A. P. Bobylev

Synthesis and crystal structure of new complex sodium lanthanide phosphate molybdates Na2MIII(MoO4)(PO4)(MIII = Tb, Dy, Ho, Er, Tm, Lu)

New complex sodium lanthanide phosphate molybdates Na2MIII(MoO4)(PO4)(MIII=Tb, Dy, Ho, Er, Tm, Lu) have been synthesized by the ceramic method (T = 600°C, τ = 48 h), and their unit cell parameters have been determined. The structures of Na2MIII(MoO4)(PO4)(MIII = Dy, Ho, Er, Lu) were refined by the Rietveld method. The compounds are isostructural: they are orthorhombic (space group Ibca, Z = 8) and have layered structures. In the structures of phosphate molybdates, chains of MIIIO8 polyhedra and MoO4 tetrahedra are linked by PO4 tetrahedra to form layers. The MoO42− anions are involved in dipole-dipole interaction. The sodium ions are arranged in the interlayer space. The compounds melt incongruently at 850–870°C.

New complex ytterbium molybdophosphates M 2 I Yb(PO4)(MoO4) (MI = K, Na): Synthesis and structure solution

Complex rare-earth molybdophosphates of sodium and potassium (Na2Yb(PO4)(MoO4) (I) and K2Yb(PO4)(MoO4) (II) are synthesized by solid-phase reactions at 600°C (for I) and 750°C (for II). The molybdophosphates are characterized using powder X-ray diffraction, laser second harmonic generation (SHG), IR spectroscopy, and differential thermal analysis. Their structures are refined using the Rietveld technique. The compounds are isostructural and crystallize in an orthorhombic system (space group Ibca, Z = 8). The unit cell parameters are a = 18.0086(1) Å, b = 12.0266(1) Å, c = 6.7742(1) Å for compound I and a = 19.6646(1) Å, b = 12.0570(1) Å, c = 6.8029(1) Å for compound II. The structures are built of YbO8 chains extended along axis c and linked into layers through PO4 tetrahedra. The Na+ cations (CN = 6) and the K+ cations (CN = 8) reside in the interlayer spaces.

Indium strontium hydrogen phosphate SrIn2[PO3(OH)]4: Synthesis and crystal structure

Indium strontium hydrogen nitrate SrIn2[PO3(OH)]4 was synthesized under mild hydrothermal conditions (T = 180 or 200°C) and characterized using IR spectroscopy, chemical analysis, and thermal analysis. A structure model obtained ab initio was refined by the Rietveld method: a= 9.6412(1) Å, b = 13.763(1) Å, c = 9.3579(1) Å, Robs = 0.0183, Rp = 0.0493 (space group B2212, Z = 4). The acentricity of the structure was confirmed by SHG tests (I2ω/I2ω(SiO2) ≈ 2.0). In the SrIn2[PO3(OH)]4 structure, indium atoms reside in distorted InO6 octahedra and form, together with PO3(OH) tetrahedra, a mixed 3D structure {In2[PO3(OH)]4}3∞2− whose voids are occupied by Sr2+ cations (CN = 8). The block-dimer In2(HPO4)10 is the most informative unit of the framework. Blocks are condensed into infinite columns running in the [101] direction. The compound is thermally stable up to 400°C.

The substitution of cations by magnesium in the structure K3Ho(VO4)2

Abstract The cation substitutions in the crystal lattice of binary potassium–holmium vanadate (V) K 3 Ho(VO 4 ) 2 by magnesium have been studied using various types of chemical solid state reactions. It was shown that in the presence of the quasi-ternary system K 3 VO 4 –Mg 3 (VO 4 ) 2 –HoVO 4 at 700°C there a compound defined as K 3 Ho(VO 4 ) 2 with a narrow homogeneity range where K and Ho are partially substituted by Mg in accordance with various schemes.

Hydrothermal synthesis and crystal structure of a new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4

A new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4 was synthesized under mild hydrothermal conditions (200°C, τ = 168 h). The equimolar content of Ga and P was determined by chemical analysis and electron probe X-ray microanalysis. The presence of NH4 and OH groups was demonstrated by IR and Raman spectroscopy. An ab initio model of the crystal structure was refined by the Rietveld method (space group P21/m, Z = 2): a = 4.4832(1) Å, b = 6.0430(1) Å, c = 8.5674(1) Å, β = 98.019(1)°, Rp = 0.0552, Rwp = 0.0723. A zero SHG signal (T = 300 K) confirmed a centrosymmetric structure of the compound. The structure contains layers composed of GaO4(OH)2 octahedra and PO4 tetrahedra. The interlayer space accommodates ammonium cations. The layer is based on linear chains of edge-sharing GaO4(OH)2 octahedra with a zigzag trans-arranged-Ga-(OH)-Ga-(OH)-backbone. The construction of the layer in (NH4)Ga(OH)PO4 was found to be topologically related to that in (En)0.5Fe(OH)PO4. The effect of the gradual F− → OH− substitution in the quasi-morphotropic series (NH4)GaF1-δ(OH)δPO4 (δ = 0, 0.5, 1.0) on the degree of polarization of the mixed anionic radical was considered. (NH4)Ga(OH)PO4 is thermally unstable: removal of NH3 and H2O molecules in the range 170–450°C is accompanied by the formation of two polymorphs of GaPO4.