Crystallography Aided by Atomic Core-Level Binding Energies: Proton Transfer versus Hydrogen Bonding in Organic Crystal Structures

Ionic bond or hydrogen bridge? Br?nsted proton transfer to nitrogen acceptors in organic crystals causes strong N1s core-level binding energy shifts. A study of 15 organic cocrystal and salt systems shows that standard X-ray photoelectron spectroscopy (XPS) can be used as a complementary method to X-ray crystallography for distinguishing proton transfer from H-bonding in organic condensed matter.     

Solution and solid-state interactions in a supramolecular ruthenium photosensitizer-polyoxometalate aggregate

The intermolecular interactions between a ruthenium-based photosensitizer ([Ru(tbbpy)(2)(biH(2))](2+)) and a molecular metal oxide ([β-Mo(8)O(26)](4-)) are investigated in solution and in the solid state. The supramolecular interactions were studied using (1)H-NMR, UV-Vis and emission spectroscopy, ESI mass spectrometry and single-crystal X-ray diffraction. The formation of supramolecular aggregates was observed both in the crystal lattice and in solution. In addition, it is shown that aggregation in solution can be controlled by the competitive formation of ion pairs.     

On the facets of the secondary polytope

The secondary polytope of a point configuration A is a polytope whose face poset is isomorphic to the poset of all regular subdivisions of A. While the vertices of the secondary polytope - corresponding to the triangulations of A - are very well studied, there is not much known about the facets of the secondary polytope.The splits of a polytope, subdivisions with exactly two maximal faces, are the simplest examples of such facets and the first that were systematically investigated. The present paper can be seen as a continuation of these studies and as a starting point of an examination of the subdivisions corresponding to the facets of the secondary polytope in general. As a special case, the notion of k-split is introduced as a possibility to classify polytopes in accordance to the complexity of the facets of their secondary polytopes. An application to matroid subdivisions of hypersimplices and tropical geometry is given.     

A real-time decision rule for an inventory system with committed service time and emergency orders

In this paper, we study the inventory system of an online retailer with compound Poisson demand. The retailer normally replenishes its inventory according to a continuous review (nQ, R) policy with a constant lead time. Usually demands that cannot be satisfied immediately are backordered. We also assume that the customers will accept a reasonable waiting time after they have placed their orders because of the purchasing convenience of the online system. This means that a sufficiently short waiting time incurs no shortage costs. We call this allowed waiting time “committed service time”. After this committed service time, if the retailer is still in shortage, the customer demand must either be satisfied with an emergency supply that takes no time (which is financially equivalent to a lost sale) or continue to be backordered with a time-dependent backorder cost. The committed service time gives an online retailer a buffer period to handle excess demands. Based on real-time information concerning the outstanding orders of an online retailer and the waiting times of its customers, we provide a decision rule for emergency orders that minimizes the expected costs under the assumption that no further emergency orders will occur. This decision rule is then used repeatedly as a heuristic. Numerical examples are presented to illustrate the model, together with a discussion of the conditions under which the real-time decision rule provides considerable cost savings compared to traditional systems.     

Diastereoselective synthesis of 6-functionalized 4-aryl-1,3-oxazinan-2-ones and their application in the synthesis of 3-aryl-1,3-aminoalcohols and 6-arylpiperidine-2,4-diones

Halocyclocarbamation of benzyl N-(1-phenyl-3-butenyl)carbamates afforded 6-functionalized 4-aryl-1,3-oxazinan-2-ones with moderate to excellent diastereoselectivity depending on the N-substituent. Importantly, in contrast to reported cyclocarbamations of homoallylic carbamates, which are generally trans-diastereoselective, cyclization of N-unsubstituted Cbz-protected homoallylamines led to cis-1,3-oxazinan-2-ones, predominantly. The use of N-benzylated and in situ prepared N-silylated derivatives resulted however in trans-selectivity. Transition states are proposed to explain the stereochemical influence of the N-substituent on the cyclocarbamations. The functionalized 1,3-oxazinan-2-ones could be further elaborated towards biologically or synthetically important 6-arylpiperidine-2,4-diones and 3-aryl-1,3-aminoalcohols.     

A concept to tailor electron delocalization: applying QTAIM analysis to phenyl-terpyridine compounds

To gain a deeper understanding of how structural modifications may influence photochemical properties of 4'-phenyl-2,2':6',2'-terpyridines, the investigations presented here focus on electron delocalization in 4'-phenyl-2,2':6',2'-terpyridine derivatives and their Ru(II) and Zn(II) complexes. In those systems of neighboring aromatic rings the considerable torsion between the rings is commonly regarded to be the limiting factor for a well pronounced π-conjugation between the rings. A common approach to improve the π-conjugation is to lower the steric hindrance, thus achieving a more planar geometry. Here, we present a fundamentally different approach towards enhanced π-conjugation by manipulation of the electronic properties of the pyridine-phenyl (py-ph) bond. This is accomplished by introducing various substituents at the phenylene moiety or coordinating the terpyridine moiety to transition metal ions. The electron delocalization was quantified via the DFT-calculated ellipticity in the bond-critical point (BCP) of the py-ph bond. This ellipticity can be modified due to substituents in the para position of phenylene and via the transition metals coordinated to the terpyridine moiety. Changes in electron density distribution induced by the substituents and the metal ions are further studied by means of intermolecular electron density difference plots. It was shown that a NH(2) group in the para position of the phenyl ring as well as the coordination to Ru(II) or Zn(II) ions significantly enhances the π-character of the py-ph bond. Surprisingly, an even higher π-character of the py-ph bond is achieved by introducing additional NH(2) groups in ortho position to the py-ph bond, despite the increased torsion between pyridine and phenylene. The introduction of other substituents (-NO(2), -Br, -CN, -vinyl, -ethynyl) studied within the presented work enables an actuation of the electron delocalization between terpyridine and phenylene. In doing so, the ellipticity is a concise quantity to characterize electron delocalization in the studied systems. Furthermore, the ellipticity in the BCP of the py-ph bond is related to the corresponding geometrical properties (e.g., bond length and dihedral angle) and to the DFT-calculated HOMO and LUMO energies.     

XPS investigations of thick,oxygen-containing cubic boron nitride coatings

Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen.