A new high‐pressure strontium germanate,SrGe2O5

The Sr–Ge–O system has an earth‐scientific importance as a potentially good low‐pressure analog of the Ca–Si–O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO₃ high‐pressure perovskite phase is the first Ge‐based transparent electronic conductor make the Sr–Ge–O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high‐pressure strontium germanate, SrGe₂O₅. Single crystals of this compound crystallized as a co‐existent phase with SrGeO₃ perovskite single crystals in the sample recovered in the compression experiment of SrGeO₃ pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium–oxygen framework layers stacked along [001], with Sr atoms located at the 12‐coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO₆ octahedra and between GeO₆ octahedra and GeO₄ tetrahedra. The present SrGe₂O₅ is thus isostructural with the high‐pressure phases of SrSi₂O₅ and BaGe₂O₅. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO₆ and GeO₄ polyhedra to cation substitution at the Sr site are much less than that of the SrO₁₂ cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.     

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.     

Chromium‐based clinopyroxene‐type germanates NaCrGe2O6 and LiCrGe2O6 at 298 K

The structure analyses of sodium chromium digermanate, NaCrGe₂O₆, (I), and lithium chromium digermanate, LiCrGe₂O₆, (II), provide important structural information for the clinopyroxene family, and form part of our ongoing studies on the phase transitions and magnetic properties of clinopyroxenes. (I) shows C2/c symmetry at 298 K, contains one Na, one Cr (both site symmetry 2 on special position 4e), one Ge and three O‐atom positions (on general positions 8f) and displays the well known clinopyroxene topology. The basic units of the structure of (I) are infinite zigzag chains of edge‐sharing Cr³⁺O₆ octahedra (M1 site), infinite chains of corner‐sharing GeO₄ tetrahedra, connected to the M1 chains by common corners, and Na sites occupying interstitial space. (II) was found to have P2₁/c symmetry at 298 K. The structure contains one Na, one Cr, two distinct Ge and six O‐atom positions, all on general positions 4e. The general topology of the structure of (II) is similar to that of (I); however, the loss of the twofold symmetry makes it possible for two distinct tetrahedral chains, having different conformation states, to exist. While sodium is (6+2)‐fold coordinated, lithium displays a pure sixfold coordination. Structural details are given and chemical comparison is made between silicate and germanate chromium‐based clinopyroxenes.     

Two‐dimensional square‐grid frameworks formed by self‐associating copper(II) complexes with 1‐(3‐pyridyl)‐ and 1‐(4‐pyridyl)‐substituted butane‐1,3‐diones

In bis­[1‐(3‐pyridyl)butane‐1,3‐dionato]copper(II) (the Cu atom occupies a centre of inversion), [Cu(C₉H₈NO₂)₂], (I), and bis­[1‐(4‐pyridyl)butane‐1,3‐dionato]copper(II) methanol solvate, [Cu(C₉H₈NO₂)₂]·CH₃OH, (II), the O,O′‐chelating diketonate ligands support square‐planar coordination of the metal ions [Cu—O = 1.948 (1)–1.965 (1) Å]. Weaker Cu⋯N inter­actions [2.405 (2)–2.499 (2) Å], at both axial sides, occur between symmetry‐related bis­(1‐pyridylbutane‐1,3‐dion­ato)copper(II) mol­ecules. This causes their self‐organization into two‐dimensional square‐grid frameworks, with uniform [6.48 Å for (I)] or alternating [4.72 and 6.66 Å for (II)] inter­layer separations. Guest methanol mol­ecules in (II) reside between the distal layers and form weak hydrogen bonds to coordinated O atoms [O⋯O = 3.018 (4) Å].     

Preparation,Structure, Spectral,and Magnetic Properties of Copper(II) Halogenonicotinates: Crystal and Molecular Structure of Tetrakis(μ‐2‐chloronicotinato‐O,O′)‐diaquadicopper(II)

