The crystal structure of LaIr4B4, ThOs4B4, ThIr4B4 (NdCo4B4-type) and URu4B4, UOs4B4 (LuRu4B4-type)

The crystal structure of LaIr₄B₄ has been refined from single crystal counter data. LaIr₄B₄ is tetragonal,P4₂/n,Z=2, isotypic with NdCo₄B₄, |F|/|F _o|=0.039 for 312 independent reflections [|F _o|>2 (F _o)]. ThIr₄B₄ and ThOs₄B₄ also belong to the NdCo₄B₄-type structure. URu₄B₄ and UOs₄B₄ were found to crystallize with LuRu₄B₄-type structure. The crystal chemistry of (RE)T ₄B₄-phases is discussed and simple geometric relations are shown to exist between them.Dedicated to Prof.B. T. Matthias in celebration of his 60th birthday.     

Studies on Li2SO4-MgSO4 and Li2SO4-Li4SiO4 systems

The phase equilibria as well as the properties and crystal structures of the compounds formed in both Li₂SO₄-MgSO₄ and Li₂SO₄-Li₄SiO₄ systems have been studied by means of x-ray diffraction technique (at high and room temperatures) as well as by the thermal analyses (DTA, DSC, TGA, etc.). In Li₂SO₄-MgSO₄ system there exists a compound Mg₄Li₂(SO₄)₅ formed by peritectic reaction at 840°C and decomposed at 105°C into the Li₂SO₄-base solid solution and MgSO₄ · Mg₄Li₂(SO₄)₅ and Li₂SO₄-base solid solution conduct an eutectic reaction at 663°C with the composition of eutectic point lying in 22 mol% MgSO₄. The solubility of MgSO₄ in Li₂SO₄ is a little smaller than 10 mol% while at the same time the Li₂SO₄ phase transition temperature decreases from 574 to 560°C On the other hand, no noticeable solid solubility of Li₂SO₄ in MgSO₄ has been observed. The reaction is an endothermal one and its heat of formation is 2.57 kJ/mol. The activation energy of the reaction calculated by thermal peak displacement method at various heating rates is 173.5 kJ/mol (1.80 ev). The crystal Mg₄Li₂(SO₄)₅ belongs to orthorhombic system with lattice parameters at 180°C: a = 8.577, b=8.741, c= 11.918 Å. The space group seems to be either P222 or P mmm. Assuming that there are two formula units in a unit cell, the density calculated is then 2.20 g/cm³ very close to that of Li₂SO₄ or MgSO₄. Meanwhile, in Li₂SO₄-Li₄SiO₄ system a new phase Li_8-2x(SiO₄)_8-x(SO₄)_x is formed by peritectic reaction at 953°C with a range of composition x=0.96 ?0.58. The crystal belongs to ortho-rhombic system with lattice parameters at x=0.8: a = 5.002, b= 6.173 and c=10.608Å. The density observed is 2.31 g/cm³ and there are 2 formula units in an unit cell. It is shown from the measurements of piezoelectric and laser SHG coefficients of the crystal that the crystal posseses a symmetrical center with the space group belonging to P mmn. The lattice parameter c has a maximum at x=0.8. In the air Li_8-2x(SiO₄)_2-x(SO₄)_x can absorb 7.6 wt% water vapour and other gases which can only be desorbed by heating it at a temperature above 350°C. Neither absorption nor desorbtion can change its crystal structure, a characteristic similar to that of zeolite molecular sieve. The dewater activation energy of Li_8-2x(SiO₄)_2-x(SO₄)_x is 171.5 kJ/mol. Li_8-2x(SiO₄)_2-x(SO₄)_x and Li₄SO₄ bring about an eutectic reaction at 823°C with its eutectic composition being 12 mol% Li₄SiO₄. No observable solubility of Li₄SiO₄ in Li₃SO₄ has been noticed. The solubility of Li₂SO₄ in Li₄SiO₄ is approximately equal to 5 mol%. With Li₂SO₄ being dissolved in, the phase transition temperature of Li₄SiO₄ is decreased. After being fused, the specimens Li₃SO₄-MgSO₄ and Li₂SO₄-Li₄SiO₄ are cooled at a rate of 10°C/min, their metastable eutectic systems are resulted respectively.     

