Neue Oxocadmate der Alkalimetalle: K6[CdO4],Rb6[CdO4], Rb2CdO2 und Rb2Cd2O3

The crystal structure of K₆[CdO₄] and Rb₂CdO₂ has been determined from single crystal X-ray diffraction data and refined toR=0.058 (K₆[CdO₄]) andR=0.088 (Rb₂CdO₂). K₆[CdO₄] crystallizes hexagonal, space group P6₃mc with lattice constantsa=867.42 (6),c=665.5 (1) pm,c/a=0.767 andZ=2. It is isotypic with Na₆[ZnO₄]. Rb₂CdO₂ is orthorhombic, space group Pbcn witha=1045.0 (2),b=629.1 (1),c=618.3 (1) pm,Z=4, and crystallizes with the K₂CdO₂ structure type. The crystal structures can be deduced from the motif of a closest packed arrangement of O^2– with hexagonal (K₆[CdO₄]) or cubic (Rb₂CdO₂) stacking. The tetrahedra occupied by Cd²⁺ are isolated (K₆[CdO₄]) or edge-shared (formation of infinite SiS₂-like chains [CdO_4/2]) (Rb₂CdO₂). The powder diffraction pattern of Rb₆[CdO₄] [a=906.6 (1),c=694.3 (1) pm] and Rb₂Cd₂O₃ [a=642.6 (2),b=679.0 (1),c=667.9 (2) pm, =115.2 (1)] confirm isotypie with K₆[CdO₄] and K₂Cd₂O₃ respectively.

Herrn Prof. Dr.Gutman zum 65. Geburtstag gewidmet.     

K2Zn3O4 und Rb2Zn3O4, zwei neue Oxozincate mit Gerüststruktur [1]

K₂Zn₃O₄ and Rb₂Zn₃O₄, Oxozincates with Framework Structure For the first time single crystals of K₂Zn₃O₄ were obtained by heating mixtures of the binary oxides (K: Zn = 2.2:3) in sealed Ag- or Pt-capsules at 800°C (5 w). Powder of this colourless and moisture-sensitive oxide was prepared analogously at 500°C. It crystallizes monoclinic, space group C2/c with a = 1482.7(2), b = 637.3(1), c = 571,9(1) pm, β = 102.79(1)°, Z = 4, d_x = 4.265 g/cm³, d_pyk = 4.00 g/cm³. The crystal structure was determined from four-circle diffractometer data (MoKα, 730 unique hkl) and refined to R = 5.9%, R_w = 6.4%. It shows a Zn₃O₄ framework which consists of SiS₂-like chains [ZnO_4/2] connected by puckered layers of [ZnO_3/3]. The crystal structure can be derived from a cubic closet packing of O^2? and K⁺. Effective Coordination Numbers and the Madelung Part of Lattice Energy (MAPLE) are calculated. Rb₂Zn₃O₄ was prepared from the binary oxides at 400°C (colourless hygroscopic powder). According to powder data it crystallizes isostructural to K₂Zn₃O₄ with a = 1523.5(4), b = 649.8(2), c = 574.0(2) pm, β = 101.43(3)°, Z = 4, d_x = 5.141 g/cm³, d_pyk = 5.20 g/cm³.     

A new micro-fluid chip calorimeter for biochemical applications

Based on a new thermopile heat power sensor, which was developed in MEMS technology, a miniaturized flow-through calorimeter was constructed. The heat power sensor consists of a silicon chip with a thin film BiSb/Sb thermopile and a PMMA reaction chamber. To ensure high signal resolution the heat power sensor is mounted inside a high-precision thermostat, which has a temperature stability of less than 100 μK. The heat power sensitivity of the calorimeter is 4-7 V W⁻¹ depending on the thermal conductivity of the liquid, the height of the chosen reaction chamber and the volume flow rate. A limit of detection of less than 50 nW can be obtained for volume flows lower than 5 μl min⁻¹. An important advantage is the low sample consumption of the calorimeter. For special applications the sample need for one measurement pulse does not exceed 20 μl.     

