Yttrium pyrogermanate,Y2Ge2O7

The structure of diyttrium digermanate, Y₂Ge₂O₇, has been determined in the tetragonal space group P4₃2₁2. It contains one Y, one Ge (both site symmetry 1 on general position 8b) and four O atoms [one on special position 4a (site symmetry ..2) and the remaining three on general positions 8b]. The basic units of the structure are isolated Ge₂O₇ groups, sharing one common O atom and displaying a Ge—O—Ge angle of 134.9 (3)°, and infinite helical chains of pentagonal YO₇ dipyramids, parallel to the 4₃ screw axis. The crystal investigated here represents the left‐handed form of the tetragonal R₂Ge₂O₇ compounds (R = Eu³⁺, Tb³⁺, Er³⁺, Tm³⁺ and Lu³⁺).     

The polar phase of Li2Ge4O9 at 298, 150 and 90 K

Dilithium tetragermanate is orthorhombic, space group P2₁ca, at 298 K, and is thus in a polar and probably a ferroelectric state. The structure contains two independent Li, four Ge and nine O atoms, all on general positions with site symmetry 1. Three tetrahedrally coordinated Ge positions form crumpled crankshaft‐like chains, forming sheets within the ac plane, and these are interconnected by the fourth, octahedrally coordinated, Ge sites along the b direction. The GeO₄ tetrahedra and GeO₆ octahedra form a three‐dimensional framework containing two different cavities, hosting the two 4+1‐coordinated Li sites. Cooling to 90 K does not alter the space‐group symmetry; the tetrahedral chains behave as a rigid unit and changes occur mainly within the Li coordination spheres.     

Synthetic aenigmatite analog Na2(Mn5.26Na0.74)Ge6O20: structure and crystal chemical considerations

Disodium hexamanganese(II,III) germanate is the first aenigmatite‐type compound with significant amounts of manganese. Na₂(Mn_5.26Na_0.74)Ge₆O₂₀ is triclinic and contains two different Na positions, six Ge positions and 20 O positions (all with site symmetry 1 on general position 2i of space group P). Five out of the seven M positions are also on general position 2i, while the remaining two have site symmetry (Wyckoff positions 1f and 1c). The structure can be described in terms of two different layers, A and B, stacked along the [011] direction. Layer A contains pyroxene‐like chains and isolated octahedra, while layer B is built up by slabs of edge‐sharing octahedra connected to one another by bands of Na polyhedra. The GeO₄ tetrahedra show slight polyhedral distortion and are among the most regular found so far in germanate compounds. The M sites of layer A are occupied by highly charged (trivalent) cations, while in layer B a central pyroxene‐like zigzag chain can be identified, which contains divalent (or low‐charged) cations. This applies to the aenigmatite‐type compounds in general and to the title compound in particular.     

In1.06Ho0.94Ge2O7: a thortveitite‐type compound

A new indium holmium digermanate, In_1.06Ho_0.94Ge₂O₇, with a thortveitite‐type structure, has been prepared as a polycrystalline powder material by high‐temperature solid‐state reaction. This new compound crystallizes in the monoclinic system (space group C2/c, No. 15). The structure was characterized by Rietveld refinement of powder laboratory X‐ray diffraction data. The In³⁺ and Ho³⁺ cations occupy the same octahedral site, forming a hexagonal arrangement on the ab plane. In their turn, the hexagonal arrangements of (In/Ho)O₆ octahedral layers are held together by sheets of isolated diortho groups comprised of double tetrahedra sharing a common vertex. In this compound, the Ge₂O₇ diortho groups lose the ideal D_3d point symmetry and also the C_2h point symmetry present in the thortveitite diortho groups. The Ge—O—Ge angle bridging the diortho groups is 160.2 (3)°, compared with 180.0° for Si—O—Si in thortveitite (Sc₂Si₂O₇). The characteristic mirror plane in the thortveitite space group (C2/m, No. 12) is not present in this new thortveitite‐type compound and the diortho groups lose the C_2h point symmetry, reducing to C₂.     

One‐dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O

New decavanadate minerals, the products of the leaching or metasomatic processes, are possible in nature via Na/Rb removal/inclusion reactions. As part of our search for novel vanadate phases with varying functionalities, a new phase, tetrarubidium hexaaquasodium hydrogen decavanadate tetrahydrate, Rb₄[Na(H₂O)₆][HV₁₀O₂₈]·4H₂O, has been synthesized by the hydrothermal technique at 553 K. Ten shared edges of V‐centred octahedra form monoprotonated decavanadate cages, which are joined together via hydrogen bonds into one‐dimensional chains parallel to the [101] direction. Within these chains, H atoms are sandwiched between neighbouring polyanions. Na and Rb atoms and H₂O molecules occupy interstices flanked by the anionic chains providing additional crosslinking in the structure. This compound is the second decavanadate with P2/n symmetry. Structural relationships among protonated and deprotonated decavanadates with inorganic cations, including minerals of the pascoite group, are discussed.     

