‐Ostwald ripening. An electronic perturbation of the catalytic sites that is induced by a subtle change in the structure of the support has a strong influence on the intrinsic reactivity. The higher depletion of the 4d electronic state of the silver atoms causes stronger electronic metal–support interactions, which leads to easier reducibility and higher catalytic activity. These results may improve our understanding of the nature of electronic metal–support interactions and lead to structure–activity correlations.     

Yttrium-succinates coordination polymers: Hydrothermal synthesis, crystal structure and thermal decomposition

New polymeric yttrium-succinates, Y₂(C₄H₄O₄)₃(H₂O)₄·6H₂O and Y₂(C₄H₄O₄)₃(H₂O)₂, have been synthesized, and their structures (solved by single crystal XRD) are compared with that of Y₂(C₄H₄O₄)₃(H₂O)₂·H₂O. Three compounds were obtained as single phases, and their thermal behaviour is described.     

Ammonium-exchanged phase of γ-titanium phosphate

The monoammonium salt of γ-titanium phosphate has been prepared by hydrothermal treatment of π-Ti₂O(PO₄)₂·2H₂O in the presence of urea and phosphoric acid, and its crystal structure was obtained by Rietveld analysis using powder X-ray diffraction data. γ-Ti(PO₄)(NH₄HPO₄) crystallizes in the monoclinic space group P2₁/m with a = 5.0725(3) Å, b = 6.3101(3) Å, c = 11.2435(5) Å, β = 97.980(3)° (Z = 2). The structure consists of 2D titanium phosphate layers in the ab-plane. The titanium atoms and one of the phosphate groups are located nearly in the ab-plane of the layer. All the oxygen atoms of this phosphate group are involved in titanium coordination sphere. The other phosphate group located in the layers edges links two neighboring titanium atoms in the a-direction through two of its oxygen atoms. The remaining two oxygens are pointed toward the interlayer space being involved in hydrogen bond interactions with the ammonium ions. Each ammonium ion is shared by four oxygens belonging to four different phosphate hydroxyl groups. γ-Ti(PO₄)(NH₄HPO₄) is stable until 453 K, while above this temperature, it transforms to γ’-Ti(PO₄)(NH₄HPO₄) high temperature polymorph stable until 573 K. Thermal decomposition of this material leads to cubic TiP₂O₇ structure, with previous formation of two intermediate pseudo-layered compounds: Ti(PO₄)(NH₄HP₂O₇)_0.5 and Ti(PO₄)(H₂P₂O₇)_0.5. The activation energy of thermal decomposition has been calculated as a function of the extent of conversion applying the Kissinger–Akahira–Sunose (KAS) isoconversional method to the thermogravimetric data.     

Series of metal organic frameworks assembled from Ln(III), Na(I), and chiral flexible-achiral rigid dicarboxylates exhibiting tunable UV-vis-IR light emission

Two series of isoreticular chiral metal-organic frameworks assembled from Ln(III) (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb), Na(I), and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaLn(Tart)(BDC)(H(2)O)(2)] (S1) and [NaLn(Tart)(biBDC)(H(2)O)(2)] (S2) (H(2)Tart = tartaric acid; H(2)BDC = terephthalic acid; H(2)biBDC = biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. The compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TG-MS and DSC), vibrational spectroscopy (FTIR), scanning electron microscopy (SEM-EDX), elemental analysis, and X-ray thermodiffractometry. The catalytic activity has been also investigated. The photoluminescence properties of selected compounds have been investigated, exhibiting room temperature tunable UV-vis-IR light emission.