bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental toxicity evaluation of ibuprofen and tolmetin administered in triple daily doses to Wistar CRL:(WI)WUBR rats
Authors: Burdan Franciszek
Published: October 2004

BACKGROUND: Ibuprofen and tolmetin are popular non‐steroidal anti‐inflammatory drugs. Previous animal studies taken with single daily doses showed their good prenatal tolerability. However, since both cyclooxygenase (COX) inhibitors have a short half‐life, the current report presents drug developmental effects after triple daily doses administration, as they are used in human. METHODS: Drugs were separately, orally dosed to pregnant rats triple daily 8 hr apart from day 8 to 21 (GD=1‐plug day). The total daily doses were set at 25.5, 255.0, and 600.0 mg/kg for ibuprofen and 25.5, 255.0, and 2550.0 mg/kg for tolmetin. Fetuses were delivered on GD 21 and routinely examined. Comprehensive clinical and developmental measurements were done. RESULTS: Maternal toxicity and intrauterine growth retardation were found in groups exposed to the highest doses of both drugs. An increase of external variations was reported in groups exposed to the middle and highest dose of ibuprofen and to the highest dose of tolmetin. Skeletal variations were significantly different only in litters treated with the highest doses of the drugs. Pooled statistical analysis showed a higher incidence of midline and ventricular septal (VSD) defect in rat fetuses exposed to COX inhibitors when compared with historical control data. For ibuprofen, the influence on VSD was similar to aspirin. CONCLUSION: Both COX inhibitors were toxic to dams in the highest doses evaluated, which caused a significantly greater incidence of intrauterine growth retardation and developmental variations. Birth Defects Res B 71:321–330, 2004. © 2004 Wiley‐Liss, Inc.
Detection of tissue‐specific effects by methotrexate on differentiating mouse embryonic stem cells
Authors: Pellizzer Cristian , Bello Ezia , Adler Sarah , Hartung Thomas , Bremer Susanne
Published: October 2004

BACKGROUND: Pluripotent embryonic stem (ES) cells offer a unique possibility to monitor the differentiation of several cell types in vitro. This study attempts to identify marker genes during in vitro cell differentiation of murine ES cells and allow a prediction of chemical effects on cell differentiation of specific target tissues. The study focused on the expression pattern of key genes involved in cardiomyocyte and osteoblast differentiation: Oct‐4, Brachyury, Nkx2.5, α myosin heavy chain, Cbfa1, and Osteocalcin. METHODS: Methotrexate was selected due to its well‐characterized teratogenic effects. Several in vivo studies have demonstrated the specific interactions of methotrexate with bone formation whereas the cardiovascular system is not specifically affected after exposure to low concentration. The capability of murine ES cells to differentiate in vitro into cardiomyocytes as well as into osteoblasts have been used to demonstrate the target cell specificity in vitro, at non‐cytotoxic concentration. RESULTS: Exposure of differentiating ES cells did not result in any gene profile modification of the selected cardiomyocyte specific genes, whereas the expression of osteoblast specific key genes, Cbfa1 and Osteocalcin, decreased. At the latter stages of skeletal differentiation we observed a 30% decrease in gene expression for Cbfa1 and a 60% decrease for Osteocalcin, with reference to the control. Early marker genes for undifferentiated cells and mesodermal cells were not modified after methotrexate treatment. CONCLUSIONS: These results show the possibility to integrate specific in vitro tests for teratogenicity in a test strategy for developmental toxicity. Birth Defects Res B 71:331–341, 2004. © 2004 Wiley‐Liss, Inc.
Die Rolle des Animismus bei der Vermittlung chemischer Sachverhalte
Authors: Püttschneider Martin , Lück Gisela
Published: October 2004

Wie lassen sich Naturphänomene und deren naturwissenschaftliche Deutung motivierend und nachhaltig vermitteln? Eine wirklich befriedigende Antwort scheint wohl nicht gefunden zu sein, denn Chemie gilt in der öffentlichen Diskussion immer noch als unverständlich. Nicht ohne Grund wurde Ende der 80er Jahre das PUSH‐Programm entwickelt (Public Understanding of Science and Humanities). In diesem Programm sollen einer breiten Öffentlichkeit wissenschaftliche Begriffe, Problemstellungen und Konzepte verständlich dargeboten werden, so dass es zu einer Wertschätzung der naturwissenschaftlichen und technischen Beiträge in der Gesellschaft kommt [1].

Verständliche Vermittlung muss frühzeitig in der Schule beginnen, da dort die Grundlagen für ein nachhaltiges Interesse an naturwissenschaftlichen Fragestellungen gelegt werden. Ein nachlassendes Interesse gegenüber naturwissenschaftlichen Fächern, insbesondere Chemie und Physik, zeigt sich bereits im Verlauf der Sekundarstufe I. Höner und Greiwe bestätigen Untersuchungen der Vorjahre und stellen fest: „In der 7. Klasse ist Chemie noch das drittbeliebteste Fach … Im Verlauf der Jahrgangsstufen verschlechtert sich der Wert in der neunten sowie noch einmal in der zehnten Klasse … zu den unbeliebtesten Fächern.”︁ [2] Es ist anzunehmen, dass die nachlassende Fachbeliebtheit auch langfristig und nachhaltig zu einem rückläufigen Interesse an chemischen Sachverhalten führt.

Neben verschiedenen ursächlichen Faktoren ist hier insbesondere die Art der Vermittlung zu nennen. Der bewusste Einsatz von Animismen könnte durch seinen motivierenden Charakter einem nachlassenden Interesse entgegenwirken.
In vitro and in vivo characterization of TC‐1827, a novel brain α4β2 nicotinic receptor agonist with pro‐cognitive activity
Authors: Bohme Georg Andrees , Letchworth Sharon R. , Piot‐Grosjean Odile , Gatto Gregory J. , Obinu Marie‐Carmen , Caldwell William S. , Laville Michel , Brunel Pascale , Pellerin Rachel , Leconte Jean‐Pierre , Genevois‐Borella Arielle , Dubedat Pierre , Mazadier Martine , Pradier Laurent , Bencherif Merouane , Benavides Jesus
Published: October 2004