Schwingungsspektren von As4S4 und As4Se4

Vibrational Spectra of As₄S₄ and As₄Se₄ The vibrational spectra of solid α- and β-As₄S₄ and the Raman spectrum of molten As₄S₄ have been recorded. The assignments of the frequencies are proposed mainly based on polarization data. The Raman melt spectra suggest that As₄S₄ molecules (symmetry D_2d) are retained in the molten state. A partial decomposition of the melt by prolonged laser irradiation was observed. The Raman spectrum of solid As₄Se₄ is presented and the frequencies are tentatively assigned to an As₄Se₄ molecule of the cradle type, possessing D_2d symmetry.     

Neues vom P4Se4

New Results on P₄Se₄ Preparation of P₄Se₄ from the elements yields always the β-modification of P₄Se₄. α-P₄Se₄ is obtained only with selenium deficient samples. However, it is also observed, when P₄Se₃ is annealed and then extracted with CS₂. The insoluble part has the X-ray pattern of α-P₄Se₄. A reversible α-β transition is not observed. MAS-³¹P-NMR investigations on solid P₄Se₄ by Eckert et al. [2] reveal P₂Se_4/2 building units, which are, in view of our results, not dimer but linked to a polymeric network. Well-crystallized samples of β-P₄Se₄ are obtained only at measuring temperatures above 573 K. The structure is of monoclinic symmetry with the space group P2₁/n (a = 114.9, b = 729.0, c = 1211.0 pm, β = 120.80°). The reaction of α-P₄Se₃I₂ with bis-(trimethyltin)selenide in CS₂ at low temperature yields molecular α-P₄Se₄, which can be detected in solution by ³¹P-NMR spectroscopy. α-P₄Se₄ has D_2d-symmetry like α-P₄S₄. It polymerizes at higher temperature. α-P₄Se₃I(SeSnMe₃) and α-P₄Se₃(SeSnMe₃)₂ were observed in the course of this reaction, too. The analogous reaction of α-P₄Se₃I₂ with bis-(trimethyltin)sulfide leads to comparable results.     

K4PbO4 und K4GeO4 – ein Vergleich

K₄PbO₄ and K₄GeO₄ — a Comparison The question is: In which case are two compounds isotypic? The structures of K₄PbO₄ and K₄GeO₄ are derived using ?Schlegelprojektionen”? (reduced atomic distances and angles) and ?Erweiterte Schlegeldiagramme”? of the anions: O1, O2, O3 and O4. The difference is pointed out and discussed. For both compounds the interatomic distances are listed.     

Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

Zintlphasen mit isolierten SiAs4- bzw. GeAs4-Anionen: Darstellung und Struktur von Ba4SiAs4 und Ba4GeAs4 sowie Sr4SiAs4 und Sr4GeAs4

Die erstmals dargestellten isotypen Verbindungen Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄ und Sr₄GeAs₄ kristallisieren kubisch, Raumgruppe P4 3n, mit 8 Formeleinheiten in der Elementarzelle: In den Strukturen liegen isolierte, d.h. nur von Ba-Ionen umgebene SiAs - bzw. GeAs -Tetraeder vor. Die Verbindungen sind die bisher eindrucksvollsten Beispiele für Zintlphasen mit komplexen Anionen. Zintl Phases with Isolated SiAs₄ or GeAs₄ Anions: Preparation and Structure of Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄, and Sr₄GeAs₄ The new compounds Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄, and Sr₄GeAs₄ have been prepared and their structures determined. They crystallize in the cubic system, P4 3n, with axes: data see “Inhaltsübersicht”. There are isolated SiAs or GeAs tetrahedra in the structures. The compounds can be interpreted as Zintl phases with complex anions.     

