Difluorotetrakis(2‐oxypyridine)dirhenium(III) – Preparation,Crystallographic Structure,and Electrochemical Properties

The solid‐state‐melt reaction of (NH₄)₂[Re₂F₈] · 2H₂O with 2‐hydroxypyridine (2‐HOpy) produced dark‐red Re₂(2‐Opy)₄F₂ ( 1 ). This air‐stable compound was obtained in crystalline form as 1· CHCl₃. It was characterized in the solid state by single‐crystal X‐ray diffraction and in solution by UV/Vis spectroscopy and cyclic voltammetry. 1· CHCl₃ forms triclinic crystals with α = 8.3254(5) Å, b = 8.5563(5) Å, c = 11.6784(8) Å, α = 82.723(3)°, β = 75.769(3) °, γ = 64.407(2) °. The Re–Re and Re–F distances were 2.2091(7) and 2.115(6) Å, respectively. The molecule is isostructural with the corresponding chloro derivative.     

Nitrosyltechnetium(I) Complexes with 2‐(Diphenylphosphanyl)aniline

[Tc^I(NO)Cl(H₂L1)₂]⁺ cations (H₂L1 = 2‐(diphenylphosphanyl)aniline) are formed during reactions of H₂L1 with (NBu₄)[Tc(NO)Cl₄(MeOH)] or (NH₄)TcO₄/HCl/NH₂OH mixtures. Different isomers were isolated depending on the counterions and solvents used. The technetium(I) complexes cis‐NO,Cl,trans‐P,P‐[Tc^I(NO)Cl(H₂L1)₂]Cl, trans‐NO,Cl,cis‐P,P‐[Tc^I(NO)Cl(H₂L1)₂]₂(TcCl₆), and trans‐NO,Cl,trans‐P,P‐[Tc^I(NO)Cl(H₂L1)₂](PF₆) were isolated in crystalline form and studied by spectroscopic methods and X‐ray crystallography. DFT calculations show that there are only minor energy differences between the three isomers and the formation of the individual compounds is most probably strongly influenced by interactions with solvents and counterions.     

Synthese und Kristallstruktur der Molybdännitrido‐Komplexe [MoNCl3(MeCN)]4 und [MoNCl2(bipy)]4

Syntheses and Crystal Structures of the Nitrido Complexes [MoNCl₃(MeCN)]₄ and [MoNCl₂(bipy)]₄ [MoNCl₃(MeCN)]₄ ( 1 ) is obtained by the reaction of MoCl₄(MeCN)₂ with Me₃SiN₃ in CH₂Cl₂ as a sparingly soluble and water sensitive red compound. It crystallizes as 1 · 3 CH₂Cl₂ in the triclinic space group P 1 with a = 889.7(1), b = 1004.8(1), c = 1270.4(2) pm; α = 71.69(1)°; β = 73.63(1)°; γ = 86.32(1)°, and Z = 1. It forms centrosymmetric tetranuclear complexes, in which the Mo atoms are connected by asymmetric and linear nitrido bridges with distances Mo–N of 167.5 and 214.3 pm. The acetonitrile molecules are coordinated with a long bond length Mo–N of 241 pm in trans position to the Mo–N triple bond. The reaction of 1 with 2,2′‐bipyridine in CH₂Cl₂/THF yields the tetranuclear molybdenum(V) complex [MoNCl₂(bipy)]₄ ( 2 ) as main product. It crystallizes in the tetragonal space group P4₂/n with a = 1637.5(2), c = 1018.3(2) pm, and Z = 2. In the tetranuclear complexes with the symmetry S₄ linear and asymmetric nitrido bridges connect the Mo atoms to form an almost planar eight membered Mo–N ring with distances Mo–N of 173 and 203 pm. The bipyridine molecules coordinate as chelates in cis and trans position to the Mo–N triple bond. In this case the trans influence causes different Mo–N distances of 219 and 232 pm.     

Rhenium(V) and technetium(V) complexes with phosphoraneimine and phosphoraneiminato ligands