Nicotine activates specific receptors that are cation‐permeable ionic channels located in the central and autonomous nervous systems, as well as at the neuromuscular junction. Administration of nicotine to animals and humans has been shown to enhance cognitive processes. However, side effects linked to the activation of peripheral nicotinic receptors limit the usefulness of nicotine for the treatment of cognitive disorders such as Alzheimer's disease (AD) or mild cognitive impairments (MCI). The synthesis and properties of TC‐1827, a novel metanicotine derivative that activates brain α4β2 nicotinic receptors is described. TC‐1827 has high affinity for nicotine‐labeled receptors in the cortex (Ki=34 nM), full‐agonist intrinsic activity in α4β2‐mediated neurotransmitter release studies in synaptosomes, and has no functional activity at nicotinic receptors in ganglionic or muscular cell lines. The compound enhances long‐term potentiation in hippocampal slices, a form of synaptic plasticity thought to be involved in information storage at the cellular level. In vivo studies demonstrate that TC‐1827 dose‐dependently occupies thalamic nicotinic receptors labeled with [3H]‐cytisine, increases cortical extracellular acetylcholine levels following oral administration, and enhances cognitive performance in rat and mice behavioral procedures of learning and memory. Pharmacokinetic studies in mice, rats, and monkeys indicated that TC‐1827 has good oral absorption with a first pass effect resulting in bioavailabilities of 13–65% across dose/species. Cardiovascular safety studies indicate good cardiovascular tolerability for this compound. The present data demonstrate that TC‐1827 is a selective and potent activator of brain α4β2 nicotinic receptors and is a prototypical member of a new class of compounds with potential utility in the symptomatic treatment of cognitive disorders including AD and MCI. Drug Dev. Res. 62:26–40, 2004. © 2004 Wiley‐Liss, Inc.
KP544, a nerve growth factor amplifier: Pharmacokinetics, safety, and efficacy in the rat
Authors: Krenitsky Thomas A. , Dillberger John , Zotova Elena , Arezzo Joseph C. , Koprich James B. , Mortazavi Farzad , Gates Timothy A. , Dunbar Gary L.
Published: October 2004

In cultured cells, KP544 [2‐amino‐5‐(4‐chlorophenylethynyl)‐4‐(4‐trans‐hydroxycyclohexyl amino) pyrimidine] amplifies differentiation initiated by nerve growth factor (NGF) or cAMP. This report describes the pharmacokinetics, safety, and neuroprotective efficacy of KP544 in rats. After an oral dose of 10 mg/kg KP544 was 25% bioavailable with a plasma half‐life of 1.3 h and brain levels 6‐fold higher than plasma levels at 4 and 8 h post‐dose. In a safety study, daily oral dosing for 30 days at 10 and 100 mg/kg was well tolerated. The favorable pharmacokinetic and safety profiles, together with its amplification of NGF in vitro, prompted evaluation of KP544 in two models involving NGF deficiencies. In the first model, brains were lesioned with intrastriatal injections of quinolinic acid. KP544 at oral doses of 0.02 to 1.0 mg/kg/day almost completely prevented the resulting learning deficits as evaluated using a radial‐arm‐water maze. At the lowest dose, there was a slower onset of functional improvement. These effects were accompanied by reductions (16–34%) in the striatal lesion size that were greatest at the highest dose and comparable to those seen with NGF therapy. The second model involved a peripheral neuropathy induced by taxol that is associated with decreases in NGF. KP544 at oral doses of 0.1–10 mg/kg/day decreased the severity of the neuropathy as measured by caudal nerve conduction velocities (30–70% return to control values). In both models, KP544 had a large therapeutic index suggesting its potential as a new approach for treating clinical disorders involving deficiencies in NGF. Drug Dev. Res. 62:60–70, 2004. © 2004 Wiley‐Liss, Inc.
Thallium−Arene Contacts in a Rare Yttrium Tris(pyrazolyl)hydroborate “ate” Complex
Authors: Kunrath Fábio A. , Casagrande Osvaldo L. , Toupet Loic , Carpentier Jean‐François
Published: October 2004

A salt elimination reaction between [YCl3(THF)3.5] and 1 or 2 equiv. of Tl(TpMs*) [TpMs* = HB(3‐mesitylpyrazolyl)2(5‐mesitylpyrazolyl)−] leads in both cases to single metathesis, giving a mixture of the mono‐TpMs* complex [YCl3(TpMs*)Tl] (1) and another complex, [YCl2(TpMs**)] (2) [TpMs** = HB(3‐mesitylpyrazolyl)(5‐mesitylpyrazolyl)2−], that results from the transfer of a second mesityl group to the 5‐position of the pyrazolyl ring. The solid‐state structure of 1 shows a unique “ate” dimeric structure with the Tl+ cations coordinated by two μ2‐ and two μ3‐bridging Cl atoms as well as two η3‐mesityl ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Diastereomeric Halfsandwich Rhenium Complexes Containing Hemilabile Phosphane Ligands
Authors: Dilsky Stefan , Schenk Wolfdieter A.
Published: October 2004

The syntheses and some typical reactions of diastereomeric rhenium complexes [CpRe(NO)(CO){P(Ph)(R)(R′)}]BF4 (R = Me, Ph; R′ = 2‐C6H4OMe, CH2C4H3S, CH2C4H7O) (3a−e) are described. Reduction of the carbonyl ligand with NaBH4 in THF gave the corresponding methyl complexes [CpRe(NO){P(Ph)(R)(R′)}(CH3)] (4a−e). Acid treatment of the methyl complexes leads to liberation of methane and coordination of the additional donor site of the potentially bidentate phosphane ligand. Of the chelate complexes 5a−e, those with R′ = 2‐C6H4OMe (5a, d) decomposed in solution at room temperature. In donor solvents, the chelate ring opens giving the stable solvated complexes [CpRe(NO){P(Ph)(R)(R′)}](solvent)]BF4 (solvent = CH3CN, THF) (6b−e, 7d). The new compounds are thus suitable starting materials for the syntheses of diastereomeric rhenium complexes [CpRe(NO){P(Ph)(R)(R′)}(L)]BF4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Macromol. Theory Simul. 8/2004
Authors: Pirozzi Beniamino , Napolitano Roberto , Esposito Simona
Published: October 2004

Cover: The figure shows the map of the conformational energy of syndiotactic 1,2‐poly(1,3‐butadiene) in the crystalline field as a function of the two independent torsion angles in the main chain. The loci of the points corresponding to the helical s(2/1)2 symmetry of the chain and the point corresponding to the tcm symmetry are also shown. Energy maps have been calculated also for various vinyl polymers deriving from 1,3‐diene monomers in order to predict the values of the conformational parameters for each polymer.