Syntheses and Structures of S4N4(OCH3)2 and CH3OS4N4(O)Cl

The reaction of S₄N₄Cl₂ with CH₃OH gives S₄N₄(OCH₃)₂, a simple dimethoxoderivative of S₄N₄. Its overall geometry is analogous to other compounds of the S₄N₄X₂ type. The chlorination of S₄N₄(OCH₃)₂ leads to the oxidation of one sulfur atom to S^VI and CH₃OS₄N₄(O)Cl is formed. The compounds were characterized by ir spectroscopy and their crystal structures were determined from single crystal diffraction data collected at ?153°C. The presence of S^VI in the molecule of CH₃OS₄N₄(O)Cl is manifested by a marked shortening of the bonds formed by this atom as compared with S₄N₄Cl₂ and S₄N₄(OCH₃)₂.     

Zur Kenntnis von K4PbO4 und Rb4PbO4

On K₄PbO₄ and Rb₄PbO₄ For the first time single crystals of K₄[PbO₄] have been prepared by heating K₄PbO₃ in O₂. The structure has been refined [K₄[PbO₄]: 3029 I₀(hkl), four circle diffractometer PW 1100, ω-scan, MoKα, R = 6.73%, R_w = 6.64%, P1 ; a = 658.62(15), b = 658.41(12), c = 986.64(21) pm, α = 79.74(2)°, β = 108.45(2)°, γ = 112.49(2)°, d_x = 3.79 g · cm^?3, d_pyk = 3.78 g · cm^?3, Z = 2; Rb₄[PbO₄]: a = 686.94(18), b = 684.43(18), c = 1020.73(21) pm, α = 79.28(2)°, β = 108.40(2)°, γ = 113.02(2)°, d_x = 4.87 g · cm^?3, d_pyk = 4.85 g · cm^?3, Z = 2, (from Rb₂PbO₃ and Rb₂O)]. Both compounds are isotypic with K₄SnO₄. The Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated.     

Darstellung und Struktur von Ag2C4O4

Preparation and Structure of Ag₂C₄O₄ Ag₂C₄O₄ occurs in a yellow and a colourless modification. Both forms decompose to metallic silver upon heating. Ag⁺ is coordinated in two different fashions in the yellow Ag₂C₄O₄. Ag(1) shows distorted tetrahedral coordination, Ag(2) is coordinated in an unusual distorted square planar manner. The connection of Ag⁺ and C₄O₄^2? leads to a complicated three-dimensional framework. C₄O₄^2? is planar with C? O and C? C bonds lengths typical of complete delocalization of the π-electron system.     

Zur Kenntnis der K4[Ag4O4]-Verwandtschaft

On the K₄[Ag₄O₄] Relation Single crystals of mainly new oxides A₄[M₄O₄] with M = Cu, A = Li? Rb and M = Ag, A = Na, Rb, Cs have been prepared by “reaction at the metallic substrate” (i.e. the wall) and the crystal structures were refined. For lattice constants and atomic parameters see text. The [M₄O₄]^4? ring is planar only for the M₄-part, the positions of the O^2? particles deviate in a non systematic way from this plane. Only Li₄[Cu₄O₄] contains an almost planar ring. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated.     

Statistische Modellrechnungen an den Molekülen CH4, SiH4, GeH4, SnH4 und PbH4 nach der Einzentrenmethode

Zusammenfassung Mit einem Einzentren-Ansatz werden Bindungsabstände und Gesamtenergien der Moleküle CH₄, SiH₄, GeH₄, SnH₄ und PbH₄ berechnet. Die statistische Betrachtungsweise der Elektronen nach Gombás und Ladányi [1] wird mit der Edelgas-Modellvorstellung nach Hartmann und Gliemann [2] verknüpft. Die Ergebnisse liegen in guter Übereinstimmung mit den vorliegenden experimentellen Daten. Bindungsabstand und Gesamtenergie des Moleküls PbH₄ werden erstmals berechnet.

