Dilead mercury chromate(VI), Pb2HgCrO6

The structure of Pb₂HgCrO₆ (space group P) can be described as consisting of isolated [CrO₄]^2? tetrahedra and nearly linear [HgO₂]^2? dumb‐bells, which form layers of composition [HgCrO₆]^4?. These are intercalated with corrugated pseudo‐hexagonal Pb²⁺ layers. The Pb²⁺ cation is stereochemically active and has coordination 3+5.     

Dilead(II) trimercury(II) tetraoxide chromate(VI), Pb2(Hg3O4)(CrO4)

Pb₂(Hg₃O₄)(CrO₄) consists of [CrO₄]²⁻ tetra­hedra, linear O—Hg—O dumbbells and divalent Pb atoms in [3+5]‐coordination. The HgO₂ dumbbells are condensed into [Hg₃O₄]²⁻ units and can be regarded as a section of the HgO structure. The [Hg₃O₄]²⁻ complex anions are connected by inter­stitial Pb²⁺ ions, while the [CrO₄]²⁻ tetra­hedra are isolated.     

Dipotassium trimanganese(II) tetrakis(hydrogenphosphite), K2[Mn3(HPO3)4]

The title compound is a new mixed alkali/3d metal phosphite. It exhibits a layered structure formed by linear Mn₃O₁₂ trimer units which contain face‐sharing MnO₆ octahedra interconnected by (HPO₃)²⁻ phosphite oxoanions. The K⁺ cations located between the anionic [Mn₃(HPO₃)₄]²⁻ sheets are ninefold coordinated. The presence of the alkaline ion leads to the highest symmetry and shortest interlayer distance compared with two previous compounds showing the same anionic framework and having ammonium salts as cations. The compound crystallizes in the space group Rm, with two crystallographically independent Mn atoms occupying sites of m and 3m symmetry. All the other atoms, except for the phosphite O atoms, are located on special positions with 3m symmetry.     

Cluster self-organization of germanate systems: Suprapolyhedral precursor clusters and self-assembly of K2Nd4Ge4O13(OH)4, K2YbGe4O10(OH), K2Sc2Ge2O7(OH)2, and KScGe2O6(PYR)

Geometric and topological analysis of all known types of K,TR germanates (TR = La-Lu, Y, Sc, In) is carried out with the use of computer techniques (the TOPOS 4.0 program package). Framework structures are represented as three-dimensional (3D) K,TR,Ge networks (graphs) with oxygen atoms removed. The following crystal-forming 2D TR,Ge networks are determined: for K₂Nd₄Ge₄O₁₃(OH)₄, this is TR 4 3 3 4 3 3 + T 4 3 4 3; for K₂YbGe₄O₁₀(OH), this is TR 6 6 3 6 + T 1 6 8 6 + T 2 3 6 8; for K₂Sc₂Ge₂O₇(OH)₂, this is TR 6 4 6 4 + T 6 4 6; and for KScGe₂O₆, TR 6 6 3 6 3 4 + T 1 6 3 6 + T 2 6 4 3. The full 3D reconstruction of the self-assembly mechanism of crystal structures is performed as follows: precursor cluster—primary chain—microlayer-microframework (supraprecursor). In K₂Nd₄Ge₄O₁₃(OH)₄, K₂Sc₂Ge₂O₇(OH)₂, and KScGe₂O₆, an invariant type of cyclic six-polyhedral precursor cluster is identified; this precursor clusters is built of TR octahedra, which are stabilized by atoms K. For K₂Nd₄Ge₄O₁₃(OH)₄, the type of cyclic four-polyhedral precursor cluster of tetrahedron-linked TR octatopes is identified. The cluster coordination number in a layer is six (the maximum possible value) only for anhydrous germanate KScGe₂O₆ (an analogue of pyroxene, PYR); in the other OH-containing germanates, this number is four. The mechanism of formation of Ge radicals in the form of groups Ge₂O₇ and Ge₄O₁₃, a chain GeO₃, and a tubular assembly of linked cyclic groups Ge₈O₂₀ is considered.     

Cu(Cu0.44Cr4.56)Ge2O12: a close‐packed oxide with CuO4 tetra­hedra

The structure of copper(I,II) penta­chromium(III) germanate, Cu(Cu_0.44Cr_4.56)Ge₂O₁₂, contains one Cu position (m2m), one Ge position (m) and three Cr positions (2/m, m and 2). The close‐packed structure is described in terms of slabs of edge‐sharing Cr³⁺O₆ octa­hedra and isolated CuO₄ and GeO₄ tetra­hedra. These slabs are aligned parallel to the bc plane and are separated from each other by GeO₄ tetra­hedra along a. The tetra­hedral coordination observed for the Cu⁺/Cu²⁺ ions represents an unusual feature of the structure. The Cr—O and Cu—O bond lengths are compared with literature data.     