Further details can be found in the Full Paper by B. Pirozzi,* R. Napolitano, and S. Esposito on page 679.
Structural and spectral assignment by two‐dimensional NMR of two new derivatives of the abietane diterpenoid taxodione
Authors: Rodríguez Benjamín
Published: October 2004

Two new abietane derivatives were obtained by treatment of the diterpene taxodione with diazomethane. Their structures were determined by mass spectrometry and NMR studies, including one‐ and two‐dimensional experiments. Copyright © 2004 John Wiley & Sons, Ltd.
Investigation of the association and flexibility of cationic lipidic peptide dendrons by NMR spectroscopy
Authors: Zloh Mire , Ramaswamy Chandrasekaran , Sakthivel Thiagarajan , Wilderspin Andy , Florence Alexander T.
Published: October 2004

The cationic peptide dendrons synthesized and studied are lower generation polylysine‐based partial dendrimers with or without lipid chains in the core. The dendrons with lipidic chains can be utilized as protein and liposomal mimics because of their unique structural properties. The full assignments of three different dendrons (L)7(NH2)8, (C14)1(L)7(NH2)8 and (C14)3(L)7(NH2)8 were obtained in D2O and H2O/D2O using a 500 MHz NMR spectrometer. The hydrophobic lipidic core of branched polylysine dendrons was found to induce aggregation upon increasing concentration. Because non‐lipidic dendrons do not self‐assemble, the behaviour and internal structural features of two different dendrons with one and three C14 hydrocarbon chains were explored. The critical association concentration clearly depends on the number of core hydrophobic residues and the association starts at 0.025 mM for (C14)1(L)7(NH2)8 and 0.05 mM for (C14)3(L)7(NH2)8. Chemical shift analysis also revealed that the hydrophobic chains of the dendrons associate in the core, whereas the polar head groups (NH2) are mainly located at the surfaces of the aggregates. The T1 relaxation time measurements showed that the mobility of the hydrocarbon chain is greater with the monomeric form of dendron (C14)1(L)7(NH2)8 than that of monomer (C14)3(L)7(NH2)8. The inter‐chain hydrophobic interactions restrict the flexibility of the dendron with three hydrocarbon chains. As expected, the flexibility of the monomeric form is higher than that of the aggregated state for both of the dendrons. Copyright © 2004 John Wiley & Sons, Ltd.
Effects of the volume and temperature on the global and segmental dynamics in poly(propylene glycol) and 1,4‐polyisoprene
Authors: Roland C. M. , Paluch M. , Casalini R.
Published: October 2004

Published dielectric relaxation measurements for poly(propylene glycol) and 1,4‐polyisoprene are analyzed to determine the relative effects that thermal energy and volume have on the temperature dependence of the normal‐mode relaxation times, and these are compared with their effects on the temperature dependence of the local segmental relaxation times. For both polymers at temperatures well above the glass‐transition temperature, both relaxation modes are governed more by the thermal energy than by the volume, although the latter's contribution is not negligible. Such a result is consistent with an assumption underlying models for polymer viscoelasticity, such as the Rouse and tube models, that the friction coefficient governing motions over large length scales can be identified with the local segmental friction coefficient. Moreover, the relaxation data for both the segmental and normal modes superimpose when expressed as a function of the product of the temperature and volume, the latter being raised to a power. This scaling form arises from an inverse power law for the repulsive part of the intermolecular potential. The value of the exponent on the volume is the same for the normal and segmental motions and for both polymers indicates a relatively soft potential. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4313–4319, 2004
Raman scattering studies in two kinds of Ge nanosystems under hydrostatic pressure
Authors: Teo K. L. , Shen Z. X. , Liu L. , Kolobov A. V. , Maeda Y.
Published: October 2004

We report Raman scattering of Ge nanocrystals (NCs) embedded in SiO2 matrix on Si substrate (Ge/SiO2/Si) and on quartz substrate (Ge/SiO2/quartz) under hydrostatic pressure. The pressure coefficient obtained for the Ge mode in the Ge/SiO2/quartz nanosystem is found to be almost twice as large com‐ pared with its corresponding bulk value. We explained our results using a simple elastic model, which describes the effective pressure transmitted from the matrix to the NCs. In Ge/SiO2/Si nanosystem, delamination of the SiO2 film from the Si substrate occurs at ∼23 kbar due to the large difference between the compressibility of the SiO2 matrix and Si substrate. The observed effect can be understood by the nonhomogeneous distribution of the elastic field in the Ge/SiO2/Si nanosystem using a finite element analysis. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure‐induced phase transition in ErH3
Authors: Moysés Araújo C. , Ferreira da Silva Antonio , Ahuja R.
Published: October 2004

The pressure‐induced structural phase transition in ErH3 is investigated using ab initio calculations. The electronic structure is calculated using the projected augmented wave (PAW) method and the transition pressure is obtained by fitting the energy–volume set to the Murnaghan equation of states. A structural phase transformation has been found accompanied by an insulator–metal transition at 17.0 GPa in good agreement with experimental findings. A similar phase transition is also predicted for GdH3. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of hydrostatic pressure on optical properties of InN and In‐rich group III‐nitride alloys
Authors: Li S. X. , Wu J. , Walukiewicz W. , Shan W. , Haller E. E. , Lu Hai , Schaff William J. , Saito Yoshiki , Nanishi Yasushi
Published: October 2004

We have used the diamond anvil cell technique to measure the hydrostatic pressure dependence of the optical absorption edge and photoluminescence peak energy of MBE grown InN, In‐rich In1–xGaxN (0 < x < 0.5) and In1–xAlxN (x = 0.25) alloys. Together with previous reports, our results show that the pressure coefficient of the absorption edge varies monotonically from about 3.0 ± 0.1 meV/kbar for InN to 4.2 meV/kbar in GaN and to 4.9 meV/kbar in AlN. The photoluminescence measurements yield significantly smaller pressure coefficients than the coefficients of the bandgap, which is attributed to emission associated with recombination via highly localized defect states. Samples which give small photoluminescence pressure coefficient usually have large Stokes shift. Based on the results of the absorption and photoluminescence measurements we are able to determine the absolute deformation potentials of the conduction and valence band edges of these alloys. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence of CaS:Eu2+ under hydrostatic pressure
Authors: Chen C. , Teo K. L. , Chong T. C. , Newman D. M.
Published: October 2004

We have studied the hydrostatic pressure dependence of the emission of CaS doped with Eu2+. For P ≥ 70 kbar, we observed the main the emission peak broadens and appears to ‘split’ into two peaks with the low‐energy peak increasing in intensity relative to the main energy peak. We proposed that more than one excited state could be thermally populated at room temperature. The quenching of the luminescence can be explained by the presence of an intervening state using a single configuration coordinate model. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman scattering studies of Ge/Si islands under hydrostatic pressure
Authors: Teo K. L. , Shen Z. X. , Schmidt O. G.
Published: October 2004