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Statistical OCE-calculations on the molecules CH₄, SiH₄, GeH₄, SnH₄ and PbH₄

OCE-calculations are reported for ground state energies and bond distances of the hydrides CH₄, SiH₄, GeH₄, SnH₄ and PbH₄. The statistical atom model (Gombás and Ladányi [1]) is connected with the noble gas model (Hartmann and Gliemann [2]). The results are in good agreement with known experimental values. Bond distance and ground state energy of PbH₄ are presented for the first time.

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Wir danken der DFG für die finanzielle Unterstützung dieser Arbeit.     

Synthese,Eigenschaften und Struktur von LiAuI4 und KAuI4 mit einer Diskussion der kristallchemischen Verwandtschaft zwischen den Halogenoauraten RbAuCl4, AgAuCl4, RbAuBr4 und LiAuI4

Synthesis, Properties, and Structure of LiAuI₄ and KAuI₄ with a Discussion of the Crystal Chemical Relationship between the Halogenoaurates RbAuCl₄, AgAuCl₄, RbAuBr₄ and LiAuI₄ The alkalimetal iodo aurates(III) MAuI₄ (M ? Li, K) are obtained in form of single crystals from MI, Au and I₂ in a sealed glass ampoule by heating to 550°C and slow cooling to 300°C. KAuI₄ crystallizes in the monoclinic space group P2₁/c with a = 968.6(4); b = 704.5(2), c = 1393.2(7) pm; β = 100.95(2)° and Z = 4. The crystal structure is built up from square planar AuI₄^? anions and K⁺ cations. The cations are coordinated by eight I atoms of neighbouring AuI₄^? anions with distances K? I between 350.0 and 369.6 pm. At 100°C KAuI₄ is reduced to form K₃Au₃I₈, which at 180°C decomposes to KI, Au and I₂ LiAuI₄ forms black, moisture sensitive needles, decomposing in the absence of iodine at 20°C to LiI, Au and I₂. It crystallizes in a variant of the RbAuBr₄ type structure with the space group P2₁/a and a = 1511.7(4); b = 433.9(4); c = 710.0(2) pm; β = 121.50(2)°; Z = 2. The crystal chemical relationship between the structures of RbAuCl₄, RbAuBr₄, AgAuCl₄ and LiAuI₄ is discussed.     

Die K4[Ag4O4] — Strukturfamilie

K₄[Ag₄0₄] Structure Type M₄[Ag₄O₄] (M ? Li? Cs) and M₄[Cu₄O₄] (M ? Li? Rb) have been prepared anew; as an example the crystal structure of K₄[Ag₄O₄] has been revised. Contrary to our first report [2, 3] it crystallizes in the space-group I4 m2 with the “ring” [Ag₄O₄]^4? which is not plane, however. Each two O^2? (trans-arrangement) are rather (0.02 Å) above and below the plane of the “ring”, respectively. The new parameters are given in the text. The distances, for example d(Ag⁺·O^2?) = 2.058 Å and the Madelung Part of Lattice Energy, MAPLE, are both in a very good agreement with the measurements and calculations, respectively, which have been done on other ternary oxides with silver.     

Comparison of the crystal structures of sodium orthosilicate,Na4SiO4, and sodium orthogermanate,Na4GeO4

The crystal structures of Na₄SiO₄ and Na₄GeO₄ are isotypic, despite a difference in coordination numbers: in Na₄SiO₄ only one of the four symmetrically independent sodium atoms is four coordinated, in Na₄GeO₄ two of them are.

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Vergleich der Kristallstrukturen von Natriumorthosilikat, Na₄SiO₄, und Natriumorthogermanat, Na₄GeO₄ (Kurze Mitteilung)

Zusammenfassung Die Kristallstrukturen von Na₄SiO₄ und Na₄GeO₄ sind isotyp, trotz eines Unterschiedes in den Koordinationszahlen: im Na₄SiO₄ ist nur eines der symmetrisch unabhängigen Natriumatome vierfach koordiniert, während es im Na₄GeO₄ derer zwei sind.