Air-stable rhenium(V) nitrido complexes are formed when [ReOCl3(PPh3)2], [NBu4][ReOCl4], or [NBu4][ReNCl4] are treated with an excess of silylated phosphoraneiminates of the composition Me3SiNPPh3 or Ph2P(NSiMe3)CH2PPh2 in CH2Cl2. Complexes of the compositions [ReNCl(Ph2PCH2PPh2NH)2]Cl (1), [ReN(OSiMe3)(Ph2PCH2PPh2NH)2]Cl (2) or [ReNCl2(PPh3)2] (3) were isolated and structurally characterized. The latter compound was also produced during a reaction of the rhenium(III) precursor [ReCl3(PPh3)2(CH3CN)] and Me3SiNPPh3. Nitrogen transfer from the phosphorus to the rhenium atoms and the formation of nitrido ligands were observed in all examples. All products of reactions with an excess of the potentially chelating phosphoraneiminate Me3SiNP(Ph2)CH2PPh2 contain neutral Ph2PCH2PPh2NH ligands. The required protons are supplied by a metal-induced decomposition of the solvent dichloromethane. The Re-N(imine) bond lengths (2.055-2.110 A) indicate single bonds, whereas the N-P bond with lengths between 1.596 A and 1.611 A reflect considerable double bond character. An oxorhenium(V) phosphoraneiminato complex, the dimeric compound [ReOCl2(mu-N-Ph2PCH2PPh2N)]2 (4), is formed during the reaction of [NBu4][ReOCl4] with an equivalent amount of Ph2P(NSiMe3)CH2PPh in dry acetonitrile. The blue neutral complex with two bridging phosphoraneiminato units is stable as a solid and in dry solvents. It decomposes in solution, when traces of water are present. The rhenium-nitrogen distances of 2.028(3) and 2.082(3) A are in the typical range of bridging phosphoraneiminates and an almost symmetric bonding mode. Technetium complexes with phosphoraneimine ligands were isolated from reactions of [NBu4][TcOCl4] with Me3SiNPPh3, and [NBu4][TcNCl4] with Me3SiNP(Ph2)CH2PPh2. Nitrogen transfer and the formation of a five-coordinate nitrido species, [TcNCl2(HNPPh3)2] (5), was observed in the case of the oxo precursor, whereas reduction of the technetium(VI) starting material and the formation of the neutral technetium(V) complex [TcNCl2(Ph2PCH2PPh2NH)] (6) or [TcNCl(Ph2PCH2PPh2NH)2]Cl (7) was observed in the latter case. Both technetium complexes are air stable and X-ray structure determinations show bonding modes of the phosphoraneimines similar to those in the rhenium complexes.     

Reactions of Rhenium and Technetium Nitrido Complexes with ER3 Fragments (E = B,Ga, Al,C, P; R = H,Alkyl, Aryl)

Terminal ‘N^3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used. Air‐stable compounds with Re≡N‐ER₃ bridges are formed when ER₃ is BR₃ (R = H, Cl, Br, Ethyl, Phenyl, C₆F₅), BCl₂Ph, GaCl₃, CPh₃⁺, or PPh₃. The six‐co‐ordinate rhenium(V) complexes [ReNX₂(PMe₂Ph)₃] (X = Cl, Br), [ReN(X)(Et₂dtc)(PMe₂Ph)₂] (Et₂dtc^— = diethyldithiocarbamate) and [ReN(Et₂dtc)₂(PMe₂Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl₂(PPh₃)₂], [ReN(Et₂dtc)₂], [ReN{Ph₂P(S)NP(S)Ph₂}₂] or [ReNCl₄]^— only react with the most reactive Lewis bases of the examples mentioned above such as BCl₂Ph or B(C₆F₅)₃. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors. Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms. EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d¹) [ReNX₄]^— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl₄]^— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge. The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH₃ and BPhCl₂ have been established.     

Hybrid composites of monodisperse pi-conjugated rodlike organic compounds and semiconductor quantum particles

Composite materials of quantum particles (Q-particles) arranged in layers within crystalline powders of pi-conjugated, rodlike dicarboxylic acids are reported. The synthesis of the composites, either as three-dimensional crystals or as thin films at the air-water interface, comprises a two-step process: 1) The preparation of the Cd salts 6 (Cd), 8 (Cd) or Pb salts 6 (Pb), 8 (Pb) of the oligo(p-phenyleneethynylene)dicarboxylic acids 6 (H), 8 (H), in which the metal ions are arranged in ribbons and are separated by the long axis of the organic molecules, as demonstrated by X-ray powder diffraction analysis of the solids and grazing incidence X-ray diffraction analysis of the films on water. 2) Topotactic solid/gas reaction of these salts with H(2)S to convert the metal ions into Q-particles of CdS or PbS embedded in the organic matrix that consists of the acids 6 (H) and 8 (H). These hybrid materials have been characterized by X-ray photoelectron spectroscopy and transmission electron microscopy.     

Tricarbonylrhenium(I) and -technetium(I) complexes with bis(2-pyridyl)phenylphosphine and tris(2-pyridyl)phosphine

(NEt₄)₂[Re(CO)₃Br₃] or (NEt₄)₂[Tc(CO)₃Cl₃] react with bis(2-pyridyl)phenylphosphine (PPhpy₂) or tris(2-pyridyl)phosphine (Ppy₃) under formation of neutral tricarbonyl complexes of the composition [M(CO)₃X(L)] (M = Re, X = Br; M = Tc, X = Cl; L = PPhpy₂ or Ppy₃). In all isolated products, the ligands coordinate solely via two of their nitrogen atoms. All attempts to force a tripodal coordination of the phosphinopyridines failed. Removal of the bromo ligands from (NEt₄)₂[Re(CO)₃Br₃] by the addition of AgNO₃ in THF/water, and subsequent reaction of the resulting [Re(CO)₃(THF)₃](NO₃)with Ppy₃ yielded the complex [Re(CO)₃(NO₃)(Ppy₃-N,N′)] with a monodentate coordinated nitrato ligand. The products have been characterized spectroscopically and by X-ray structure analyses.     