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.     

Polymeric tris(μ2‐acetone‐κ2O:O)sodium polyiodide at 120 K

In the title compound, [Na(C₃H₆O)₃]_n(I₂)_n, all non‐H atoms are in special positions of the space group P6₃/mcm, with the Na atom in 2b, the I atom in 4c, the carbonyl O atom and the C atom attached to it both in 6g, and the methyl C atom in 12k. The H atoms of the rotationally disordered methyl groups are in 24l general positions but with occupancies of 0.5, because they occur in two sets related by a crystallographic mirror plane. Infinite chains are created by face‐sharing octahedral Na‐coordination polyhedra, with Na—O and Na⋯Na distances of 2.439 (5) and 3.2237 (4) Å, respectively. I atoms form infinite linear chains, in which the I‐atom separation is 3.2237 (4) Å.     

Single Crystal X‐ray Diffraction Study of CsHSi2O5

Hydrothermally synthesized CsHSi₂O₅ was studied by single‐crystal X‐ray diffraction. The compound is orthorhombic (space group Pnma). Unit cell parameters are a = 4.9758(3), b = 8.8089(6), c = 12.9295(9) Å with four formula units per cell. The structure was solved by direct methods and refined to a residual R₁ = 0.025 for 621 independent observed reflections with I > 2σ(I) and 41 parameters. Residual electron densities were used to locate positions of the H atoms. They are part of silanol groups and show a disorder involving two positions related by a center of symmetry. The resulting O—H···O distance of 2.44 Å is one of the shortest hydrogen bonded O···O distances in inorganic compounds containing silanol groups. The structure belongs to the class of unbranched zweier double chain silicates. The [Si₂O₄(OH)^—] chains run parallel [100]. Cesium cations providing additional linkage between the anionic ribbons reside in voids between the chains and coordinate to nine oxygen ligands.     

ACr(C2O4)2(H2O)4 (A = Li or Na): two new coordination polymers of low dimensionality with different hydrogen‐bond networks

Single crystals of two new bimetallic oxalate compounds with the formula [ACr(C₂O₄)₂(H₂O)₄]_n (A = Li or Na), namely catena‐poly[[diaqualithium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquachromium(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], ( I ), and catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[di‐aquachromium(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], ( II ), have been synthesized, characterized and their crystal structures elucidated by X‐ray diffraction analysis and compared. The compounds crystallize in the monoclinic space group C2/m for ( I ) and in the triclinic space group P for ( II ); however, they have somewhat similar features. In the asymmetric unit of ( I ), the Li and Cr atoms both have space‐group‐imposed 2/m site symmetry, while only half of the oxalate ligand is present and two independent water molecules lie on the mirror plane. The water O atoms around the Li atom are disordered over two equivalent positions separated by 0.54 (4) Å. In the asymmetric unit of ( II ), the atoms of one C₂O₄^2? ligand and two independent water molecules are in general positions, and the Na and Cr atoms lie on an inversion centre. Taking into account the symmetry sites of both metallic elements, the unit cells may be described as pseudo‐face‐centred monoclinic for ( I ) and as pseudo‐centred triclinic for ( II ). Both crystal structures are comprised of one‐dimensional chains of alternating trans‐Cr(CO)₄(H₂O)₂ and trans‐A(CO)₄(H₂O)₂ units μ₂‐bridged by bis‐chelating oxalate ligands. The resulting linear chains are parallel to the [101] direction for ( I ) and to the [11] direction for ( II ). Within the two coordination polymers, strong hydrogen bonds result in tetrameric R₄⁴(12) synthons which link the metal chains, thus leading to two‐dimensaional supramolecular architectures. The two structures differ from each other with respect to the symmetry relations inside the ligand, the role of electrostatic forces in the crystal structure and the molecular interactions of the hydrogen‐bonded networks. Moreover, they exhibit the same UV–Vis pattern typical of a Cr^III centrosymmetric geometry, while the IR absorption shows some differences due to the oxalate‐ligand conformation. Polymers ( I ) and ( II ) are also distinguished by a different behaviours during the decomposition process, the precursor ( I ) leading to the oxide LiCrO₂, while the residues of ( II ) consist of a mixture of sodium carbonate and Cr^III oxide.     