     

Raman spectroscopic study of aqueous (NH4)2SO4 and ZnSO4 solutions

The Raman spectra of the v₁-SO ₄ ^2– band in 0.5–2.5 molar aqueous (NH₄)₂SO₄ and ZnSO₄ solutions in the temperature range 25–85°C were studied. The molar scattering coefficient of the v₁ band is the same for all forms of sulfate in (NH₄)₂SO₄ and ZnSO₄ solutions and is independent of temperature up to 85°C. The v₁ band profile is symmetrical in (NH₄)₂SO₄ solutions. In ZnSO₄ solutions, a shoulder appears on the high frequency side which increases slightly in intensity with increasing concentration and temperature. This high frequency component is attributed to the formation of the contact ion pair (Zn²⁺·SO ₄ ^2– ). The enthalpy of formation for the contact ion pair is estimated from the Raman data to be approximately 3 kJ-mol^–1 which is in reasonable agreement with measurements by other methods.     

Halogenide der Seltenerdmetalle Ln4X5Z. Teil 3: Das Chlorid La4Cl5B4 – Präparation,Struktur und Verwandtschaft zu La4Br5B4, La4I5B4

Rare Earth Halides Ln₄X₅Z. Part 3: The Chloride La₄Cl₅B₄ – Preparation, Structure, and Relation to La₄Br₅B₄, La₄I₅B₄ La₄Cl₅B₄ is synthesized by reaction of LaCl₃, La metal and boron in sealed Ta containers at 1050 °C < T < 1350 °C. It crystallizes in the monoclinic space group C2/m with a = 16.484(3) Å, b = 4.263(1) Å, c = 9.276(2) Å and β = 120.06(3)°. Ce₄Cl₅B₄ is isotypic, a = 16.391(3) Å, b = 4.251(1) Å, c = 9.180(2) Å and β = 120.20(3)°. The La atoms form strings of trans-edge shared La octahedra, and the B atoms inside the strings form B₄-rhomboids, which are condensed to chains via opposite corners. The Cl atoms interconnect the channels according to La₂La_4/2Clⁱ⁻ⁱ_6/2Cl^i−a_2/2Cl^a−i_2/2. The crystal structures of the bromide and the iodide are comparabel, however, the interconnection of the strings is different in the three structure types, as 14 Cl, 13 Br and 12 I atoms surround the La₆ octahedra.     

S4N4 und seine Derivate: β-FeCl3 · S4N4, ein Übergangsmetallkomplex mit dem S4N4-Ligand

S₄N₄ and its Derivatives: β-FeCl₃ · S₄N₄, a Transition Metal Complex with the S₄N₄ Ligand The reaction of FeCl₃ with S₄N₄ in CCl₄ yields among other products two modifications of FeCl₃ · S₄N₄. The β-modification crystallizes in the monoclinic space group P2₁/c with Z = 4 and the lattice parameters a = 6.803(3), b = 11.312(4), c = 13.784(5) Å and β 95.02(3)º. An X-ray analysis shows that the S₄N₄ ligand is bonded via one of its N atoms and completes the coordination tetrahedron around the Fe atom, like in the α-modification investigated earlier.     

Cu4O12-Baugruppen aus planaren CuO4-Polygonen im Barium-Vanadyl-Oxocuprat(II)-phosphat Ba(VO)Cu4(PO4)4

Cu₄O₁₂ Groups Built of Square Planar CuO₄ Polygones in the Barium Vanadyl Oxocuprate(II) Phosphate Ba(VO)Cu₄(PO₄)₄ Single crystals of Ba(VO)Cu₄(PO₄)₄ have been prepared by solid state reactions just below the melting points of the reaction mixtures of BaP₂O₆, Cu₃(PO₄)₂, CuO, V₂O₅ and V₂O₃ in evacuated closed quartz glas tubes. The compound crystallizes with tetragonal symmetry, Space group D? P42₁2, a = 9.560(2), c = 7.160(2) Å, Z = 2. Special and new features of the crystal structure are to each other isolated Cu₄O₁₂ and (VO)(PO₄)₄ groups. The crystal chemistry of the Cu₄O₁₂ groups is discussed with respect to other compounds containing out of plane connected square planar MO₄ polygones.     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .