Two Structure Types Based on Si 6 O 15 Rings: Synthesis and Structural and Spectroscopic Characterisation of Cs 1.86 K 1.14 DySi 6 O 15 and Cs 1.6 K 1.4 SmSi 6 O 15

The layer silicate Cs2SnIVSi6O15

Single crystals of Cs2SnSi6O15, dicaesium tin(IV) hexa-silicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO2 in a closed silica ampoule. The crystal structure of Cs2SnSi6O15 is constructed from {Si6O15}6- layers extending parallel to (101), and CsI cations with a coordination number of eleven as well as isolated [SnO6] octa-hedra situated between the silicate layers. Each of the nine different SiO4 tetra-hedra in the silicate layer has a connectedness of Q 3 (three bridging and one terminal O atom), which leads to the formation of five- and eight-membered rings. The same type of silicate layer is found in the crystal structure of the mineral zeravshanite. Comparison with other silicates of the type Cs2 M IVSi6O15 (M IV = Ti, Zr, Th, U) revealed a klassengleiche group-subgroup relationship of index 2 between Cs2ZrSi6O15 (Z = 6, space group C2/m) and Cs2SnSi6O15 (Z = 12, space group I2/c).

Chemistry of Metal Silicates and Germanates: The Largest Metal Polygermanate, K11Mn21Ge32O86(OH)9(H2O), with a 76 Å Periodic Lattice

An examination of manganese silicates and germanates revealed unusual structural motifs and extremely different chemistries, with identical hydrothermal reactions forming K₂Mn₂Si₃O₉ versus K₁₁Mn₂₁Ge₃₂O₈₆(OH)₉(H₂O). The germanate is exceptional in both its c-axis length (exceeding 76 Å) and unit cell volume (nearly 18000 ų), the largest known polygermanate structure to our knowledge.

A Cesium Rare-Earth Silicate Cs3 RESi6 O15 (RE=Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57 Å Unit Cell Axis

The structure of Cs₃ RESi₆ O₁₅ , where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si₆ O₁₅ framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 Å) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc³⁺ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 °C) hydrothermal method with CsOH and F^- mineralizers. The presence of fluoride is essential to the formation of the product.

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.

(3+1)-Incommensurately modulated crystal structure of Cs3ScSi6O15

Single-crystal X-ray diffraction of Cs3ScSi6O15 shows the presence of main reflections and satellite reflections up to the fourth order along the c* direction. The (3+1)-dimensional incommensurately modulated structure was solved in superspace group X3m1(00gamma)0s0 [a = 13.861 (1), c = 6.992 (1) Å, V = 1163.4 (2) Å(3)] with a modulation wavevector q = 0.14153 (2)c*. Refinement of three modulation waves for positional and anisotropic displacement parameter values for all atoms converged to R(obs) values for all, main and satellite reflections of first, second and third order of 0.0200, 0.0166, 0.0181, 0.0214 and 0.0303, respectively. Cs3ScSi6O15 forms a mixed tetrahedral-octahedral framework with prominent six-membered rings of [SiO4]-tetrahedra interconnected by [ScO6]-octahedra. Apart from Sc, all atoms are strongly affected by positional modulation with maximum atomic displacements of up to 0.93 Å causing rigid polyhedral arrangements to perform tilt and twist movements relative to each other, such as a rotation of the Sc-octahedra around the 3-axis by over 38°. Cs has an irregular coordination environment; however, considering distances up to 3.5 Å, the bond-valence sum changes by no more than 0.02 as a function of t and thus overall kept at a level of ca 1.075.

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.