Disilberoxotellurat(VI), Ag2TeO4

Disilver Oxotellurate(VI), Ag₂TeO₄ Ag₂TeO₄ was synthesised by reaction of Ag₂O and TeO₂ applying an elevated oxygen pressure. According to a single crystal structure determination (C2/c, a = 9.0588(9), b = 9.2456(8), c = 13.623(1) Å, β = 91.758(8)°, Z = 12, 1289 independent reflections, R1 = 2.32 %, wR2 = 5.51 %), Ag₂TeO₄ contains a novel chain‐like polyanion with tellurium in an octahedral coordination. The TeO₆ octahedra are connected via common edges and vertices in a way that the resulting polyanion represents a section of the rutile structure type. Ag₂TeO₄ shows diamagnetic and insulating behaviour, it decomposes at 560 °C into Ag₂TeO₃ and oxygen.     

Complex lanthanide chromate(VI)-phosphates K2R(CrO4)(PO4) (R = Dy-Lu, Y)

The conditions of formation of complex lanthanide chromate(VI)-phosphates K₂R(CrO₄)(PO₄) were found and these compounds were synthesized by solid-state synthesis with variation of the starting compounds, the temperature of synthesis (500–800 °C), and the annealing time (6–200 h). These salts are typical of late lanthanides, R = Dy-Lu, Y. Using lutetium derivatives as examples, it was shown that no similar compounds with lithium or sodium are formed. All the complex chromate(VI)-phosphates obtained decompose under static conditions at temperatures above 550 °C. They are isostructural and crystallize in the monoclinic system. The unit cell parameters for thulium, ytterbium, and lutetium compounds were calculated. It is shown by IR spectroscopy that PO₄ tetrahedra in the crystal lattice of potassium lanthanide chromate(VI)-phosphates are substantially distorted, whereas the CrO₄ tetrahedra retain the regular tetrahedron symmetry (T _d ). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 622–626, April, 2006.     

Tetrapotassium dicarbonato­dioxo­peroxo­uranium(VI) 2.5‐hydrate,K4[U(CO3)2O2(O2)]·2.5H2O

The title compound was obtained by reacting UO₂ powder in 2 M K₂CO₃ with hydrogen peroxide. The compound contains individual [U(CO₃)₂O₂(O₂)]⁴⁻ ions, which are linked via an extended network of K atoms and hydrogen bonding. The U atom is coordinated to two trans‐axial O atoms and six O atoms in the equatorial plane, forming distorted hexagonal bipyramids. The carbonate ligands are bound to the U center in a bidentate manner, with U—O bond distances ranging from 2.438 (5) to 2.488 (5) Å. The peroxo group forms a three‐membered ring with the U atom, with U—O bond distances of 2.256 (6) and 2.240 (6) Å. The U=O bond distances of 1.806 (5) and 1.817 (5) Å, and an O—U—O angle of 175.3 (3)° are characteristic of the linear uranyl(VI) unit.     

β‐K2Cr2O7

The monoclinic modification of dipotassium dichromate, β‐K₂Cr₂O₇, has been synthesized in the K₂Cr₂O₇–H₂O system. The structure consists of K⁺ cations and Cr₂O₇^2? dimers. In contrast with triclinic α‐K₂Cr₂O₇ [Kuz'min, Ilyukhin, Kharitonov & Belov (1969). Krist.Tech. 4 , 441–461], the Cr₂O₇^2? groups in β‐K₂Cr₂O₇ have twofold crystallographic symmetry and are parallel to each other.     

K2[Mo2O4(C2O4)2(H2O)2]·3H2O

The crystal and molecular structure of dipotassium di‐μ‐oxo‐bis[aqua(oxalato‐O¹,O²)oxomolybdenum(III)] trihydrate, K₂­[Mo₂O₄(C₂O₄)₂(H₂O)₂]·3H₂O, has been determined from X‐ray diffraction data. In the dimeric anion, which has approximate twofold symmetry, each Mo atom is in a distorted octahedral coordination, being bonded to one terminal oxo‐O atom, two bridging O atoms, two O atoms from the oxalato ligand and one from the water mol­ecule. Bond lengths trans to the multiple‐bonded terminal oxo ligand are larger than those in the cis position, confirming the trans influence as a generally valid rule.     

A new chromate of tetravalent cerium: Ce2(CrO4)4·2H2O

Dicerium(IV) tetrachromate(VI) dihydrate, Ce(CrO₄)₄·2H₂O, has been prepared from an acidic aqueous solution at room temperature. Its novel crystal structure, which was solved from single‐crystal X‐ray diffraction data, is built from isolated CrO₄ tetrahedra and isolated Ce(O,H₂O)_n (n = 8 and 9) polyhedra. All atoms are in general positions. The mean Ce—O and Cr—O bond lengths are 2.358 and 1.651 Å, respectively. Comparisons are drawn with the structure of Ce^IV(CrO₄)₂·2H₂O.