Synergetic Influence of Alkali-Metal and Lone-Pair Cations on Frameworks of Tellurites.

Four new tellurites were hydrothermally synthesized by the adjustment of different alkali-metal ions, and all of the compounds demonstrate 2D layer structures. Rb2Te4O9·2H2O in centrosymmetric space group Pccn features a new [Te4O9]∞2- anion sheet consisting of rare [Te8O22]12- groups. RbNaTe8O14(OH)6·8H2O in CS space group P1̅ exhibits a [Te4O9]∞2- anion layer by linkage of the TeO3 and TeO4 units. NaPb4Te4O12F located in CS space group P4/ n displays an unusual [PbTeO3]∞ neutral layer made up of PbO3 and TeO3 trigonal pyramids. RbK3Te8O18·5H2O lying in noncentrosymmetric (NCS) space group Cc shows a [Te4O9]∞2- anion layer composed of the TeO3 and TeO4 units; its second-harmonic-generation response is about 0.2 times that of KH2PO4; structure analysis and local dipole moment calculation verify that the weak polarization mostly from the [Te4O9]∞2- layer results from the inverse arrangement of TeO n units, and further theoretical calculation confirms that TeO n groups dominate the band gap of RbK3Te8O18·5H2O and optical properties. Meanwhile, systematic analyses of a series of metal tellurites reveal that the alkali-metal cations exert a considerable impact on polarization of the crystal structures, which puts forward a feasible idea about the design of new NCS materials.

Li6Na3Sr14Al11P22O90: an oxo-centered Al3 cluster based phosphate constructed from two types of (3,6)-connected kgd layers.

A novel and thermally stable aluminum phosphate Li6Na3Sr14Al11P22O90 (1) has been achieved by using a solid-state molten method, which contains an oxo-centered trinuclear cluster and an anti-Lowenstein's rule Al-O-Al linkage and is constructed from two types of (3,6)-connected kgd layers [Al(Al3O)(PO4)7]25- and [Al(PO4)2]3-. The good optical transparency in the whole UV range and excellent thermal stability make the title compound a potential optical window material.