Synthese und chemie von 4R-silacyclohexa-2,5-dienen und 4R-silacyclohexa-2,4-dienen

The 1(Z),4(Z)-1,5-dilithium-3R-3-methoxypenta-1,4-dienes, available by cleavage of 1,1-di-n-butyl-4R-4-methoxy-1-stannacyclohexane-2,5-dienes with n-BuLi in ether, react with dichlorosilanes (R′R″ SiCl₂; R′, R″ = H, alkyl, aryl, alkoxy) to give 1R′,1R″,4R-4-methoxy-1-silacyclohexa-2,5-dienes.Claevage of the ether group with BBr₃, BCl₃ or PCl₃ gives 6-chloro(bromo)-1-silacyclohexa-2,4-dienes or 1,5-dichloro-1-silacyclohexane-2,4-dienes, respectively.Ether cleavage of 4R-4-methoxy-1-silacyclohexa-2,5-dienes with sodium results in the formation of 4R-1-silacyclohexadienyl anions, which can be hydrolyzed to give 1-silacyclohexa-2,4-dienes which reach further with trichloromethylsilane to give 6-trimethylsilyl-1-silacyclohexa-2,4-dienes.Phase transfer-catalyzed conversion of 1-chlorosilacyclohexadienes into the fluoro derivatives as well as further substitution reactions of 1-chlorosilacyclohexadienes are described.The ¹H NMR, ¹³C NMR, IR and mass spectra of the silacyclohexadienes are discussed.     

Ein Natrium‐Oxocobaltat(II)‐Sulfat: Na8[CoO3][SO4]2

A Sodium Oxocobaltate(II) Sulfate: Na₈[CoO₃][SO₄]₂ Na₈[CoO₃][SO₄]₂ has been obtained from a redox reaction between cobalt metal and CdO in the presence of Na₂SO₄ and Na₂O at 550 °C (15 d) as red single crystals. The structure has been determined from single crystal data (IPDS‐data, T = 170 K, Cmcm, Z = 4, a = 806.88(9) pm, b = 2232.1(3) pm, c = 705.97(9) pm, R_all = 0.047). Magnetic properties and spectroscopic investigations are reported and discussed within the Angular‐Overlap‐Model.     

Darstellung und Strukturen von Mg‐Komplexen mit α, ω‐Dicarboxylato‐Liganden (Dicarboxylat = Succinat,Glutarat und Suberat)

Syntheses and Structures of Magnesium Complexes with α, ω‐Dicarboxylato Ligands; Dicarboxylate = Succinate, Glutarate, and Suberate Crystals of (Tetraaqua)(succinato)magnesium ( 1 ), (Tetraaqua)(glutarato)magnesium ( 2 ) und (Triaqua)(suberato)magnesium ( 3 ) were obtained by layering an aqueous solution of the respective sodium salt with a solution of MgCl₂ in isopropanol. In 1 a chain structure is realized. Mg(H₂O)₄ units are bridged in trans orientation by α, ω‐bonded succinate groups. 2 contains also chains. Glutarato groups are bonded in a cis fashion to Mg(H₂O)₄ units. They form bridges by using their two α O atoms. 3 represents a layer structure. The basic structural motives are α, α, ω‐bonded suberate, and fac‐Mg(H₂O)₃ units. All three structures contain efficient H bridging systems. The connection between the symmetry of the polymeric groups (chains or layer) and the symmetry of the underlying space groups is discussed. 1 : Space group P2₁/c, Z = 4, lattice constants at 20 °C: a = 7.441(2), b = 14.827(2), c = 7.771(2) Å; β = 99.77(3)°, R1 = 0.052. 2 : Space group C2/c, Z = 8, lattice constants at 20 °C: a = 12.867(2), b = 7.109(1), c = 21.683(3) Å; β = 107.33(2)°; R₁ = 0.032. 3 : Space group P2₁/a, Z = 4, lattice constants at 20 °C: a = 9.174(2), b = 8.071(2), c = 15.960(3) Å; β = 104.29(2)°; R₁ = 0.052.     