The characterization of the complexes [Cu₂(2‐Clnic)₄(H₂O)₂] ( 1 ), [Cu(2,6‐Cl₂nic)₂(H₂O)₂] ( 2 ) and [Cu(5‐Brnic)₂(H₂O)₂]_n ( 3 ) (where 2‐Clnic = 2‐chloronicotinate, 2,6‐Cl₂nic = 2,6‐dichloronicotinate or 5‐Brnic = 5‐bromonicotinate) was based on elemental analysis, IR, electronic and EPR spectra, and magnetic susceptibility. Complex 1 was also studied by X‐ray analysis at 298 1a and 80 K 1b . The complex 1 contains a dinuclear Cu‐acetate molecular structure in which the carboxyl groups of the 2‐chloronicotinate ligands act as bridges and water molecules are at apical positions. The stereochemistry about Cu atom at both temperatures is typical for square pyramidal geometry with CuO₄O chromophore. The Cu‐Cu distance is 2.6513(8) and 2.6382(6) Å for 1a and 1b , respectively. The Cu atoms are displaced by 0.2069(9) and 0.1973(7) Å, respectively, from the plane containing four oxygen atoms bonded to the Cu atom toward the apical water molecules. Strong and weak hydrogen bonds as well as C–Cl···π interactions in the crystal structure are discussed as well. Both complexes, monomeric [Cu(2,6‐Cl₂nic)₂(H₂O)₂] ( 2 ) and polymeric [Cu(5‐Brnic)₂(H₂O)₂]_n ( 3 ), possess octahedral copper(II) stereochemistry with differing tetragonal distortions.     

Bi4Ge3O12 at the onset of pressure‐induced amorphization

The crystal structure of tetrabismuth tris(germanate), Bi₄Ge₃O₁₂ (I3d, Z = 4), is stable to at least 7.30 GPa, as demonstrated by hydrostatic single‐crystal X‐ray diffraction measurements in a diamond anvil cell at room temperature. The highest pressure reached in this study is close to the onset of amorphization at about 8 GPa. The Bi and Ge atoms are located at the 16c (3) and 12a () Wyckoff positions, respectively. The compression mainly affects the distorted BiO₆ octahedra, while the GeO₄ tetrahedra are relatively rigid. When compared with the values obtained under ambient conditions, the long Bi—O distances decrease with increasing pressure, while the short Bi—O distances do not change.     

Solid state electrochemical study of the phase diagram and thermodynamics of the ternary system CuGeO

Coulometric titrations using solid zirconia ionic conductors have been employed to determine the phase diagram of the ternary system CuGeO in the temperature range from 750 to 950°C. CuGeO₃ was found to be the only existing ternary compound in the system. It is in equilibrium with Cu₂O, CuO, GeO₂, and oxygen of atmospheric pressure. Cu and Cu₂O may coexist with GeO₂. The standard Gibbs energy of formation of CuGeO₃ was found to be ΔG°_f (CuGeO₃) = ?424.5 kJ/mole at 900°C. The standard enthalpy and entropy of formation are ΔH⁰_f = ?756.8 kJ/mole and ΔS°_f = ?283 J/mole·K, respectively.     

Kaliumamidotrioxogermanate(IV) – Wasserstoff-Brückenbindungen in K3GeO3NH2 und K3GeO3NH2 · KNH2

Potassium Amido Trioxo Germanates(IV) – Hydrogen Bridge Bonds in K₃GeO₃NH₂ and K₃GeO₃NH₂ · KNH₂ Colorless crystals of K₃GeO₃NH₂ and of K₃GeO₃NH₂ · KNH₂ were obtained by the reaction of KNH₂ with GeO₂ in supercritical ammonia at 450°C and p = 6 kbar in high-pressure autoclaves within 15 resp. 5 days. The crystal structures of both compounds were solved by X-ray single crystal methods. K₃GeO₃NH₂: P1 , a = 6.390(1) Å, b = 6.684(1) Å, c = 7.206(1) Å, α = 96.47(1)°, β = 101.66(1)°, γ = 91.66(1)°, Z = 2, R/R_w = 0.020/0.022, N(I) ≥ 2σ(I) = 3023, N(Var.) = 82 K₃GeO₃NH₂ · KNH₂: P2₁/c, a = 10.982(6) Å, b = 6.429(1) Å, c = 12.256(8) Å, β = 106.12(1)°, Z = 4, R/R_w = 0.022/0.029, N(F) ≥ 3σ(F) = 1745, N(Var.) = 107. In K₃GeO₃NH₂ tetrahedral ions GeO₃NH₂^3? are connected to chains by N? H …? O bridge bonds with 2.18 Å ≤ d(H …? O) ≤ 2.40 Å for d(N? H) ? 1.0 Å and by potassium ions while in K₃GeO₃NH₂ · KNH₂ bridge bonds between NH₂ groups of GeO₃NH₂^3? and NH₂^? ions as acceptors occur with 2.41 Å ≤ d((N? )H …? NH₂^?) ≤ 2.61 Å for d(N? H) ? 1.0 Å.     

