The crystal structure of KAlGeO₄

Abstract

Crystals of the compound KAlGe04 were synthesized under hydrothermal conditions. The space group is P63 with the lattice dimensions a = 18.413 Ä, c = 8.590 Ä and Z = 24. The crystal structure has been redetermined by direct methods and refined by least-squares methods to an R index of 0.094 using three-dimensional diffractometer data. Further refinement assuming a mirror twin with twinning plane (1T0) converged at R = 0.035. The optically active KAlGe04 is composed of an ordered Al, Ge framework with channels of six-membered rings parallel to the crystallographic c-axis. These cavities contain the K cations. Most of the crystals were twinned by merohedry parallel to (110).

Crystal Chemistry and Polymorphism of Potassium–Magnesium Monophosphate

“…Actually, a tridymite framework tends to adopt a higher symmetry if the stuffing cation is bulky, that is, if it fully fills the large cavities. Low-temperature diffraction would be necessary to study -RbMgPO (2) and -CsMgPO , but one can doubt that Rb> and Cs> may fit in a site reduced by the collapsing of the oxygen framework resulting of the existence of MgO polyhedra. The case of TlMgPO is somewhat different because of the higher electronegativity and the stereochemical activity of the 6s lone pair of thallium, so it cannot be put forward for comparison.…”

The Stuffed Framework Structure of BaGa2O4

“…O is isotypic with the structure of KAlGeO (20,21) and belongs to the group of stu!ed framework structures consisting of sequences of tetrahedral layers. Each layer perpendicular to [001] is composed of trigonally shaped 6-membered rings (S6R) of GaO tetrahedra forming honeycomb-like nets.…”

Synthesis and Crystal Structure of the New High‐Pressure Phase CdB2O4

“…Related compounds: The structure of CdB 2 O 4 is closely related to the structure-type of the compounds BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] CaP 2 N 4 , [37] and SrP 2 N 4 . [38] Both structure types consist of layers of tetrahedra, forming "sechser" rings [39,40] with an identical orientation of the tetrahedra.…”

“…Table 2 In SrP 2 N 4 , this superstructure is caused by avoiding one P À N À P angle of 1808 at nitrogen N15. The isotypic compounds BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] and CaP 2 N 4 [37] do not show the linear arrangement at the corresponding position. By contrast, the associated BÀOÀB angle in CdB 2 O 4 adopts a value of 1808 at oxygen O1 on thermal average ( Figure 6).…”

“…We report the synthesis and the crystal structure of this compound, including a comparative discussion concerning the related structures of BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] CaP 2 N 4 [37] and SrP 2 N 4 . [38] In contrast to CdB 2 O 4 , all these phases form a superstructure, whereas CdB 2 O 4 exhibits the basic structure of this family for the first time.…”