Dicarboxylatgruppen als Liganden und Anionen in Aquamagnesiumkomplexen: Kristallstrukturen von [Mg (C4H2O4)(H2O)4] · H2O und [Mg(H2O)6](C4HO4)2 · 2H2O ((C4H2O4)2— = Fumarat; (C4HO4)— = Hydrogenacetylendicarboxylat)

Dicarboxylate Groups as Ligands and Anions in Aquamagnesium Complexes: Crystal Structures of [Mg (C₄H₂O₄)(H₂O)₄] · H₂O and [Mg(H₂O)₆](C₄HO₄)₂ · 2H₂O ((C₄H₂O₄)^2— = Fumarate; (C₄HO₄)^— = Hydrogenacetylenedicarboxylate) Crystals of tetraaqua(fumarato)magnesium‐hydrate ( 1 ) and hexaaquamagnesium‐bis(hydrogenacetylenedicarboxylate)‐dihydrate ( 2 ) were prepared by reacting MgCl₂ with sodium fumarate and acetylenedicarboxylic acid, respectively. In 1 cis‐Mg(H₂O)₄ units are bridged by α, Ö‐bonded fumarate groups. The resulting zig zag chains exhibit the maximum symmetry compatible with space group symmetry C2/c. 2 consists of layers of voluminous [Mg(H₂O)₆]²⁺ cations alternating with layers of C₄HO₄^— anions. The nearly planar anions are held together by parallel stacking and by short hydrogen bonds. Both structures contain efficient H bridging systems. 1 : Space group C2/c, Z = 4, lattice constants at 20 °C: a = 5.298(1), b = 13.178(2), c = 13.374(2)Å; ß = 94.79(2)°, R₁ = 0.024. 2 : Space group P1, Z = 1, lattice constants at 20 °C: a = 5.985(1), b = 6.515(1), c = 11.129(1)Å; α = 105.24(2), ß = 91.87(3), γ = 90.92(1)°, R₁ = 0.034.     

Characterizing correlation changes of complex pattern transitions: The case of epileptic activity

We analyze the time-dependent spectrum of eigenvalues of the correlation matrix for multivariate EEG data at the transition to epileptic seizures. By a mechanism of level repulsion between states at both edges of the spectrum of the correlation matrix, relevant information about quantitative correlation changes is reflected in the largest and smallest eigenvalues and corresponding eigenvectors. By the application of measures from random matrix theory we provide evidence that statistically relevant information can be obtained both at the upper and the lower end of the spectrum. In addition, information about spatial characteristics of correlation changes can be extracted.     

Single and double ionization of the hydrogen molecule in an intense few-cycle laser pulse

In this paper, we present ab initio two-electron model calculations of laser-induced single and double ionization of the hydrogen molecule in a linearly polarized laser field with static nuclei located along the polarization axis. Within the model, the center-of-mass motion of the two electrons is restricted along the polarization axis of the field, while the relative electron motion is unrestricted. The results of numerical simulations allow us to identify and characterize the mechanisms leading to single and double ionization in an intense few-cycle laser pulse. The role of the rescattering mechanism on the ionization processes is analyzed in particular.     

Study of an order-disorder phase transition on an atomic scale: the example of decagonal Al-Ni-Co quasicrystals

In the present paper we succeeded in studying structural phase transitions from an atomistic point of view by positron annihilation Doppler broadening. This differs and is complementary to conventionally used diffraction experiments with large coherence lengths. In the exemplary case of the 1140 K order-disorder transition in decagonal Al71.5Ni14Co14.5 quasicrystals the importance of this atomistic approach and its wide scope of application is demonstrated.