Stabilization of Pr4+ in Silicates─High-Pressure Synthesis of PrSi3O8 and Pr2Si7O18

The reaction between PrO2 and SiO2 was investigated at various pressure points up to 29 GPa in a diamond anvil cell using laser heating and in situ single-crystal structure analysis. The pressure points at 5 and 10 GPa produced Pr2III(Si2O7), whereas Pr4IIISi3O12 and Pr2IV(O2)O3 were obtained at 15 GPa. Pr4IIISi3O12 can be interpreted as a high-pressure modification of the still unknown orthosilicate Pr4III(SiO4)3. PrIVSi3O8 and Pr2IVSi7O18 that contain praseodymium in its rare + IV oxidation state were identified at 29 GPa. After the pressure was released from the reaction chamber, the Pr(IV) silicates could be recovered, indicating that they are metastable at ambient pressure. Density functional theory calculations of the electronic structure corroborate the oxidation state of praseodymium in both PrIVSi3O8 and Pr2IVSi7O18. Both silicates are the first structurally characterized representatives of Pr4+-containing salts with oxoanions. All three silicates contain condensed networks of [SiO6] octahedra which is unprecedented in the rich chemistry of lanthanoid silicates.

Convenient chirality transfer from organics to titania: construction and optical properties

Polyethyleneimine (PEI) complexed with chiral d- (or l-) tartaric acid (tart) in water can self-organize into chiral and crystalline PEI/tart assemblies. It has been previously confirmed that the complexes of PEI/tart could work as catalytic/chiral templates to induce the deposition of SiO2 nanofibres with optical activity but without outwards shape chirality such as helices. In this work, we found that the templating functions of PEI/tart were still effective to prompt the deposition of TiO2 to form chiral PEI/tart@TiO2 hybrid nanofibres under aqueous and room temperature conditions within two hours. Furthermore, the co-deposition of TiO2 and SiO2 was also fulfilled to yield chiral PEI/tart@TiO2/SiO2 nanofibres. These TiO2-containing hybrid nanofibres showed non-helical shapes on the length scale; however, chiroptical signals with mirror relation around the UV-Vis absorption band of TiO2 remarkably appeared on their circular dichroism (CD) spectra. By means of the protocols of XRD, TEM, SEM, UV-Vis, CD and XPS, structural features and thermoproperties of the chiral TiO2 and SiO2/TiO2 were investigated.

High-pressure synthesis, crystal structure and photoluminescence properties of a new terbium silicate: Na2Tb1.08Ca2.92Si6O18H0.8

New terbium silicate Na₂Tb_1.08Ca_2.92Si₆O₁₈H_0.8 was synthesized at high pressure condition. The structure was and the photoluminescence properties were also investigated suggesting a strong green emission with the lifetime 2.498(7) ms.

Synthesis, crystal structure, and luminescence properties of a new europium silicate

A new europium silicate, NaEuSi₃O₇(OH)₂ (denoted as 1), was synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD) analyses.

Novel open-framework europium silicates prepared under high-temperature and high-pressure conditions

Two new europium silicates, Na15Eu3Si12O36 (denoted as 1) and K2EuSi4O10F (denoted as 2), were successfully synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD). The single-crystal XRD analysis of 1 reveals that its structure is based on [Si6O18]n(12n-) cyclosilicate anions that are built from six SiO4 tetrahedra sharing two of their four O corners with each other. Such [Si6O18]n(12n-) cyclosilicate anions are linked via EuO6 octahedra to form a three-dimensional (3D) framework containing 6-membered ring channels delimited by the SiO4 tetrahedra and EuO6 octahedra along the [010] direction. The structure of 2 consists of infinite tubular chains of corner-sharing SiO4 tetrahedra, which are further linked together via corner sharing O atoms by infinite chains of EuO4F2 octahedra forming a 3-D framework that contains 8-ring and 6-ring channels along the [010] direction. The photoluminescence properties of 1 and 2 were also investigated.