Crystal packing of two 5‐substituted 2‐methyl‐4‐nitro‐1H‐imidazoles

Infinite chains connected by N—H...N hydrogen bonding form the primary packing motif in two closely related 4‐nitroimidazole derivatives, viz. 5‐bromo‐2‐methyl‐4‐nitro‐1H‐imidazole, C₄H₄BrN₃O₂, (I), and 2‐methyl‐4‐nitro‐1H‐imidazole‐5‐carbonitrile, C₅H₄N₄O₂, (II). These chains are almost identical, even though in (II) there are two symmetry‐independent molecules in the asymmetric unit. The differences appear in the interactions between the chains; in (I), there are strong C—Br...O halogen bonds, which connect the chains into a two‐dimensional grid, while in (II), the cyano group does not participate in specific interactions and the chains are only loosely connected into a three‐dimensional structure.     

Poly[bis(μ2‐2‐aminopyrazine‐κ2N1:N4)(μ2‐nitrato‐κ2O:O)(nitrato‐κ2O,O′)disilver(I)]: an achiral two‐dimensional coordination polymer forming chiral crystals

The solution reaction of AgNO₃ and 2‐aminopyrazine (apyz) in a 1:1 ratio gives rise to the title compound, [Ag₂(NO₃)₂(C₄H₅N₃)₂]_n, (I), which possesses a chiral crystal structure. In (I), both of the crystallographically independent Ag^I cations are coordinated in tetrahedral geometries by two N atoms from two apyz ligands and two O atoms from nitrate anions; however, the Ag^I centers show two different coordination environments in which one is coordinated by two O atoms from two different symmetry‐related nitrate anions and the second is coordinated by two O atoms from a single nitrate anion. The crystal structure consists of one‐dimensional Ag^I–apyz chains, which are further extended by μ₂‐κ²O:O nitrate anions into a two‐dimensional (4,4) sheet. N—H...O and C_apyz—H...O hydrogen bonds connect neighboring sheets to form a three‐dimensional supramolecular framework.     

catena‐Poly­[[di­aqua­cobalt(II)]‐μ‐oxalato]

Single crystals of the title compound, [Co(C₂O₄)(H₂O)₂]_n, have been prepared by hydro­thermal methods and characterized by X‐ray diffraction analysis. The crystal structure consists of infinite one‐dimensional chains of di­aqua­cobalt(II) units bridged by oxalate groups. These chains lie on twofold symmetry axes parallel to the b axis, and the [Co(C₂O₄)]_n system is nearly planar within experimental error. The cobalt(II) coordination polyhedra are irregular octahedra, with oxalate O atoms at the equatorial positions and water mol­ecules at the axial positions. The chains are linked by hydrogen bonds via the water mol­ecules.     

Dipotassium tetra­chromate(VI), K2Cr4O13

The structure of dipotassium tetra­chromium(VI) trideca­oxide, K₂Cr₄O₁₃, has been determined from single‐crystal X‐ray data collected at 173 (2) K on a racemically twinned crystal with monoclinic Pc space‐group symmetry. The structure is composed of discrete [Cr₄O₁₃]²⁻ zigzag chains held together by the charge‐balancing potassium ions. The conformations adopted by the tetra­chromate anion in alkali metal salts and Cr₈O₂₁ are different and can be divided into three categories.     

catena‐Poly[[(acetato‐κ2O,O′)triaquabarium(II)]‐μ3‐acetato‐κ4O:O,O′:O′]

The present form of barium acetate, formulated as [Ba(C₂H₃O₂)₂(H₂O)₃]_n, is the largest reported hydrate of the salt and this leads to a distinct structural behaviour setting it apart from the rest of the family. The compound is a linear polymer with a nine‐coordinate Ba(O_aqua)₃(O_acetate)₆ monomer unit. The non‐H part of the structure is ordered according to C2/m symmetry, while the disordered water H atoms only abide by this symmetry in a statistical sense. Each molecule is halved by a mirror plane bisecting the Ba centre, one water molecule and one acetate ligand, while containing the other acetate ligand. The chains are interconnected by a disordered water–water/acetate O—H...O hydrogen‐bonding network involving all water H atoms. The structure and stability of this phase are compared with the other known acetates of barium which differ in the degree of hydration.     

Dicalcium heptagermanate Ca2Ge7O16 revised

The structure of dicalcium heptagermanate, previously described with an orthorhombic space group, has been redetermined in the tetragonal space group . It contains three Ge positions (site symmetry 1, ..2 and 2.22, respectively), one Ca position (..2) and four O atoms, all on general 8i positions (site symmetry 1). A sheet of four‐membered rings of Ge tetrahedra (with Ge on the 8i position) and isolated Ge tetrahedra (Ge on the 4g position) alternate with a sheet of Ge octahedra (Ge on the 2d position) and eightfold‐coordinated Ca sites along the c direction in an ABABA… sequence. The three‐dimensional framework of Ge sites displays a channel‐like structure, evident in a projection on to the ab plane.     