Raman scattering under hydrostatic pressure is used to investigate the phonon modes of self‐assembled Ge islands grown by solid source molecular beam epitaxy. Our results show that the overlapping spectra of the Ge–Ge phonon and Si 2TA modes occur around 304 cm–1 at ambient pressure can be resolved at relatively low pressure of about 3 kbar. The mode Grüneisen parameter of the Ge–Ge phonon mode in quantum dot is found to be γ = 0.84 ± 0.01. The normalized Raman intensity profiles of Ge–Ge mode, exhibits a resonance enhancement peak at 2.37 eV. The pressure coefficient of this resonating electronic transition is ∼2.7 ± 0.5 meV/kbar, which is significantly smaller than the pressure shift of the E1 transition in bulk Ge. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature and pressure dependence of recombination processes in 1.5 μm InGaAlAs/InP‐based quantum well lasers
Authors: Sweeney S. J. , McConville D. , Massé N. F. , Bouyssou R.‐X. , Adams A. R. , Ahmad C. N. , Hanke C.
Published: October 2004

The improved thermal stability of InGaAlAs‐based lasers compared with InGaAs‐based lasers for 1.5 μm operation is investigated using a combination of low temperature and high pressure techniques. The results indicate that the improved performance of InGaAlAs‐based devices is due to a reduction in the contribution of the non‐radiative Auger recombination current, IAug, to the total threshold current, Ith, in the InGaAlAs devices. This is due to the higher conduction band offset made possible with the InGaAlAs system which results in a lower hole density in the quantum wells at threshold. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theory of electron confinement and electron effective mass in dilute nitride alloys and heterostructures
Authors: O'Reilly E. P. , Lindsay A. , Tomić S. , Klar P. J.
Published: October 2004

The band‐anti‐crossing (BAC) model describes the strong band‐gap bowing at low N composition x in Ga(In)NxAs1–x in terms of an interaction between the conduction band edge and a higher‐lying band of localized nitrogen resonant states. We first present an analytical technique based on the BAC model to calculate electron energies in Ga(In)NAs square quantum well (QW) structures. We then show through detailed comparison with photoreflectance measurements that the BAC model successfully describes ground and excited state interband transition energies in bulk and QW GaNAs samples, both at ambient pressure and as a function of hydrostatic pressure. Turning to the conduction band dispersion, we find that the two‐level BAC model is insufficient, and must be modified to give a quantitative understanding of the unexpectedly large electron effective mass values observed in some GaNAs samples, which we attribute to hybridisation between the conduction band edge and nitrogen states close to the band edge. We predict a non‐monotonic variation of electron mass with hydrostatic pressure in many GaNAs samples. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aortopulmonary window with ventricular septal defect and pulmonary atresia: prenatal diagnosis and successful early surgical correction
Authors: Kuehn A. , Oberhoffer R. , Vogt M. , Lange R. , Hess J.
Published: October 2004

We report a case in which aortopulmonary window (APW) in combination with pulmonary atresia was diagnosed correctly in a neonate by echocardiography. Prenatal echocardiography showed progression of tetralogy of Fallot to pulmonary atresia with retrograde pulmonary perfusion, concealing the concomitant APW in fetal life. Due to intractable heart failure, primary correction was successfully performed at the age of 4 weeks (weight 2280 g). Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Sr10[Mo2N6][MoN4]2 and β‐Sr3MoN4
Authors: Bailey Mark S. , McGuire Michael A. , DiSalvo Francis J.
Published: October 2004

Two new phases in the strontium‐molybdenum‐nitrogen phase diagram have been synthesized. Single crystals of Sr10[Mo2N6][MoN4]2 were grown from a mixed sodium‐gallium melt at 900 °C in a sealed niobium tube. It crystallizes in the triclinic space group $P{\bar 1}$ (Z = 1) with a = 6.421(1), b = 9.190(2), c = 9.263(2) Å and α = 64.939(5), β = 82.961(6) and γ = 89.692(6)°. The new, orthorhombic polymorph of Sr3MoN4 was synthesized as a polycrystalline powder from an intimate mixture of Sr2N and molybdenum metal in the presence of N2. Rietveld analysis shows it to crystallize in Pbca (Z = 8) with a = 10.4835(2), b = 9.7374(2) and c = 11.5114(2) Å. Studies suggest that excess nitrogen is essential to the formation of this polymorph. Sr10[Mo2N6][MoN4]2 is the first molybdenum nitride to contain the anionic unit [Mo2N6]8‐, which appears as isolated, edge‐sharing pairs of MoN4 that facilitate MoV‐MoV bonding. This compound also contains isolated [MoN4]6‐ tetrahedra and the presence of these two units results in the first mixed valent molybdenum nitride. Resistivity measurements show it to be insulating.
Einkristalluntersuchungen an Cs[AuF4], Cs[Au2F7] und U2F7[AuF4]
Authors: Schmidt R. , Müller B. G.
Published: October 2004

Anhand von Einkristalldaten konnte mit blaßgelbem Cs[AuF4] das letzte Alkalimetallfluoroaurat M[AuF4] (M = Li‐Cs) strukturell charakterisiert werden. Es kristallisiert orthorhombisch in einem neuen Strukturtyp, Immm (Nr.71) mit a = 548, 6, b = 658, 9 und c = 1265, 5 pm, Z = 4.

Als Nebenprodukt wurde gelb‐braunes Cs[Au2F7] erhalten. Die Verbindung kristallisiert monoklin, C2/c (Nr.15) mit a = 1136, 5, b = 1082, 0 und c = 737, 4 pm, β = 123, 4, Z = 4. Charakteristisches Strukturmerkmal ist die bei Fluoroauraten bislang erstmals beobachtete [Au2F7]‐‐Baugruppe.