Über einen Mikro-Kühltisch und seine Anwendung

Zusammenfassung Auf Grund der Erfahrungen mit dem Mikro-Heiztisch wurde ein Mikro-Kühltisch hergestellt, der in seiner Handhabung einfach und jederzeit gebrauchsfähig ist. Die Kühlung erfolgt durch Verdampfen von flüssiger Kohlensäure. Eine daneben eingebaute elektrische Heizung ermöglicht es, auch den Bereich der Raumtemperatur nach beiden Richtungen mit beliebiger Geschwindigkeit zu durchschreiten. Der Apparat umfaßt einen Temperaturbereich von –55° bis +80°.Auf diesem Kühltisch lassen sich bei organischen und anorganischen Stoffen und Stoffgemischen alle Erscheinungen, die sich bei Temperaturänderungen bei und unterhalb Raumtemperatur abspielen, in analog einfacher Weise beobachten und leiten wie die entsprechenden Vorgänge oberhalb Raumtemperatur am Heiztisch. An einer Reihe von Beispielen werden folgende Untersuchungen beschrieben: Schmelz- und Erstarrungspunkte, eutektische bzw. kryohydratische Temperaturen, Polymorphieund Isomorphiebeziehungen, Nachweis von Molekülverbindungen, Übergangspunkte bei Hydraten, Auftreten stabilisierter Zwischenphasen, eutektische und quasi-eutektische Kristallisation, normale und anormale Abscheidungsfolge bei Unterkühlung und die damit zusammenhängende Erscheinung der Hofbildung.

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Summary On the basis of experience with the micro hot stage, a micro-cooling stage was constructed, which is simple in operation and ready for use at all times. The cooling is secured through vaporization of liquid carbon dioxide. A neighboring built-in electrical heater makes it possible also to pass through the region of room temperature in either direction with any desired speed. The apparatus has a temperature range from –55° to + 80°.On this cooling stage organic and inorganic materials and mixtures show all the phenomena, which occur at temperature changes at and below room temperature, and these may be observed in analogously simple fashion and controlled as in the case of the corresponding processes occurring at temperatures above room temperature on the hot stage. The following studies were described from a series of investigations: melting and solidification points; eutectic and cryohydric temperatures; polymorphic and isomeric relationships; detection of molecular compounds; transition points of hydrates; appearance of stable intermediate phases; eutectic and quasi-eutectic crystallization; normal and abnormal precipitation succession on supercooling and the related phenomena of halo formation.

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Résumé Sur la base des expériences avec la micro-table chauffante, on a préparé une micro-table réfrigérante, de manipulation simple et toujours prète pour l'emploi. Le refroidissement s'obtient en évaporant de l'anhydride carbonique liquide. Un chauffage électrique installé à côté permet de passer par la température ordinaire, dans les deux sens et avec une vitesse quelconque. L'appareil embrasse un domaine de température de –55° à +80°. A l'aide de cette table réfrigérante, on peut observer, dans les corps organiques et minéraux dans les mélanges, tous les phénomènes qui se produisent par changement de température à l'ambiante ou au-dessous. On peut diriger d'une manière simple et analogue à ce qui se passe sur la table chauffante, au-dessus de la température ordinaire, les processus correspondants. On décrit à l'aide de quelques exemples les expériences suivantes: points de fusion et de solidification, eutectiques ou températures cryohydratiques, relations de polymorphisme et d'isomorphisme, recherche des combinaisons moléculaires, point de transformation chez les hydrates, apparition de phases intermédiaires stables, cristallisation eutectique et quasi-eutectique suite de dépôts normaux et anormaux par sous-refroidissement et les phénomènes de halo qui en résultent.

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Mit 3 Abbildungen.     

Longitudinal brain imaging of five malignant glioma patients treated with bevacizumab using susceptibility-weighted magnetic resonance imaging at 7 T

Malignant glioma is a rare tumor type characterized by prominent vascular proliferation. Antiangiogenic therapy with the monoclonal antibody bevacizumab is considered as a promising therapeutic strategy, although the effect on tumor vascularization is unclear. High-field susceptibility-weighted imaging (SWI) visualizes the microvasculature and may contribute to the investigation of antiangiogenic therapy responses in gliomas. We prospectively studied five adult malignant glioma patients treated with bevacizumab-containing regimens. In each patient, we performed three 7-T SWI and T1-weighted imaging investigations (baseline and 2 and 4 weeks after the start of bevacizumab treatment). In addition, we imaged a postmortem brain of a patient with glioblastoma using 7-T SWI and performed detailed histopathological analysis. We observed almost total resolution of brain edema in three of five patients after initiation of bevacizumab therapy. In one case with rapid increase of the lesion size despite bevacizumab therapy, SWI showed progressive increase of irregular hypointense structures, most likely corresponding to increasing amounts of pathological microvasculature. In one case with progressive neurological decline, 7-T images showed multiple intratumoral microhemorrhages after the first bevacizumab application. Correlation of postmortem neuroimaging with histopathology confirmed that SWI-positive structures correspond to tumor vasculature. The experience from our case series indicates that longitudinal 7-T SWI seems to be an appropriate method for investigation of changes in brain tumor vascularization over time under antiangiogenic therapy.