Christoph Wölper

Synthesis and characterization of heteroleptic 1-tris(pyrazolyl)borate beryllium complexes.

The synthesis and crystal structures of 1-tris(pyrazolyl)borate beryllium halides TpBeX (X = Cl 1, Br 2, I 3, F 4), the pyrazole adduct of TpBeF (5) and of 1-tris(pyrazolyl)borate beryllium hydride, deuteride and azide TpBeX (X = H 6, (2)H (D) 7, N3 8; Tp = 1-trispyrazolylborate) is described. In addition, (9)Be-NMR spectroscopy is introduced as suitable analytical tool for the in situ characterization of heteroleptic organoberyllium halides, pseudohalides and hydrides. Studies in different solvents and solvent mixtures allowed the formulation of a reference guide for the chemical shift of heteroleptic coordination complexes of beryllium only based on variation of the second substituent.

Temperature-Dependent Electron Shuffle in Molecular Group 13/15 Intermetallic Complexes†

Monovalent RAl (R=HC[C(Me)N(2,6-iPr2C6H3)]2) reacts with E2Et4 (E=Sb, Bi) with insertion into the weak E-E bond and subsequent formation of RAl(EEt2)2 (E=Sb 1; Bi 2). The analogous reactions of RGa with E2Et4 yield a temperature-dependent equilibrium between RGa(EEt2)2 (E=Sb 3; Bi 4) and the starting reagents. RIn does not interact with Sb2Et4 under various reaction conditions, but formation of RIn(BiEt2)2 (5) was observed in the reaction with Bi2Et4 at low temperature.

An azobenzene unit embedded in a cyclopeptide as a type-specific and spatially directed switch.

By embedding an azobenzene unit into a chiral scaffold, switching of azobenzene from the trans-(P) isomer to the cis-(P) isomer and back was achieved (black arrows in picture). The embedding leads to a flipping process in which the phenyl rings can only move directly towards one another in the switching process.

Synthesis and Structural Characterization of Magnesium‐Substituted Polystibides [(LMg)4Sb8]

Redox reactions of [(L(1,2) Mg)2 ] and Sb2 R4 (R=Me, Et) yielded the first Mg-substituted realgar-type Sb8 polystibides [(L(1,2) Mg)4 (μ4 ,η(2:2:2:2) -Sb8)] (L(1) =HC[C(Me)N(2,4,6-Me3 C6 H2)]2, L(2) =HC[C(Me)N(2,6-i-Pr2 C6 H3)]2). Compounds [(L(1,2) Mg)2] serve both as reducing agents, initiating the cleavage of the Sb-C bonds, and as stabilizers for the resulting Sb8 polyanion. The polystibides were characterized by NMR and IR spectroscopies, elemental analysis, and X-ray structure analysis. In addition, results from quantum chemical calculations are presented.

A Gallium-Substituted Distibene and an Antimony-Analogue Bicyclo[1.1.0]butane: Synthesis and Solid-State Structures.

RGa {R=HC[C(Me)N(2,6-iPr2C6H3)]2} reacts with Sb(NMe2)3 with insertion into the Sb-N bond and elimination of RGa(NMe2)2 (2), yielding the Ga-substituted distibene R(Me2N)GaSb=SbGa(NMe2 )R (1). Thermolysis of 1 proceeded with elimination of RGa and 2 and subsequent formation of the bicyclo[1.1.0]butane analogue [R(Me2N)Ga]2Sb4 (3).

Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence

Here we report on a novel system based on aromatic thioethers with unique luminescence properties. Fifteen different compounds were investigated in detail on their luminescence properties using UV/Vis absorption and steady-state and time-resolved luminescence spectroscopy. Excited state lifetimes as well as quantum yields were determined, and the toxicity towards HeLa cells was investigated. Besides X-ray analyses also quantum chemical calculations were performed to gain deeper insights in the unique behavior of this facile system. The studied compounds reveal remarkable fluorescence emission ranging from 437 to 588 nm as well as phosphorescence (up to 5 μs).

