Band 229, Heft 12

The new polymorph of Co 2 [PO 4 ]F has been synthesized by a hydrothermal route. Its crystal structure was determined from single-crystal X-ray diffraction data. Co 2 [PO 4 ]F crystallizes with the triplite-type structure, space group C 2 /c , a =12.856(2), b =6.4369(10), c =9.6742(16) Å, β =117.40(1)°, V =710.7(2) Å 3 and Z =8. The structure consists of a 3D-framework buildup of condensed PO 4 tetrahedra, and cobalt(II) polyhedra which form chains running along the [101] and [010] directions. The coordination of the cobalt cations and the connectivity between the cobalt polyhedra are not well defined due to the disorder of the fluoride anions which form zigzag chains along [001]. The theoretical ordering of the fluoride anions led to two different structural models, very similar to the triplite Cc- CoFe[PO 4 ]F and the triploidite P 2 1 / c -Co 2 [PO 4 ]F, and in which the cobalt atoms are five and six coordinated.

Ferdowsiite is monoclinic, a =8.677(2) Å, b =5.799(1) Å, c =13.839(3) Å, β=96.175(4)°, unit cell volume 692.3 Å 3 . Space group P 2 1 / n . Refinement from single-crystal X-ray diffraction data reached R 1 =0.028 for 626 F o >4σ( F o ) and 0.032 for all 716 F o used. Value of wR 2 is 0.065. The crystal structure of ferdowsiite, approximately Ag 8 Sb 4 (As,Sb) 4 S 16 , contains four distinct cation and four different anion sites in the asymmetric unit, all in general positions. Besides two Ag sites and one Sb site, the crystal structure contains one mixed As-Sb coordination polyhedron (0.63 As and 0.37 Sb in the site). The Sb1 site has three short Sb-S bonds 2.503–2.645 Å. As and Sb in the mixed site were refined separately, with isotropic displacement coefficients. As has typical bond length values of 2.248–2.354 Å whereas Sb has 2.443–2.392 Å, i.e., the observed ligand positions are visibly influenced by the predominant arsenic. The crystal structure of ferdowsiite is a superstructure of a PbS like motif. The {100} planes of the PbS-like substructure are the (105̅), (301) and (010) planes in terms of the ferdowsiite lattice. The structure contains zig-zag chains of Sb1 connected via short Sb-S bonds and flanked by (Sb,As)S 3 groups and Ag polyhedra. Groups of four SbS 5 -and (Sb,As)S 5 coordination pyramids form an interconnected network with interspaces which accommodate both the lone electron pairs and the tetrahedrally coordinated Ag situated in coordination octahedra. Partial lead substitution takes place in the coordination polyhedra of Sb1 and Ag2. In the paper, the structure is compared with the other Ag(As,Sb,Bi)(S,Se) 2 structures. The configurationally closest PbS-based homeotypic structure, however, is diaphorite, which is an ordered superstructure of the ferdowsiite arrangement, with a substantial presence of Pb, and without As.

Lithium tungsten bronzes with a nominal composition of Li 0.4 WO 3 were synthesized by solid state reactions in silica tubes at 973 K and various low pressures. Samples were characterized using X-ray single crystal and powder diffraction, and neutron powder diffraction. The air pressure inside the sealed quartz tubes played roles for the formation of Li 0.4 WO 3 phases with different symmetries. Whereas using a pressure of 10 –7 MPa a pure body centered cubic ( Im 3¯$\bar 3$) tungsten bronze was formed, at higher pressures (>10 –7 MPa) a mixture of Im 3¯$\bar 3$ and primitive cubic ( Pm 3¯$\bar 3$ m ) perovskite tungsten bronzes were observed with pressure dependent phase fractions. While keeping the synthesized samples under open atmospheric conditions the Im 3¯$\bar 3$ phase gradually transformed into a tetragonal perovskite ( P 4/ nmm ) tungsten bronze. The slow cubic into tetragonal phase transformation has been explained in terms of the mobility of lithium within two different crystallographic sites.

In this report, we summarize our experimental and theoretical investigations in the zinc(II) imidazolate, [Zn(im) 2 ], and zinc(II) 4,5-dichloroimidazolate, [Zn(dcim) 2 ], systems that have been published previously. This comprises a study on the thermodynamic stabilities of the two densest phases with coi and zni framework structures in the [Zn(im) 2 ] system including the discovery and characterization of a new [Zn(im) 2 ·0.5py]-neb phase (py = pyridine), a study on the mechanism of formation of the [Zn(im) 2 ]-zni phase as well as a study on the discovery and characterization of a new [Zn(dcim) 2 ]-SOD phase. In addition, we present as yet unpublished work. This concerns the discovery and characterization of a new [Zn(im) 2 ·0.5mor]-neb phase (mor = morpholine) and investigations of the mechanisms of crystallization of [Zn(im) 2 ·0.5py]-neb and [Zn(im) 2 ·0.5mor]-neb as well as an evalutation of time-resolved SAXS/WAXS data recorded in-situ during the formation of [Zn(im) 2 ]-zni.

A new hydrogen-containing Ca 9 (Fe 0.63 Mg 0.37 )H 0.37 (PO 4 ) 7 phosphate with the whitlockite-type structure has been synthesized by a hydrothermal method and its structure has been studied by the single-crystal X-ray diffraction. The compound crystallizes in the trigonal space group R 3 c (traditional for compounds with the whitlockite-type structure) with unit-cell parameters: a =10.3533(1) Å, c =37.1097(4) Å. The structure has been determined using the “charge flipping” method. Ca 9 (Fe 0.63 Mg 0.37 )H 0.37 (PO 4 ) 7 structure is similar to that of other members of the whitlockite-type family. The presence of hydrogen in the structure leads to the formation of OH-group with one of the oxygen of PO 4 -tetrahedra. Based on an analysis of the bond valence sums (BVS) a conclusion has been made about localization of H atoms in the structure. Smaller values of BVS for O1 and O10 atoms than ones for other oxygen atoms indicate localization of H atoms between them in a position with site symmetry 18 b .

A solid state melting and annealing route was used to prepare Cu 6 Te 3 S, a copper telluride sulfide representing a filled variant of the Cr 3 Si structure type. The title compound exhibits a reversible phase transition at 404 K which was confirmed by thermal analysis, temperature dependent X-ray single crystal and powder diffractometry. Both polymorphs crystalize cubic in space groups P4¯3n$P\bar 43n$ and P 2 1 3, respectively. X-ray photoelectron spectroscopy (XPS) was performed to evaluate the electronic structure of Cu 6 Te 3 S and to determine the oxidation state of Cu in the title compound.