Schließlich gelang noch die gezielte Synthese von blaßgelbem U2F7[AuF4]. Die Atomanordnung entspricht der in Th2F7[AuF4] (I4/mmm, a = 1132, 37, c = 632, 99 pm, Z = 4).
Kopplung metallorganischer Reaktionszentren durch den nichtplanaren Brückenliganden 2, 3‐Bis(2‐pyridyl)pyrazin
Authors: Berger Sascha , Scheiring Thomas , Fiedler Jan , Kaim Wolfgang
Published: October 2004

Der vielverwendete Ligand 2, 3‐bppz = 2, 3‐Bis(2‐pyridyl)pyrazin und seine Komplexe [(2, 3‐bppz){(C5Me5)ClM}n](PF6)n, M = Rh oder Ir und n = 1 oder 2, wurden durch cyclische Voltammetrie und UV/VIS‐Spektroelektrochemie untersucht. Sowohl für die einkernigen als auch — ungewöhnlicherweise — für die zweikernigen Komplexe werden nur Chlorid‐dissoziative Zweielektronenreduktionsprozesse beobachtet. Einer der Vorläuferkomplexe, [(2, 3‐bppz)(C5Me5)ClIr]Cl·2H2O, konnte strukturell charakterisiert werden, er weist eine deutlich nichtplanare Konformation des 2, 3‐bppz‐Liganden auf.
K10M4M′4S17 (M = Mn, Fe, Co, Zn; M′ = Sn, Ge) and Cs10Cd4Sn4S17: Compounds with a Discrete Supertetrahedral Cluster
Authors: Palchik Oleg , Iyer Ratnasabapathy G. , Canlas Christian G. , Weliky David P. , Kanatzidis Mercouri G.
Published: October 2004

The cluster compounds K10Zn4Sn4S17, K10Mn4Sn4S17, K10Fe4Sn4S17, K10Co4Sn4S17, Cs10Cd4Sn4S17 and K10Zn4Ge4S17 are described. The structures of these compounds, refined by single‐crystal X‐ray diffraction techniques, contain the discrete cluster [M4M′4S17]10‐ (M = Zn, Mn, Co, Fe, Cd; M′ = Sn or Ge) which has the structure of Si8C17H36. It is built from the sulfur‐connected tetrahedral SnS4 and MS4 units with the additional quadruply bridging sulfur atom at the center of the cluster. All compound show some solubility and stability in water and formamide. Cs10Cd4Sn4S17 and K10Zn4Ge4S17 show photoluminescence at room temperature.The magnetic properties of K10Mn4Sn4S17, K10Fe4Sn4S17, K10Co4Sn4S17 indicate strong antiferromagnetic interactions arising from spin coupling within the cluster but their magnetic susceptibility is characterized with a discrepancy between field‐cooled and zero field‐cooled measurements.
Anion Distribution in Zr2ON2
Authors: Bredow Thomas , Lerch Martin
Published: October 2004

The effect of the distribution of N and O ions on the lattice energy of Zr2ON2 has been investigated with periodic first‐principles calculations. It was found that the ordered Ibca structure is energetically unstable with respect to interchanges of N and O atoms. The stabilization has been correlated with the N‐N and O‐O coordination. The average coordination numbers of the most stable configuration are similar to those of a statistical anion distribution. The calculated electronic structure is in agreement with experimental observations.
Two Novel Thioantimonates(III) with the Same Stoichiometric Sb:S Ratio but Different Crystal Structures: Solvothermal Synthesis, Crystal Structures, Thermal Stability and Spectroscopy of (C6N3H17)Sb6S10 and (C7N2H13)3Sb9S15
Authors: Spetzler Volker , Kiebach Ragnar , Näther Christian , Bensch Wolfgang
Published: October 2004

The two novel thioantimonates(III) (C6N3H172+)Sb6S10 (I) and (C7N2H13+)3Sb9S15 (II) were synthesized under solvothermal conditions reacting Sb and S with the amines 1‐(2‐aminoethyl)‐piperazine (C6N3H15) and 1, 5‐diazabicyclo[4.3.0.]non‐5‐en (DBN, C7N2H12), respectively. The compounds crystallize as red needles in the monoclinic non‐centrosymmetric space group P21 (I) and in the monoclinic space group P21/c (II) with lattice parameters a = 6.120(4) Å, b = 17.759(1) Å, c = 11.478(7) Å, β = 90.70(7)° for I and a = 10.2643(6) Å, b = 23.648(2) Å, c = 20.4655(11) Å, β = 104.430(7)° for II.

In both compounds the primary building units (PBUs) are trigonal SbS3 pyramids and SbS4 moieties. The interconnection of these PBUs leads to the formation of six‐membered rings Sb3S3 and Sb3S4 semi‐cubes in I which are joined via common S atoms to form the one‐dimensional [Sb6S10]2‐ anion being directed along [001]. Neighbored chains are arranged in a way that pockets are formed which host the organic cations. The ammonium groups of the organic molecules are oriented towards the anion ensuring optimal S···H bonding interactions. Taking into account the longer Sb‐S bonds above 3Å a three‐dimensional network is formed with large cages containing the organic cations. In compound II the SbS3 pyramids and the SbS4 units each form individual chains by vertex linking. The central chain is exclusively formed by SbS4 units whereas the other two chains are composed of SbS3 pyramids. The interconnection of the chains via common corners yields the one‐dimensional [Sb9S15]3‐ multiple chain anion. Due to the connection mode Sb4S4 rings are formed which are condensed along [001]. The chains are stacked along [100] with an inter‐chain separation of about 7Å. In the [010] direction the anions are lined‐up with the shortest distance between neighbored anions of about 3.4Å. With the long Sb‐S distances layers within the (100) plane are formed. At elevated temperatures both compounds decompose via an internal redox reaction into Sb2S3 (Stibnite) and Sb. The optical band gaps of about 2 eV indicate that both compounds are semiconductors.
High‐Pressure Synthesis and Crystal Structure of the Structurally New Orthorhombic Rare‐Earth Meta‐Oxoborates γ‐RE(BO2)3 (RE = La ‐ Nd)
Authors: Emme Holger , Despotopoulou Christina , Huppertz Hubert
Published: October 2004

The new meta‐oxoborates γ‐RE(BO2)3 (RE = La ‐ Nd) (≡ REB3O6) were obtained as colourless (La, Ce), light green (Pr) and pale violet (Nd) crystalline powders by the reaction of CeO2, Pr6O11, or RE2O3 (RE = La, Nd) and B2O3 in a Walker‐type multianvil apparatus under high‐pressure/high‐temperature conditions of 7.5 GPa and 1000 °C. The single crystal X‐ray structure determination of γ‐Ce(BO2)3 revealed: Pca21, a = 1845.7(2), b = 446.8(2), c = 429.5(2) pm, Z = 4, R1 = 0.0265, wR2 = 0.0451 (all data). For the isotypic compounds γ‐RE(BO2)3 (RE = La, Pr, Nd) the corresponding lattice parameters were obtained from powder data. Structurally, the compounds represent a new type of rare‐earth meta‐oxoborate RE(BO2)3 in addition to the well characterized monoclinic (RE = La ‐ Nd, Sm ‐ Lu; C2/c) and orthorhombic (RE = Tb ‐ Lu; Pnma) phases. Considering the increasing number of polymorphs, we introduced greek letter prefixes to the rare‐earth meta‐oxoborates, labeling the former known monoclinic phases as α‐RE(BO2)3 (space group: C2/c), the orthorhombic phases as β‐RE(BO2)3 (space group: Pnma), and the here presented orthorhombic phases as γ‐RE(BO2)3. Furthermore, we report about temperature‐resolved in‐situ powder‐diffraction measurements, and IR‐spectroscopic investigations into γ‐Ce(BO2)3.
From Gallium Hydride Halides to Molecular Gallium Sulfides
Authors: Schmidbaur Hubert , Nogai Stefan D.
Published: October 2004

