The [U2F12]2− Anion of Sr[U2F12]

The D_2h‐symmetric dinuclear complex anion [U₂F₁₂]^2? of pastel green Sr[U₂F₁₂] shows a hitherto unknown structural feature: The coordination polyhedra around the U atoms are edge‐linked monocapped trigonal prisms, the U^V atoms are therefore seven‐coordinated. This leads to a U–U distance of 3.8913(6) Å. A weak U^V–U^V interaction is observed for the dinuclear [U₂F₁₂]^2? complex and described by the antiferromagnetic exchange J_exp of circa ?29.9 cm^?1. The crystalline compound can be easily prepared from SrF₂ and β‐UF₅ in anhydrous hydrogen fluoride (aHF) at room temperature. It was studied by means of single crystal X‐ray diffraction, IR, Raman and UV/VIS spectroscopy, magnetic measurements, and by molecular as well as by solid‐state quantum chemical calculations.     

Indyllithium and the Indyl Anion [InL]−: Heavy Analogues of N‐Heterocyclic Carbenes

Reduction of the indate complex In(NON^Ar)(μ‐Cl)₂Li(OEt₂)₂ (NON^Ar=[O(SiMe₂NAr)₂]^2?; Ar=2,6‐iPr₂C₆H₃) with sodium generates the In^II diindane species [In(NON^Ar)]₂. Further reduction with a mixture of potassium and [2.2.2]crypt affords the In^I N‐heterocyclic indyl anion [In(NON^Ar)]^?, which crystallizes with a non‐contacted [K([2.2.2]crypt)]⁺ cation. The indyl anion can also be isolated as the indyllithium compound In(NON^Ar)(Li{THF}₃), which contains an In?Li bond. Density functional theory calculations show that the HOMO of the indyl anion is a metal‐centred lone pair, and preliminary reactivity studies confirm its nucleophilic behaviour.     

Photocontrolled Release of Chemicals from Nano‐ and Microparticle Containers

A benzoin‐derived diol linker was synthesized and used to generate biocompatible polyesters that can be fully decomposed on demand upon UV irradiation. Extensive structural optimization of the linker unit was performed to enable the defined encapsulation of diverse organic compounds in the polymeric structures and allow for a well‐controllable polymer cleavage process. Selective tracking of the release kinetics of encapsulated model compounds from the polymeric nano‐ and microparticle containers was performed by confocal laser scanning microscopy in a proof‐of‐principle study. The physicochemical properties of the incorporated and released model compounds ranged from fully hydrophilic to fully hydrophobic. The demonstrated biocompatibility of the utilized polyesters and degradation products enables their use in advanced applications, for example, for the smart packaging of UV‐sensitive pharmaceuticals, nutritional components, or even in the area of spatially selective self‐healing processes.     

Time-resolved thermoreflectivity of thin gold films and its dependence on film thickness

\valunit{10}{nm} to have been measured by femtosecond time-resolved pump-probe experiments. A conspicuous change of the relaxation behavior was found around for pump pulse fluences of . Thicker films show a nearly exponential decay of the transient linear reflectivity, which turns into a linear decay during the first for films with thicknesses of or less. This observation is evidence of a mean free path of about for hot electrons with temperatures around . Received: 17 December 1996     

Syntheses and Crystal Structures of a Series of Manganese-Lanthanide-Sodium 12-Metallacrown-4 Dimers

A series of heterotrimetallic manganese-lanthanide-sodium dimer metallacrowns has been synthesized and characterized by single-crystal X-ray analysis: {LnNa[12-MC_{Mn(III)N(shi)}-4]}₂(iph)₄, where Ln^III?=?La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), and Y (15); MC is metallacrown; shi^3? is salicylhydroximate; and iph^2? is isophthalate. The manganese(III) ions and shi^3? ligands generate the 12-MC-4 framework with one Ln^III and Na⁺ ion bound to each [12-MC_{Mn(III)N(shi)}-4] on opposite sides of the central MC cavity. The carboxylate groups of the isophthalate ligands bridge between the central Ln^III ion and each ring Mn^III ion, and the meta-arrangement of the carboxylate groups joins two LnNa[12-MC_{Mn(III)N(shi)}-4] units together to form the dimer through the Ln^III ions, which reside on the interior of the molecule. The identity of the central Ln^III ion slightly impacts the size the [12-MC_{Mn(III)N(shi)}-4] framework. As the crystal radius of the Ln^III ion increases from Lu^III (1.02 Å) to La^III (1.19 Å), the 12-MC-4 framework expands to accommodate the larger Ln^III ion as the MC cavity increases in size (0.53 Å for Lu^III to 0.58 Å for La^III) and the average cross cavity Mn^III-Mn^III and oxime oxygen-oxime oxygen distances also increase (Mn^III-Mn^III distances: 6.48 Å for Lu^III to 6.52 Å for La^III; O_oxime-O_oxime distances: 3.66 Å for Lu^III to 3.75 Å for La^III). In addition, the larger Ln^III ions reside further from the MC cavity as indicated by the Ln^III-oxime oxygen mean plane (O_oxMP) distance. The Ln^III-O_oxMP distance steadily decreases from La^III (1.7527(12) Å) to Lu^III (1.5575(15) Å).

Graphic Abstract

The complex {LaNa[12-MC_{Mn(III)N(shi)}-4]}₂(iph)₄(DMF)₆(H₂O)₂ is a dimer of [12-MC-4] molecules linked by four isophthalate anions

     

Acyclic 1,4-stereocontrol via reductive 1,3-transpositions

One-pot reduction/allylic diazene rearrangement of lactic acid- and mandelic acid-derived alpha,beta-unsaturated tosyl hydrazones leads to 1,4-syn- or 1,4-anti-E-2-alkenyl arrays in high yield and diastereoselectivity. Either the syn or the anti diastereomer can be prepared by choosing the appropriate alkene stereoisomer of the hydrazone. The E-alkenes led to the 1,4-syn isomers, while the Z-alkenes led to the 1,4-anti isomers, both with > or =20:1 diastereoselectivity.     

Preparation of cyclophanes by room-temperature ring-closing alkyne metathesis with imidazolin-2-iminato tungsten alkylidyne complexes

Room-temperature ring-closing alkyne metathesis of 1,2-, 1,3-, and 1,4-bis(3-pentynyloxymethyl)benzenes has been investigated in the presence of catalytic amounts of an imidazolin-2-iminato tungsten alkylidyne complex. The m- and p-diynes selectively form the respective [10]metacyclophane or [10.10]paracyclophane, respectively, whereas a mixture of monomeric and dimeric cycloalkynes is obtained in the case of the o-diyne. DFT calculations reveal that the different selectivities can be attributed to the relative thermodynamic stability of the emerging cyclophanes.     

Gamma limit of the nonself-dual Chern-Simons-Higgs energy

We consider the Gamma limit of the Abelian Chern-Simons-Higgs energy

     

Invariant measures and maximal L2 regularity for nonautonomous Ornstein-Uhlenbeck equations

We characterize the domain of the realizations of a linear parabolicoperator defined in L² spaces with respect to a suitable measurethat is invariant for the associated evolution semigroup. Asa byproduct, we obtain optimal L² regularity results for evolutionequations with time-dependant Ornstein–Uhlenbeck operators.