Al6Ti2O13, a new phase in the Al2O3–TiO2 system

The compound Al₆Ti₂O₁₃ (hexa­aluminium dititanium trideca­oxide) has been synthesized using an arc‐imaging furnace, which allows fast cooling of melted oxides. The structure consists of infinite double chains of polyhedra running along the c axis. These chains are built up by four kinds of strongly distorted oxygen octa­hedra randomly occupied by either Ti or Al (point symmetry m or m2m), and by trigonal bipyramids exclusively occupied by Al (point symmetry m2m).     

Ca3GeO4Cl2 with a norbergite‐like structure

The title compound, tricalcium monogermanate dichloride, is orthorhombic and consists of one distinct Ge site on special position 4c, site symmetry m, and two different Ca sites, Ca1 and Ca2, one on general position 8d, site symmetry 1, and the other on special position 4c. Two of the O atoms occupy the 4c position (symmetry m); the third O atom is situated on the general 8d position, symmetry 1, as is the one distinct Cl position. By sharing common edges, the distorted Ca1 octahedra form infinite crankshaft‐like chains parallel to the b direction. Along a and c, these chains are connected to one another via common corners, thereby forming a three‐dimensional framework of edge‐ and corner‐sharing Ca1O₄Cl₂ octahedra. Triangular prisms of Ca2O₄Cl₂ polyhedra and GeO₄ tetrahedra fill the interstitial space within the Ca1 polyhedral framework. Relationships between the structures of the title compound and the humite‐type materials norbergite (Mg₃SiO₄F₂) and Mn₃SiO₄F₂ are discussed.     

catena‐Poly­[[bis­(hexa­fluoro­acetyl­acetonato‐κ2O,O′)­zinc(II)]‐μ‐4,4′‐bi­pyridine‐κ2N:N′]

The structure of the title compound, catena‐poly[[bis(1,1,1,5,5,5‐hexafluoropentane‐2,4‐dionato‐κ²O,O′)zinc(III)]‐μ‐4,4′‐bipyridine‐κ²N:N′], [Zn(C₅HF₆O₂)₂(C₁₀H₈N₂)]_n, con­sists of polymeric chains, running in two perpendicular directions, organized as planes normal to the tetragonal axis. The elemental unit of the chains is the zinc(II) coordination polyhedron bisected by a twofold symmetry axis, and thus only half of the unit is independent. The octahedral coordination geometry of the metal centre is composed of two oxy­gen‐chelating (symmetry‐related) hexa­fluoro­acetyl­acetonate groups and two translationally related 4,4′‐bi­pyridine groups, which act as connecting agents in the polymer structure. The stabilization of this architecture of chains and planes is associated with a number of weak C—H⋯O and C—H⋯F hydrogen bonds.     

Amide hydrogen bonding: control of the molecular and extended structures of two symmetrical pyridine‐2‐carboxamide derivatives

The crystal structures of two symmetrical pyridine‐2‐carboxamides, namely N,N′‐(propane‐1,3‐diyl)bis(pyridine‐2‐carboxamide), C₁₅H₁₆N₄O₂, (I), and N,N′‐(butane‐1,4‐diyl)bis(pyridine‐2‐carboxamide), C₁₆H₁₈N₄O₂, (II), exhibit extended hydrogen‐bonded sequences involving their amide groups. In (I), conventional bifurcated amide–carbonyl (N—H)...O hydrogen bonding favours the formation of one‐dimensional chains, the axes of which run parallel to [001]. Unconventional bifurcated pyridine–carbonyl C—H...O hydrogen bonding links adjacent one‐dimensional chains to form a `porous' three‐dimensional lattice with interconnected, yet unfilled, voids of 60.6 (2) ų which combine into channels that run parallel to, and include, [001]. 4% of the unit‐cell volume of (I) is vacant. Compound (II) adopts a Z‐shaped conformation with inversion symmetry, and exhibits an extended structure comprising one‐dimensional hydrogen‐bonded chains along [100] in which individual molecules are linked by complementary pairs of amide N—H...O hydrogen bonds. These hydrogen‐bonded chains interlock viaπ–π interactions between pyridine rings of neighbouring molecules to form sheets parallel with (010); each sheet is one Z‐shaped molecule thick and separated from the next sheet by the b‐axis dimension [7.2734 (4) Å].     

catena‐Poly[[[2‐(2‐chlorophenoxy)‐N′‐(2‐oxidobenzylidene‐κO)acetohydrazidato‐κ2N′,O]copper(II)]‐μ‐morpholine‐κ2N:O]

In the title compound, {[Cu(C₁₅H₁₁ClN₂O₃)(C₄H₉NO)]_n, the Cu^II cation has square‐pyramidal geometry. The morpholine ligand serves as a bridge to link two symmetry‐related metal atoms, resulting in an infinite chain structure along the a axis. Adjacent chains are extended into a two‐dimensional layered structure via hydrogen bonds formed between morpholine and amide N atoms [N—H...N = 2.971 (3) Å].