Complexes of the type (L)GaHCl2, with L = tertiary phosphines or pyridines, have been prepared from (HGaCl2)2 and the ligands in diethyl ether. The products are stable crystalline solids soluble in common organic solvents. The presence of the Ga‐H function has been confirmed by IR and NMR spectroscopy and by single crystal X‐ray diffraction, carried out for the 1:1 adducts with L = PCy3 and PPh3 (two polymorphs) and for the 2:1 adduct with L = (CH2PPh2)2 (dppe, two different solvates). The reaction of PVi3 with (HGaCl2)2 gives an insoluble polymer owing to the hydrogallation of vinyl groups by the gallium hydride units (no Ga‐H functions are left in the product).Treatment of the complexes (R3P)GaHCl2 with H2S, metal sulfides or (Me3Si)2S gave only insoluble, ill‐defined products.‐ The 1:1 adduct (L′)GaHCl2, with L′ = 4‐dimethylamino‐pyridine, reacts with (Me3Si)2S in acetonitrile at ambient temperature to give an only partially sulfur‐substituted product of the net formula (L′)GaSH0.66Cl0.34. With excess ligand L′, under reflux conditions and after longer reaction times, a pyridine complex of the tetranuclear, molecular gallium sulfide Ga4S6 is obtained in low yield. The core of the compound with the composition (L′)4Ga4S6 has an adamantane structure resembling a cluster unit of the binary gallium sulfide polymorphs Ga2S3. The edge‐sharing Ga3S3 six‐membered rings are all in a chair conformation as found previously for the pyridine complexes of the ternary compounds [(L)GaEX]3(with E = S, Se and X = Cl, Br) and for the bicyclic dication [(L)6Ga4S5]2+. Thermolysis and degradation under mass spectrometry conditions lead to sublimation of L′ and leave amorphous Ga2S3. The reaction of (L′)GaCl3 with (Me3Si)2S did not afford any molecular gallium sulfide complex. A comparison of the structural data for (L′)GaCl3 and (L′)4Ga4S6 suggests a much poorer acceptor character of the gallium sulfide cluster.
Chemischer Transport ternärer Cobaltmolybdate — Experimente und Modellrechnungen
Authors: Steiner Udo , Daminova Sofia , Reichelt Werner
Published: October 2004

Der Chemische Transport der Phasen im System Co/Mo/O mit den Transportmitteln Cl2 und Br2 wurde im Temperaturgefälle 1173 nach 1073 K untersucht, wobei Einkristalle von Co2Mo3O8, CoO, Co3O4 und Co dargestellt werden konnten, während die abgeschiedenen CoMoO4‐Einkristalle aufgrund einer Phasenumwandlung bei etwa 660 K beim Abkühlen auf Raumtemperatur zerfallen. Ausgangsmaterial waren sowohl phasenreine Proben der ternären Verbindungen als auch Gemenge dreier koexistierender Phasen aus den unterschiedlichen Koexistenzgebieten des Systems. Das beobachtete Transportverhalten wird verglichen mit den Resultaten von Modellrechnungen zum Chemischen Transport und in Abhängigkeit von Ausgangsbodenkörperzusammensetzung, Transportmittelmenge und Feuchtigkeitsgehalt der Ampulle ausführlich diskutiert.
Kupferkomplexe von invers polarisierten Phosphaalkenen RP=C(NMe2)2 (R = t‐Bu, Ph). Molekülstruktur von [Cu3Cl3{μ‐P(t‐Bu)C(NMe2)2}3]
Authors: Weber Lothar , Krümberg Jens , Stammler Hans‐Georg , Neumann Beate
Published: October 2004

Die Reaktion äquimolarer Mengen des invers polarisierten Phosphaalkens t‐BuP=C(NMe2)2 (1) und Kupfer(I)chlorid liefert den Komplex [Cu3Cl3{μ‐P(t‐Bu)C(NMe2)2}3] (2) als formales Ergebnis der Cyclotrimerisierung eines 1:1‐Addukts. Analog wird der Komplex [Cu3Cl3{μ‐P(Ph)C(NMe2)2}3] (4) aus dem Phosphaalken PhP=C(NMe2)2 (3) und [Cu{P(OMe)3}3Cl] gewonnen. Die Verbindungen 2 und 4 wurden auf elementaranalytischem und spektroskopischem Weg (1H, 13C{1H}, 31P{1H}‐NMR) charakterisiert. Die Molekülstruktur von 2 wurde durch eine Röntgenstruktur ermittelt.
Schiff Base Formation upon Complexation of Tris(acetylacetonato)iron with N[(CH2CH2NH2)(CH2CH2OH)(CH2CH2CH2OH)]
Authors: Hahn F. Ekkehardt , Jocher Christoph , Lügger Thomas , Pape Tania
Published: October 2004

The reaction of the unsymmetrical aliphatic tripodal ligand N[(CH2CH2NH2)(CH2CH2OH)(CH2CH2CH2OH)] (H4‐3) with tris(acetylacetonato)iron(III) gives the dinuclear bis(μ‐alkoxo) bridged complex [Fe{N(CH2CH2N=C(CH3)CHC(CH3)O)‐ (CH2CH2CH2O)(CH2CH2O)}]2 [Fe(η5, μ‐4)]2 (5). The new ligand 43‐ is obtained by reaction of the primary amine function of H4‐3 with one of the acetylacetonato ligands under imine formation. The iron atoms in complex 5 are coordinated in an octahedral fashion within an N2O4 environment. Complex 5 contains three different alkoxo donor groups.
Fluoromanganat(III)‐Anionen mit neuer tetramerer und Kettenstruktur in (pipzH2)3[Mn4F18(H2O)]·(H2O) und (pipzH2)4[Mn2F9]2[MnF4(H2O)2][MnF4(HF)2]
Authors: Stief Ronald , Massa Werner
Published: October 2004