Reduction of [Cp*Sb]4 with Subvalent Main-Group Metal Reductants: Syntheses and Structures of [(L1Mg)4(Sb4)] and [(L2Ga)2(Sb4)] Containing Edge-Missing Sb4 Units

[Cp*Sb]4 (Cp*=C5 Me5 ) reacts with [L1 Mg]2 and L2 Ga with formation of [(L1 Mg)4 (μ4 ,η1:2:2:2 -Sb4 )] (L1 =iPr2 NC[N(2,6-iPr2 C6 H3 )]2 , 1) and [(L2 Ga)2 (μ,η2:2 -Sb4 )] (L2 =HC[C(Me)N(2,6-iPr2 C6 H3 )]2 , 2). The cleavage of the Sb-Sb and Sb-C bonds in [Cp*Sb]4 are the crucial steps in both reactions. The formation of 1 occurred by elimination of the Cp* anion and formation of Cp*MgL1 , while 2 was formed by reductive elimination of Cp*2 and oxidative addition of L2 Ga to the Sb4 unit. 1 and 2 were characterized by heteronuclear NMR spectroscopy and single-crystal X-ray diffraction, and their bonding situation was studied by quantum chemical calculations.

Light and Chemically Driven Molecular Machines Showing a Unidirectional Four-State Switching Cycle

The imitation of macroscopic movements at the molecular level is a key step in the development of nanomachines. The challenge is the synthesis of molecules that are able to transform external stimuli into a direction-controlled mechanical movement. The more complex such motion sequences are, the more difficult is the construction of the corresponding nanomachine. Here, we present a system that demonstrates a unidirectional, four-state switching cycle that bears similar characteristics to the arm movements of a human breaststroke swimmer. Like the latter, the molecules have a torso and two arms. The arms consist of bipyridine units and can be folded and stretched by addition and removal of copper ions. The unidirectional rotation of the arms is achieved by light-induced switching of an azo unit.

Solid‐State Structure of Bromine Azide

Covalent azides have been investigated for more than hundred years. Hydrazoic acid (HN3) for instance was synthesized for the first time by Curtius in 1890. Since then, its molecular structure was investigated by use of IR and microwave spectroscopy as well as electron diffraction. Only very recently, Klapçtke et al. reported on the solid-state structure of the compound, which was determined by singlecrystal X-ray diffraction, showing that HN3 crystallizes in a two-layer structure in which almost planar layers, formed by intermolecular hydrogen bonds between the HN3 molecules, are stacked parallel to (001) with an ABA stacking sequence. Aside from HN3, the halogen azides XN3 (X = F, Cl, Br, I) are the simplest azides. They have been investigated experimentally and theoretically, in particular in respect to their bonding situation. IN3 was found to be monomeric in CFCl3 solution and forms a trans-bent structure in the gas phase. In contrast, in the solid state, IN3 adopts a polymeric structure, with disordered azide groups with almost identical I N bond distances (2.264(23), 2.30(3) ). Unfortunately, only IN3 has been structurally characterized by single-crystal Xray diffraction to date. The growth of suitable single crystals of halogen azides in general is difficult owing to their extreme sensitivity towards small pressure variations. For instance, bromine azide was reported to explode when Dp 0.05 Torr, and also upon crystallization. However, the gas-phase structure of BrN3, which adopts a trans-bent structure, could be determined by electron diffraction, and the experimental structure parameters agreed well with those obtained from quantum-chemical calculations. We became interested in the synthesis of covalent azides only recently, and reported on the solid-state structures of Group 15 triazides (Sb(N3)3, Pyr2Bi(N3)3), [11] a novel pentaazidoantimonite dianion (Sb(N3)5 2 ), and organoantimony diazides RSb(N3)2. [13] Herein, we expand these studies on the synthesis of halogen azides and present the single-crystal Xray structure of bromine azide, BrN3 (1). BrN3 (1) was prepared by reaction of NaN3 with bromine (Scheme 1). The N NMR spectrum of a solution of 1 in

A modular approach towards functional supramolecular aggregates - subtle structural differences inducing liquid crystallinity

Herein we report an efficient modular approach to supramolecular functional materials. Hierarchical self-assembly of azopyridine derivatives and hydrogen-bond donors yielded discotic assemblies. Subtle differences in the core units introduced mesomorphic behaviour and fast photo-response of the liquid crystals based on phloroglucinol. The presented results prove the benefits of a modular methodology towards highly responsive materials with tailor-made properties.