TlCu5O(VO4)3 mit KCu5O(VO4)3‐Struktur – ein Thallium‐kupfer(II)‐oxidvanadat als Oxidationsprodukt einer Tl/Cu/V‐Legierung

TlCu₅O(VO₄)₃ with KCu₅O(VO₄)₃ Structure – a Thallium Copper(II) Oxide Vanadate as an Oxidation Product of a Tl/Cu/V Alloy Brown‐black crystals of the new oxide vanadate TlCu₅O(VO₄)₃ (triclinic, P1, a = 610.4(1) pm, b = 828.9(1) pm, c = 1075.3(1) pm, α = 97.70(1)°, β = 92.25(1)°, γ = 90.28(1)°, Z = 2) were obtained as a byproduct during the reaction of a Tl/Cu/V alloy with oxygen. The compound is isotypic with KCu₅O(VO₄)₃. All the crystals investigated were twins by non‐merohedry with [100] as the twin axis. The structure contains ladder shaped [Cu₁₀O₂₆]‐ribbons composed of edge‐ and corner‐sharing [CuO₅]‐polyhedra (tetragonal pyramids and trigonal bipyramids) and linked by vanadate groups. The thallium ions fill channels running along the a axis. No stereochemical activity of the thallium(I)‐lone pair is observed.     

Neue Beobachtungen zum chemischen Transport von GeO2 II. Transportmittel Wasserstoff

Novel Observations on the Chemical Transport of GeO₂. II. Transport Agent Hydrogen The endothermic reaction (1) (2) is the basis of the deposition of GeO₂ in the temperature gradient T₂ ? T₁ = 100 K at the low temperature T₁ = 1023 K. The quartz modification of GeO₂ is obtained as micro crystalline coating and acicular, colourless crystals adherent to it. The gaseous molecules H₂, H₂O and (GeO)_n (with n = 1, 2, 3) participate in the chemical transport. The chemical transport depends on the concentration of H₂. At low H₂-concentration GeO₂ is transported, with growing H₂-pressure at the beginning of the experiments Ge and GeO₂ are deposited simultaneously. A further increase of the H₂-pressure leads again to a chemical transport of GeO₂, followed by a range of Ge-deposition. After reaching a steady state in each experiment only one phase is transported. The sequence of deposition can be explained by model calculations. A comparison of experimentally determined rates of transport with calculated values shows that under the present conditions at a total pressure of ∑P = 1 atm (298 K) no kinetic inhibition of the phase transfer reactions exists.     

Non‐Isomorphic Chlorine—Bromine Substitution in the Copper(I) Halide π‐Complexes with 1‐Allyl‐4‐aminopyridinium

By alternating‐current electrochemical synthesis crystals of {Cu[H₂NC₅H₄N(C₃H₅)]Br₂} ˙ H₂O ( I ), {Cu[H₂NC₅H₄N(C₃H₅)]Br_0.65Cl_1.35} ˙ H₂O ( II ) and {Cu[H₂NC₅H₄N(C₃H₅)]Cl₂} ( III ) π‐complexes have been obtained and structurally investigated. The I and II compounds are isostructural and crystallize in a monoclinic sp. gr. P2₁/c, I : a = 7.359(2)Å, b = 12.3880(6)Å, c = 13.637(3)Å, β = 107.03(1)°, V = 1188.7(4)ų, Z = 4 for C₈H₁₃N₂OBr₂Cu composition, R = 0.0293 for 2140 reflections. II : a = 7.2771(6)Å, b = 12.3338(3)Å, c = 13.4366(7)Å, β = 107.632(2)°, V = 1149.3(1)ų, Z = 4 for C₈H₁₃N₂Br_0.65Cl_1.35Cu composition, R = 0.0463 for 2185 reflections. Metal and halogen atoms form centrosymmetric Cu₂X₄ dimers. Each copper atom is surrounded by three halogen atoms and by a weakly bonded C=C‐group of the onium moiety. Isolated {Cu[H₂NC₅H₄N(C₃H₅)]}₂X₄ dimers are combined into a three‐dimensional network due to a bridging function of water molecules via a system of rather strong hydrogen bonds. Chlorine derivative III crystallizes in another structure type: sp. gr. C2/c, a = 21.568(7)Å, b = 7.260(2)Å, c = 13.331(3)Å, β = 95.65(2)°, V = 2077(2)ų, Z = 8 for C₈H₁₁N₂Cl₂Cu composition. Copper atom, included in CuCl₂^— isolated fragment, is coordinated to a C=C‐bond of ligand moiety. N‐H…Cl hydrogen bonds unite Cu[H₂NC₅H₄N(C₃H₅)]Cl₂ subunits into infinite ribbons. π‐Interaction in III appears to be more effective than in I and II .     