Bei systematischen Fällungsversuchen aus flußsauren Lösungen von MnIII und Piperazin konnten u.a. die beiden Titelverbindungen in reiner Form erhalten und ihre Kristallstrukturen röntgenographisch bestimmt werden. (pipzH2)3[Mn4F18(H2O)]·(H2O) kristallisiert orthorhombisch in Raumgruppe Pnma, Z = 4, a = 2050.8(2), b = 1253.0(1), c = 1096.0(1) pm, R = 0.0290. Die Struktur enthält ein neues tetrameres Anion [Mn4F18(H2O)]6‐ aus zwei über eine gemeinsame Ecke verbundenen kantenverknüpften Doppeloktaedern. (pipzH2)4[Mn2F9]2[MnF4(H2O)2][MnF4(HF)2] ist triklin, Raumgruppe $P{\bar 1}$, Z = 1, a = 901.6(1), b = 913.1(1), c = 1308.9(1) pm, α = 70.024(6)°, β = 75.229(6)°, γ = 78.887(6)°. Hier sind analoge Doppeloktaeder mit reiner Fluorkoordination zu Ketten verknüpft. Diese sind durch starke H‐Brücken F···H···F, O···H···F und N···H···F über isolierte oktaedrische Baugruppen [MnF4(H2O)2]‐ und [MnF4(HF)2]‐ sowie die (pipzH2)2+‐Kationen zu einem 3D Netz verbunden. Typisch in beiden Strukturen ist eine starke Oktaederstreckung durch den Jahn‐Teller‐Effekt, wobei die gestreckten Achsen parallel in der Ebene der Doppelverbrückung liegen, so daß beide Mn—F—‐Mn—Brücken stark asymmetrisch sind. Die Ordnung zwischen den Dimeren ist jedoch im Tetramer ferrodistortiv, im Kettenanion antiferrodistortiv.
The Cube‐Shaped Main Group Element Clusters (Bi4S4)4+ and (Bi4Se4)4+ ‐ Synthesis from Chloroaluminate Melts, Crystal Structures and Vibrational Spectra
Authors: Beck Johannes , Schlüter Stefan , Zotov Nicolay
Published: October 2004

The reaction of bismuth and bismuth trichloride with sulfur or selenium, respectively, in a AlCl3/NaCl melt at 130 °C leads to (Bi4S4)[AlCl4]4 1 and (Bi4Se4)[AlCl4]4 2 in the form of red and amber colored crystals. Both crystallize isotypically in the tetragonal space group $I{\bar 4}$ with the lattice constants a = 1181.60(2), c = 1104.75(2) pm for 1 and a = 1199.32(2), c = 1118.64(3) pm for 2. Besides the nearly regular tetrahedral [AlCl4]‐ ions the structures contain (Bi4S4)4+ and (Bi4Se4)4+ cations. These ions are actually of crystallographic S4 symmetry but deviate only slightly from the ideal cubic symmetry. Bi and chalcogen atoms occupy alternatingly the corners of the cubes. 1 and 2 are isotypical to the already known (Bi4Te4)[AlCl4]4, so the series of the cube‐shaped (Bi4E4)4+ ions (E = S, Se, Te) is now complete. Infrared und Raman spectra of 1 und 2 show the vibration modes of both kinds of ions in the region 50 ‐ 600 cm‐1. Symmetry analysis and normal mode calculations of the vibrational spectra confirm the local symmetry of the (Bi4E4) clusters and the [AlCl4] groups.
Carbomolybdate(III): Zur Kenntnis von Pr2[Mo2C3] sowie Strukturbeziehungen zu Er2Mo2C3
Authors: Dashjav Enkhtsetseg , Kreiner Guido , Schnelle Walter , Wagner Frank R. , Kniep Rüdiger
Published: October 2004

Pr2[Mo2C3] wurde durch Reaktion der Elemente im Lichtbogenofen und anschließenden Wärmebehandlung in gasdicht verschweißten Mo‐Ampullen bei 1500 °C hergestellt. Die Charakterisierung der Verbindung erfolgte über chemische Analysen, Röntgenbeugungsexperimente und metallographische Verfahren. Pr2[Mo2C3] kristallisiert (monoklin, P21/c, Z = 4, a = 597.99(10) pm, b = 665.15(11) pm, c = 1185.60(19) pm und β = 111.631(5)°) in einem neuen Strukturtyp. Die Kristallstruktur enthält ein dreidimensional verknüpftes Polyanion [(Mo2C3)6‐], in dem Molybdän(III) verzerrt tetraedrisch von Carbo‐Liganden umgeben ist. Tetramere Einheiten Mo4C10 aus kantenverknüpften MoC4‐Tetraedern bilden parallel (100) verlaufende Schichtverbände, die entlang [100] über gemeinsame Carbo‐Liganden (Spitzenverknüpfung der MoC4‐Tetraeder) miteinander verbunden sind. Die Umgebungen der Seltenerd‐Kationen entsprechen stark verzerrten (PrC5)‐Koordinationspolyedern (einfach überkappte Tetraeder und tetragonale Pyramiden). Die Metallatome bilden gemeinsam das Motiv einer verzerrten, kubisch innenzentrierten Anordnung; die Carbo‐Liganden besetzen bei dieser Beschreibung einen Teil der Oktaederlücken. Strukturchemisch ist Pr2[Mo2C3] eng verwandt mit Er2Mo2C3 (isotyp mit Ho2Mo2C3). Beide Strukturtypen gehören zu einer (hypothetischen) Abfolge von Kristallstrukturen der gemeinsamen Summenformel RE2[T2C3]. Die physikalischen Eigenschaften der neuen ternären Verbindung entsprechen denen eines schlechten Metalls („bad metal”︁) mit lokalisierten magnetischen 4f‐Momenten, in Übereinstimmung mit dem Vorliegen von Pr3+‐Spezies. Eine detaillierte Analyse der chemischen Bindung über Zustandsdichten (DOS) und die COHP‐Methode rechtfertigt die Beschreibung der Titelverbindung als Carbomolybdat(III).
Enthalpy Landscapes of the Earth Alkaline Metal Oxides
Authors: Schön J. C.
Published: October 2004

