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.     

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.     

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.     

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.     

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.     

Smectic polymorphism of the 4-butyl-4-alkoxyazobenzenes and 4-pentyl-4-alkoxyazobenzenes

Two families of liquid crystalline compounds have been synthesised, the 4-butyl-4- alkoxyazobenzenes and the 4-pentyl-4-alkoxyazobenzenes; for the second family results are presented for the first time for alkoxy chains longer than butyl. The results for both families have been obtained up to the octadecyl homologues. In both families, on the basis of DSC, polarizing microscopy and thermo-optical analysis, a rich polymorphism has been detected (maximum tetramorphism). The smectic properties start with the hexyl derivative (for the butyl family) and with the heptyl derivative (for the pentyl family). Strong odd-even effects for the temperatures of clearing in both groups of compounds were detected. Our results are compared with those of de Jeu et al. and of Adomenas et al. for the 4-butyl-4- alkoxyazobenzenes, for which only one smectic modification was described.     

Synthesis of 4-alkoxy-4-methyl- and 4-alkoxy-4-fluoromethyl-1,3-benzoxazinones

Cyclization of 2-hydroxyacetophenone hydrazones with triphosgene resulted in the formation of 4-methylene-1,3-benzoxazinones. These compounds were converted to 4-alkoxy-4-methyl-1,3-benzoxazinones and 4-fluoromethyl-4-methoxy-1,3-benzoxazinones upon treatment with alcohols under refluxing conditions and F-TEDA-BF₄ in acetonitrile and methanol, respectively.     

Stabilization Studies on Divalent Five‐Membered Rings C4H4C,C4H4Si,C4H4Ge,C4H4Sn,and C4H4Pb

Energy differences, ΔX_S‐t (X = E, H and G) (ΔX_S‐t = X_(singlet)‐X_(triplet)) between singlet (s) and triplet (t) states are calculated at B3LYP/6‐311++G (3df,2p). The DFT calculations show that the triplet state of C₄H₄C is a ground state with planar conformer respect to its corresponding nonplanar singlet state. Both singlet and triplet states of C₄H₄M (M = Si, Ge, Sn and Pb) have a planar conformer with the singlet ground state. Four isodesmic reactions are presented for determining the stability energies, SE. NICS calculations are carried out for C₄H₄M to determine the aromatic character.     

4-巯基-4-脱氧-4'-去甲表鬼臼毒素的立体控制合成

4-巯基-4-脱氧-4'-去甲表鬼臼毒素是合成4位硫取代的4'-去甲表鬼臼毒素的关键中间体,由4'-去甲表鬼臼毒素与硫化氢在BF~3·Et~2O存在下立体控制制备,也可通过以NH~3/CH~CN选择性 地水解4-乙酰硫基-4-脱氧-4'-去甲表鬼臼毒素而制备.     

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.     

4-Hydroxy-4′-ethynylazobenzene

Summary 4-Hydroxy-4-ethynylazobenzene was obtained by the chlorination and dehydrochlorination of 4-hydroxy-4-acetylazobenzene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1674–1675, September, 1965     

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.