Bis(hinokitiolato)copper(II): modification (III)

Bis(hinokitiolato)copper(II), Cu(hino)₂, exhibits both antibacterial and antiviral properties, and has been previously shown to exist in two modifications. A third modification has now been confirmed, namely tetrakis(μ₂‐3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trien‐1‐olato)bis(3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trien‐1‐olato)tricopper(II)–bis(μ₂‐3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trien‐1‐olato)bis[(3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trien‐1‐olato)copper(II)] (1/1), [Cu(C₁₀H₁₁O₂)₂]₃·[Cu(C₁₀H₁₁O₂)₂]₂, where 3‐isopropyl‐7‐oxocyclohepta‐1,3,5‐trien‐1‐olate is the systematic name for the hinokitiolate anion. This new modification is composed of discrete [cis‐Cu(hino)₂]₂[trans‐Cu(hino)₂] trimers and [cis‐Cu(hino)₂]₂ dimers. The Cu atoms are bridged by μ₂‐O atoms from the hinokitiolate ligands to give distorted square‐pyramidal and distorted octahedral Cu^II coordination environments. Hence, the Cu^II environments are CuO₅/CuO₆/CuO₅ for the trimer and CuO₅/CuO₅ for the dimer. Each trimer and dimer has crystallographically imposed inversion symmetry. The trimer has never been observed before, the dimer has been seen only once before, and the combination of the two together in the same lattice is unprecedented. The CuO₅ cores exhibit four strong basal Cu—O bonds [1.915 (2)–1.931 (2) Å] and one weak apical Cu—O bond [2.652 (2)–2.658 (2) Å]. The CuO₆ core exhibits four strong equatorial Cu—O bonds [1.922 (2)–1.929 (2) Å] and two very weak axial Cu—O bonds [2.911 (3) Å]. The bite angles for the chelating hinokitiolate ligands range from 83.13 (11) to 83.90 (10)°.     

A three‐dimensional supramolecular network built with the zigzag chain complex bis(5‐carboxy‐1H‐imidazole‐4‐carboxyl­ato)copper(II)

In the title complex, poly[copper(II)‐di‐μ‐5‐carboxy‐1H‐imidazole‐4‐carboxyl­ato], [Cu(C₅H₃N₂O₄)₂]_n or [Cu(H₂Imda)₂]_n, each imidazole moiety is bonded to the Cu atom via O and N atoms to give a square‐planar coordination [Cu—O = 2.014 (2) and 2.016 (2) Å, and Cu—N = 1.982 (3) and 1.992 (2) Å]. The distorted square‐pyramidal geometry at the Cu atom results from coordination to an adjacent O atom [Cu—O = 2.305 (2) Å], which generates zigzag chains. There is a sixth, weaker, octahedral coordination to the Cu atom from an inversion‐related O atom [Cu—O = 3.090 (2) Å], which links the chains into sheets in the (100) plane. Imidazole moieties in the sheets are linked in the [100] direction by pairs of N—H⋯O and C—H⋯O hydrogen bonds, thus generating a three‐dimensional network.     

Zur Kristallstruktur von CuGeO3

The crystal structure of CuGeO₃ (D _2h ⁵ -Pbmm) has been redetermined by means of 3-dimensional Fourier syntheses. The structure is built up by [CuO₄]- and [GeO₃]-chains (Einereinfachkette). The interatomic distances are found to be: Ge?O: 1,76₉ (2x) and 1,72₄ (2x) Å; Cu?O: 1,94₂ (4x) and 2,76₆ (2x) Å.     

Synthesis and Crystal Structures of Nickel(II) and Copper(II) Complexes of Meso-3,6,6,9-Tetramethyl-4,8-Diazaundecane-2,10-Dione Dioxime

The nickel(II) and copper(II) complexes of meso-3,6,6,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (meso-HM-PAO) have an intramolecular hydrogen bond between cis oxime groups. [Cu(meso-HM-PAO-H)(H₂O)](NCS) crystallizes in space group P2₁/n with a = 7.692(1), b = 12.028(2), c=20.235(3) Å, β=93.03(1)°, Z = 4 and Dc=1.46 g/cm³. The final R value for this complex was 0.034 for 2223 observed reflections with I ≥ 2.5σ (I). The Cu(II) coordination is a distorted square pyramid. The Cu(II) ion is five-coorinated with the diazadioxime N atoms equatorial and water O atom axial. The Cu(II) is 0.12 Å from the equatorial plane towards the hydrate. The equatorial Cu-N distances span a narrow range, 1.953(3)-1.999(3) Å. The axial Cu-O distance is 2.314(3) Å. The thiocyanate group is almost linear. The intramolecular O ?O hydrogen bond length is 2.479(4) Å. [Ni(meso-HM-PAO-H)](ClO₄) crystallizes in space group P2₁/c with a = 14.774(3), b = 12.752(3), c = 20.035(4) Å, β = 92.94(3)°, Z = 8 and Dc = 1.51 g/cm³. The final R value for the complex was 0.053 for 4794 observed reflections with F ≥ 4σ (F). The coordination about Ni(II) is a slightly distorted square plane. The Ni(II) ion is 0.0673(7) Å from the best plane of the four donor nitrogen atoms away from the perchlorate ion. The Ni-N distances span a narrow range 1.863(4)-1.927(4) Å. There are two molecules per asymmetrical unit resulting in eight molecules being packed in an unit cell; they are bound together by van der Waals interactions. The O-H ?O bonds of these complexes give characteristic infrared absorptions as well as chemical shift of the ¹H NMR signal (Ni complex).     

A new binuclear germanium(IV) and copper(II) complex with 1,3-diamino-2-propanoltetraacetic acid: Crystal and molecular structure of [(H2O)(OH)Ge(μ-Hpdta)Cu(H2O)] · 3H2O

A heteronuclear germanium(IV) and copper(II) complex with 1,3-diamino-2-propanoltetraacetic acid (H₅Hpdta) has been synthesized for the first time. The compound has been characterized by elemental analysis, X-ray diffraction, thermogravimetry, and IR spectroscopy. The structure of the complex [(H₂O)(OH)Ge(μ-Hpdta)Cu(H₂O)] · 3H₂O (I) has been determined by single-crystal X-ray diffraction. The crystals of I are monoclinic, a = 1 5.327(4) Å, b = 11.626(3) Å, c =21.058(3) Å, β = 96.35(2)°, V = 3729.2(2) ų, Z = 8, space group C2/c, R1 = 0.0551 on 3090 reflections with I > 2σ(I). The structural units of the crystal of I are binuclear complex molecules [(H₂O)(OH)Ge(μ-Hpdta)Cu(H₂O)] and crystal water molecules. The germanium and copper atoms are linked by the bridging oxygen atom of the deprotonated isopropanol group of the Hpdta^5? ligand (Ge-O, 1.843(3) Å; Cu-O, 2.221(3) Å). The coordination spheres of the Ge and Cu atoms contain each one nitrogen atom (Ge-N, 2.090(4) Å; Cu-N, 2.000(4) Å) and two carboxyl oxygen atoms from four acetate arms of the heptadentate Hpdta^5? ligand (av. Ge-O, 1.909(3) Å; Cu-O, 1.948(3) Å). The coordination polyhedron of the Ge atom is completed to a distorted octahedron by the oxygen atoms of the terminal hydroxy group (Ge-O, 1.786(3) Å) and a water molecule (Ge-O, 1.904(3)Å). The coordination polyhedron of the copper atom is completed to a prolate tetragonal pyramid (4 + 1) by the oxygen atom of a water molecule in the equatorial position (Cu-O, 1.955(4) Å) and the bridging O(11) atom (Hpdta^5?) in the apical position. Binuclear molecules are linked pairwise in a head-to-head manner via double Cu-O(2) bridges to form the centrosymmetric tetranuclear supramolecule {[(H₂O)(OH)Ge(μ-Hpdta)Cu(H₂O)]}₂. The coordination of the Cu atom is completed by the weak Cu-O(2A) contact (3.303 Å) to an asymmetrically elongated tetragonal bipyramid (4 + 1 +1). In the crystal, the complex molecules and crystal water molecules are combined by a system of hydrogen bonds into a three-dimensional framework.     

FeII2(PO4)(OH), a synthetic analogue of wolfeite

This paper reports the hydrothermal synthesis and crystal structure refinement of diiron(II) phosphate hydroxide, Fe^II₂(PO₄)(OH), obtained at 1063 K and 2.5 GPa. This phosphate is the synthetic analogue of the mineral wolfeite, and has a crystal structure topologically identical to those of minerals of the triplite–triploidite group. The complex framework contains edge‐ and corner‐sharing FeO₄(OH) and FeO₄(OH)₂ polyhedra, linked via corner‐sharing to the PO₄ tetrahedra (average P—O distances are between 1.537 and 1.544 Å). Four five‐coordinated Fe sites are at the centers of distorted trigonal bipyramids (average Fe—O distances are between 2.070 and 2.105 Å), whereas the coordination environments of the remaining Fe sites are distorted octahedra (average Fe—O distances are between 2.146 and 2.180 Å). The Fe—O distances are similar to those observed in natural Mg‐rich wolfeite, except for two Fe—O bond distances, which are significantly longer in synthetic Fe²⁺₂(PO₄)(OH).     

High‐Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus

Titanium(III) phosphate, TiPO₄ , is a typical example of an oxyphosphorus compound containing covalent P?O bonds. Single‐crystal X‐ray diffraction studies of TiPO₄ reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high‐pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO₄‐V is the first inorganic phosphorus‐containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO₄‐V coexists with TiPO₄‐IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO₄‐II is found to be an incommensurately modulated phase whereas a lock‐in transition at about 7 GPa leads to TiPO₄‐III with a fourfold superstructure compared to the structure of TiPO₄‐I at ambient conditions. TiPO₄‐II and TiPO₄‐III are similar to the corresponding low‐temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin‐Peierls interactions.     

Rietveld Analysis of a High Pressure Modification of Monocalcium Oxogallate (CaGa2O4)

A high‐pressure modification of monocalcium gallate (CaGa₂O₄) has been prepared in a piston‐cylinder apparatus at 700 °C and 4.0 GPa. The compound is orthorhombic (space group Pnam, a = 9.12476(15) Å, b = 10.56093(18) Å, c = 2.98547(4) Å, V = 287.70(1) ų, Z = 4, D_calc = 5.62 g/cm³) and belongs to the CaFe₂O₄‐type structure family. The structure was refined by the Rietveld method using laboratory X‐ray powder diffraction data. Two crystallographically independent GaO₆‐octahedra forming edge‐sharing double chains can be distinguished. The shared edges exhibit a considerable shortening. The chains are running parallel to the c‐axis and are linked by corner‐sharing. They enclose tunnels in which the calcium atoms are located for charge compensation. Each calcium cation has eight nearest oxygen neighbors. The coordination environment can be described as a bicapped trigonal prism.     

(C5H14N2)[Zn3(HPO4)4], a New 3D Open‐framework Zincophosphate Synthesized by Hydrothermal Reversible Transformation of (C5H14N2)[Zn2(HPO4)3]·H2O

In the system ZnO/H₃PO₄/H₂O/1,4‐diazacycloheptane (C₅H₁₂N₂), a new zincophosphate (ZnPO), (C₅H₁₄N₂)[Zn₃(HPO₄)₄] ( I ), was prepared by hydrothermal transformation (180 °C) of the known ZnPO hydrate (C₅H₁₄N₂)[Zn₂(HPO₄)₃]·H₂O ( II ). The thermally‐induced transformation is reversible; upon keeping the heterogeneous mixture of I and mother liquor at 80 °C recrystallization of II was observed. Single‐crystal X‐ray crystallography revealed that I possesses a unique three‐dimensional (3D) open‐framework structure built from corner‐linked ZnO₄ and HPO₄ tetrahedra. The (3,4)‐connected framework of I differs considerably from the 3D open‐framework ZnPO structure of II . Crystal data for I : Monoclinic system, space group Cc (No. 9) , Z = 4, a = 9.1389(6), b = 23.627(2), c = 9.3073(6) Å, β = 109.463(7)°, T = 298 K.