Recent developments in the field of solid state synthesis have given us access to synthesis conditions that range from effective negative pressures of about ‐1 GPa to high positive values exceeding 10 or even 100 GPa. Thus, it becomes necessary to explore not only the landscape of potential energy, but also the enthalpy landscapes for a wide range of pressures when attempting to predict possible crystalline modifications in a chemical system. In this work, we present the enthalpy landscapes for the earth alkaline oxides. The results are compared with experimental and theoretical studies, and we predict that it should be possible to synthesize at least some of these compounds in the so‐called 5‐5 modification.
Na8[B12(BSe3)6]: A Novel Selenoborato‐closo‐dodecaborate
Authors: Hammerschmidt A. , Döch M. , Pütz S. , Krebs B.
Published: October 2004

Systematic studies on selenoborates containing a B12 cluster entity and alkali metal cations led to the new crystalline phase Na8[B12(BSe3)6] which consists of a icosahedral B12 cluster completely saturated with trigonal‐planar BSe3 units and sodium counter‐ions. The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C. Na8[B12(BSe3)6] crystallizes in the monoclinic space group P21/c (no. 14) with a = 10.990(1) Å, b = 16.279(1) Å, c = 11.490(1), β = 117.82(1)° and Z = 2.
X‐Ray and Transmission Electron Microscopy Investigations of the New Solids In5S5Cl, In5Se5Cl, In5S5Br, and In5Se5Br
Authors: Deiseroth Hans‐Jörg , Reiner Christof , Xhaxhiu Kledi , Schlosser Marc , Kienle Lorenz
Published: October 2004

The compounds In5Ch5X (Ch = S, Se; X = Cl, Br) represent new mixed valence solids with indium occurring simultaneously in three different oxidation states: In+, In3+ and In2+ where the latter appears as covalently bonded dumbbells (In2)4+. Although the ionic formulation (In5Ch5X = In+ 2In3+ (In2)4+ 5Ch2— X—) is the same for all compounds, they crystallise in two structure types (In5Ch5Cl‐type: monoclinic, P21/m, Z = 2; In5Ch5Br‐type: orthorhombic, Pmn21, Z = 2). Ignoring the distribution of the halogen atoms, the anionic partial structure is very similar in both structure types. The main difference is an exchange of (In+) by (In2)4+ and vice versa on selected positions. This is possible due to the nearly identical coordination of both ions (tri‐capped trigonal prisms). HRTEM investigations show remarkable differences in the real structures of In5Ch5Cl and In5Ch5Br. In contrast to the perfectly ordered crystals of the bromides, the chlorides exhibit a variety of nanoscaled crystal defects, i.e. twinning, polylamellar intergrowth of polymorphs and lamellar intergrowth of structurally related compounds as demonstrated in In5S5Cl/In6S7. The occurrence of these defects is discussed using an appropriate structure model.
Synthese und Strukturen neuer Eisen‐Sauerstoff‐Alkoxid‐Cluster
Authors: Veith Michael , Grätz Frank , Huch Volker , Gütlich Philipp , Ensling Jürgen
Published: October 2004

Der Eisen‐Sauerstoff‐Alkoxy‐Cluster [Fe9O3(OC2H5)21]·C2H5OH kann unter unterschiedlichen Bedingungen zu Molekülen umgesetzt werden, denen alle die allgemeine Formel [Fe5O(OR)8(OR′)5] gemeinsam ist. Erwärmt man [Fe9O3(OC2H5)21]·C2H5OH in Toluol, so entsteht [Fe5O(OC2H5)13], das durch Kristallisation abgetrennt werden kann, wohingegen ein Auflösen von [Fe9O3(OC2H5)21]·C2H5OH in tert‐Butylamin zum 1 : 2‐Addukt [Fe5O(OC2H5)13]·2 t‐Bu‐NH2 führt. Mit Triethyl‐ oder Triphenylsilanol entsteht aus [Fe9O3(OC2H5)21]·C2H5OH wieder ein Sauerstoff‐Eisencluster des gleichen Motivs: [Fe5O(OC2H5)8{OSi(C2H5)3}5] bzw. [Fe5O(OC2H5)8{OSi(C6H5)3}5]. Die Molekülstruktur [Fe5O(OC2H5)8{OSi(C2H5)3}5], die über Röntgenbeugung an Einkristallen erhalten wird, besteht aus einem Grundgerüst, das aus einer Sauerstoff‐zentrierten quadratischen Fe5‐Pyramide besteht, wobei alle Kanten der Pyramide mit acht O‐C2H5 Gruppen überbrückt sind. Die terminalen Liganden an den Eisenatomen bestehen ausschließlich aus Triethylsiloxat‐Gruppen. Die Addition von zwei tert‐Butylamin Molekülen zu [Fe5O(OC2H5)13] hat einen drastischen Effekt auf die Molekül‐Struktur in [Fe5O(OC2H5)13]·2 t‐Bu‐NH2: in diesem Molekül sind alle Eisenatome verzerrt oktaedrisch koordiniert. Setzt man Eisen(III)‐chlorid mit Natriumethylalkoholat und Natrium‐tert‐butylat um, so bildet sich die Verbindung [Fe5O(OC2H5)8{OC(CH3)3}4Cl], deren innerer Eisen‐Sauerstoff‐Cluster denjenigen der anderen Moleküle ähnelt. Das Mößbauer‐Spektrum von [Fe5O(OC2H5)8{OSi(C6H5)3}5] enthält, wie erwartet, zwei Arten von Eisenatomen im Verhältnis 4 : 1. Bei einer Temperatur von 5 K wurde der Gesamtspin des Clusters zu S = 5/2 bestimmt. Dieser resultiert allein aus dem Spinzustand S = 5/2 des Eisenatoms in der Spitze der Pyramide, während die anderen vier äquivalenten Eisenatome der Fe4(OEt)4 Einheit antiferromagnetisch zu S = 0 gekoppelt sind.
Laser Zone Melting and Texture Formation in MgO‐doped Bi2.03Sr1.93Ca1.07Cu2.05O8+δ
Authors: Lennikov V. V. , Kazin P. E. , Tretyakov Yu. D. , de la Fuente Germán F.
Published: October 2004

The Laser Zone Melting (LZM) method was used to produce pure and MgO‐doped, textured Bi2.03Sr1.93Ca1.07Cu2.05O8+δ superconducting flat monoliths. Grain alignment was studied by XRD on the surface of both textured products as a function of annealing time and MgO content. Grain angle boundaries were found in all cases to be below 10° on the surface of all samples. Phase formation was studied during annealing after LZM, suggesting that formation of the 2212 phase takes place at faster rates in samples containing MgO. AC Magnetic Susceptibility studies were performed on annealed samples in order to determine Tc and Jc values. The transition temperatures remained approximately constant, while the critical current density values increased by a factor of 3 when MgO was present.