Structural characterization of quaternary selenites of tungsten(VI), A 2W3SeO12 (A = NH4, Cs, Rb, K or Tl)

The quaternary A 2W3SeO12 (A = NH4, Cs, Rb, K or Tl) selenites have been prepared in the form of single crystals by hydrothermal and novel solid-state reactions. They were characterized by X-ray diffraction, thermal and spectroscopic studies. All of them have a hexagonal tungsten oxide (HTO) related [W3SeO12]2− anionic framework with pyramidally coordinated Se4+ ions. The known A 2W3SeO12 (A = NH4, Cs or Rb) compounds are isostructural with the Cs2W3TeO12 compound and have a non-centrosymmetric layered structure containing intra-layer Se—O bonds. The new compound K2W3SeO12(α) is isostructural with the K2W3TeO12 compound and has a centrosymmetric three-dimensional structure containing interlayer Se—O bonds. It is inferred that the new Tl2W3SeO12 compound has the same three-dimensional structure as K2W3SeO12(α).

Elucidation of the Mechanism of Phase Transition in a Zinc Formate Framework Templated by a Diammonium Cation—Structural, Phonon and Dielectric Studies

In this paper we present the synthesis method and a detailed description of the crystal structure, as well as thermal, dielectric and phonon properties, of the [CH3NH2CH2CH2NH2CH3][Zn2(HCOO)6] (dmenH2-Zn) metal organic framework. The negative charge of the anionic framework ([Zn2(HCOO)6]2-) is balanced by N,N′-dimethylethylenediamine (dmenH22+) ions located in the voids of the framework. Thermal analysis revealed that dmenH2-Zn underwent a reversible structural phase transition at around room temperature (Tc~300 K). The single-crystal X-ray diffraction showed that dmenH22+ templates were dynamically disordered at 295 K, since N-H…O bonds were too weak to surmount their thermally activated motions. Reduction in the temperature resulted in ordering of the dmenH22+ cations as a consequence of freezing of their reorientational movements. This behavior caused a symmetry change from P-31c (trigonal) to C 2/c (monoclinic). The mechanism of the observed phase transition of dmenH2-Zn compound was also investigated by temperature-dependent IR measurements. These spectroscopic studies showed that the ordering of the dmenH22+ ions also resulted in the distortion of the anionic framework. Dielectric investigations revealed the occurrence of the dipolar relaxation process clearly defined in the monoclinic phase. The asymmetric shape of the studied process, which indicated a non-Debye-like relaxation, was analyzed using the Havriliak–Negami relaxation function, leading to an Ea value of approximately 0.36 eV.

New nonlinear optical-active AAgGa6S10 (A = K, Rb, Cs) featuring {[AgGa6S10]−}∞ framework and high laser damage threshold

New structure-type AAgGa6S10 (A = K, Rb, Cs) featuring unprecedented {[AgGa6S10]−}∞ anionic framework exhibit the largest band gaps among chalcogenides containing independent Ag site, moderate SHG responses and high LIDTs.

Encapsulating organic guest cations in anionic MOFs that exhibit multi-responsive photochromism and photocontrolled luminescence

Two MOF-based host–guest compounds were prepared by incorporating viologen into an anionic framework, and exhibited photochromism upon irradiation with various light sources. Moreover, their luminescence properties can be switched by irradiation.

Synthesis, crystal structure and charge-distribution validation of a new alluaudite-type phosphate, Na2.22Mn0.87In1.68(PO4)3

Na2.22Mn0.87In1.68(PO4)3, sodium manganese indium tris(phosphate) (2.22/0.87/1.68), was obtained in the form of single crystals by a flux method and was structurally characterized by single-crystal X-ray diffraction. The compound belongs to the alluaudite structure type (space group C2/c) with general formula X(2)X(1)M(1)M(2)2(PO4)3. The X(2) and X(1) sites are partially occupied by sodium [occupancy 0.7676 (17) and 1/2] while the M(1) and M(2) sites are fully occupied within a mixed distribution of sodium/manganese(II) and manganese(II)/indium, respectively. The three-dimensional anionic framework is built up on the basis of M(2)2O10 dimers that share opposite edges with M(1)O6 octahedra, thus forming infinite chains extending parallel to [10\overline{1}]. The linkage between these chains is ensured by PO4 tetrahedra through common vertices. The three-dimensional network thus constructed delimits two types of hexagonal channels, resulting from the catenation of M(2)2O10 dimers, M(1)O6 octahedra and PO4 tetrahedra through edge- and corner-sharing. The channels are occupied by Na+ cations with coordination numbers of seven and eight.