Resolution of chiral, tetrahedral M4L6 metal-ligand hosts

The supramolecular metal-ligand assemblies of M416 stoichiometry are chiral (M = GaIII, AlIII, InIII, FeIII, TiIV, or GeIV, H41 = N,N'-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene). The resolution process of delta delta delta delta- and lambda lambda lambda lambda-[M(4)1(6)]12- by the chiral cation S-nicotinium (S-nic+) is described for the Ga(III), Al(III), and Fe(III) assemblies, and the resolution is shown to be proton dependent. From a methanol solution of M(acac)3, H(4)1, S-nicI, and KOH, the delta delta delta delta-KH3(S-nic)7[(S-nic) subset M(4)1(6)] complexes precipitate, and the lambda lambda lambda lambda-K6(S-nic)5[(S-nic) subset M(4)1(6)] complexes subsequently can be isolated from the supernatant. Ion exchange enables the isolation of the (NEt4(+))(12), (NMe4(+))(12), and K+(12) salts of the resolved structures, which have been characterized by CD and NMR spectroscopies. Resolution can also be accomplished with 1 equiv of NEt4+ blocking the cavity interior, demonstrating that external binding sites are responsible for the difference in S-nic+ enantiomer interactions. Circular dichroism data demonstrate that the (NMe4(+))(12) and (NEt4(+))(12) salts of the resolved [Ga(4)1(6)]12- and [Al(4)1(6)]12- structures retain their chirality over extended periods of time (>20 d) at room temperature; heating the (NEt4(+))(12)[Ga(4)1(6)] assembly to 75 degrees C also had no effect on its CD spectrum. Finally, experiments with the resolved K(12)[Ga(4)1(6)] assemblies point to the role of a guest in stabilizing the resolved framework.     

Opportunities for measurements of astrophysical-relevant alpha-capture reaction rates at CRYRING@ESR

The heavy-ion storage ring CRYRING@ESR has recently been installed and commissioned at GSI as one of the first installations of the upcoming Facility for Antiproton and Ion Research (FAIR). It is designed to store highly charged ions in the energy range between 300 keV/u and about 10 MeV/u. It will incorporate a gas-jet target providing high-density jets of, among other gases, hydrogen and helium. This will allow to study alpha-capture reaction rates of astrophysical interest in the energy range of the Gamow window for core-collapse supernovae. Special interest comes from the long-lived radio-isotope ⁴⁴Ti (t_1/2 = 58.9 years), which is supposed to be produced in the alpha-rich freeze-out during such an event. The nucleosynthesis of this isotope is of great interest, as the amount of material produced can be estimated by direct observation in remnants of recent supernovae. The disagreements between the observations and the estimations from astrophysical models show the need of more experimental data for the production and consumption reactions in the energy range of a core-collapse supernova. In this article, we will describe the proposed method of injecting beams of ⁴⁴Ti into CRYRING@ESR and performing the actual reaction rate measurements.     

Microwave synthesis and inherent stabilization of metal nanoparticles in 1-methyl-3-(3-carboxyethyl)-imidazolium tetrafluoroborate

The synthesis of Co-NPs and Mn-NPs by microwave-induced decomposition of the metal carbonyls Co(2)(CO)(8) and Mn(2)(CO)(10), respectively, yields smaller and better separated particles in the functionalized IL 1-methyl-3-(3-carboxyethyl)-imidazolium tetrafluoroborate [EmimCO(2)H][BF(4)] (1.6 ± 0.3 nm and 4.3 ± 1.0 nm, respectively) than in the non-functionalized IL 1-n-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF(4)]. The particles are stable in the absence of capping ligands (surfactants) for more than six months although some variation in particle size could be observed by TEM.     

Emergence of a New [NNN] Pincer Ligand via Si−H Bond Activation and β-Hydride Abstraction at Tetravalent Cerium

The cerium(IV) pyrazolate complexes [Ce(Me₂pz)₄]₂ and [Ce(Me₂pz)₄(thf)] initiate β-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me₂pz)₃(bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me₂pz =3,5-dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si−H-bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me₂pz)₄]₂ is treated with [Li{N(SiMe₃)₂}], that is, in the absence of the SiH functionality, any redox chemistry did not occur. Instead, the ceric ate complex [LiCe₂(Me₂pz)₉] and the stable mixed-ligand ceric species [Ce(Me₂pz)₂{N(SiMe₃)₂}₂] were obtained.     

A note on scenario reduction for two-stage stochastic programs

We extend earlier work on scenario reduction by relying directly on Fortet-Mourier metrics instead of using upper bounds given in terms of mass transportation problems. The importance of Fortet-Mourier metrics for quantitative stability of two-stage models is reviewed and some numerical results are also provided.