Supramolecular Metallacycles and Their Binding of Fullerenes

The synthesis of a new triaminoguanidinium-based ligand with three tris-chelating [NNO]-binding pockets and C₃ symmetry is described. The reaction of tris-(2-pyridinylene-N-oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C₆₀ can be observed by NMR spectroscopy and single-crystal X-ray diffraction and is verified using computation.     

Nitrogen retention in the Szczecin Lagoon,Baltic Sea

Nitrogen (N) retention and transformation in the Szczecin Lagoon, southern Baltic Sea, were studied by means of budget calculations and stable isotope data of dissolved and particulate matter. Two stations, one located at the main outlet of the lagoon (?wina Strait) and the other 100 km to the south, on the Oder River (Widuchowa), were sampled biweekly over the years 2000–2002. The Oder River is one of the five largest rivers draining into the Baltic Sea and the largest one discharging its waters into the western Baltic. According to our data, the Oder River carried approximately 60 kt y^?1 total N, of which 7 kt y^?1 (<12 %) are particulate organic nitrogen and 46 kt y^?1 (77 %) dissolved inorganic nitrogen. Seasonal patterns of particulate nitrogen and nitrate concentrations were similar at Widuchowa and ?wina Strait station, but nitrate concentrations in the ?wina Strait were much lower, pointing not only to the dilution effect but also to considerable nutrient removal capacity (especially of nitrate) in the lagoon. The loss of nitrate suggests that denitrification is the major N-removal process, whereas primary production was only a minor contributor, due to the very low particle load. Combining budget calculations with stable isotope measurements reveal unique information about nitrogen turnover processes in the lagoon.     

Empty pseudo-triangles in point sets

We study empty pseudo-triangles in a set P of n points in the plane, where an empty pseudo-triangle has its vertices at the points of P, and no points of P lie inside. We give bounds on the minimum and maximum number of empty pseudo-triangles. If P lies inside a triangle whose corners must be the convex vertices of the pseudo-triangle, then there can be between Θ(n²) and Θ(n³) empty pseudo-triangles. If the convex vertices of the pseudo-triangle are also chosen from P, this number lies between Θ(n³) and Θ(n⁶). If we count only star-shaped pseudo-triangles, the bounds are Θ(n²) and Θ(n⁵). We also study optimization problems: minimizing or maximizing the perimeter or the area over all empty pseudo-triangles defined by P. If P lies inside a triangle whose corners must be used, we can solve these problems in O(n³) time. In the general case, the running times are O(n⁶) for the maximization problems and O(nlogn) for the minimization problems.     

Coordination chemistry of corroles with focus on main group elements

The discovery of facile methodologies for the synthesis of triarylcorroles initiated extensive research on the corresponding metal complexes, ranging from elucidation of their fundamental physical properties to utilization of their chemical reactivity for many applications. This review focuses on the coordination chemistry of main group elements chelated by tetradentate and trianionic 5,10,15-triarylcorroles, which led to the elucidation of unique photophysical, crystallographic and electrochemical characteristics of these complexes. The facile access to a variety of complexes in which these and other properties can be relatively easily tuned allows for the introduction of metallocorroles as key components in advanced systems, such as for photovoltaic cells and imaging procedures in living organism.     

Highly Selective Barbier‐Type Propargylations and Allenylations Catalyzed by Titanocene(III)

The alkyne functional group is found in many bioactive natural products and is the key to many important chemical transformations developed over recent years. Moreover, allenes have recently gained relevance as versatile reagents in organic synthesis. Mild, catalytic methods to enable the selective introduction of either alkyne or allene motifs into organic molecules are very valuable but, as yet, quite scarce. We describe an extremely mild and selective method for either the propargylation or allenylation of carbonyl compounds catalyzed by the abundant, safe, and inexpensive metal titanium. These reactions can selectively provide homopropargylic alcohols from aldehydes and ketones or α‐hydroxy‐allenes from aldehydes. The mechanisms involved were also investigated.     

Opening the ‘black box’ of simulations: increased transparency and effective communication through the systematic design of experiments

Many still view simulation models as a black box. This paper argues that perceptions could change if the systematic design of experiments (DOE) for simulation research was fully realized. DOE can increase (1) the transparency of simulation model behavior and (2) the effectiveness of reporting simulation results. Based on DOE principles, we develop a systematic procedure to guide the analysis of simulation models as well as concrete templates for sharing the results. A simulation model investigating the performance of learning algorithms in an economic mechanism design context illustrates our suggestions. Overall, the proposed systematic procedure for applying DOE principles complements current initiatives for a more standardized simulation research process.     

3‐Oxa‐6,8‐diaza‐1,2:4,5‐dibenzocycloocta‐1,4‐dien‐7‐one: a three‐dimensional network assembled by hydrogen‐bonding, π–π and edge‐to‐face interactions

The title compound, C₁₃H₁₀N₂O₂, is the first structure in which the urea moiety is incorporated into an eight‐membered ring. Two mol­ecules are found in the asymmetric unit, which are almost identical in their conformation and their hydrogen‐bond pattern. The carbonyl O atom acts as a double acceptor for the NH groups of two adjacent mol­ecules. In this way, infinite tapes are formed, which are connected viaπ–π and edge‐to‐face interactions in the second and third dimension. This hierarchical order of interactions is confirmed by molecular mechanics calculations. Force‐field and semi‐empirical calculations for a single mol­ecule did not find the envelope conformation present in the crystal, indicating instead a C_s conformation. Only with a model consisting of a hydrogen‐bonded dimer or a larger hydrogen‐bonded section was a conformation found that was similar to the one present in the crystal.     

LSn(OCH2CH2)2NR (L = lone pair,W(CO)5; R = Me,t‐Bu). The Molecular Structures of 5‐Aza‐2,8‐dioxa‐1‐stannabicyclo[3.3.0]1.5octanes and Their Tungstenpentacarbonyl Complexes

Single crystal X‐ray diffraction analyses of LSn(OCH₂CH₂)₂NR [ 1 , R = Me, L = lone pair; 2 , R = Me, L = W(CO)₅; 3 , R = t‐Bu, L = W(CO)₅] reveal these compounds to be dimeric and cis‐configurated. The dimerization is realized by intramolecular O→Sn interactions to give four‐membered Sn₂O₂‐rings. In addition, there are intramolecular N→Sn interactions ranging in between 2.356(5) ( 2 ) and 2.549(4) Å ( 3 ).     

Cation‐Controlled Formation and Interconversion of the fac/fac and mer/mer Stereoisomers of a Triple‐Stranded Helicate

Two biscatecholester ligands with oligoether spacers were used to prepare dinuclear titanium(IV) triscatecholate based helicates. In the case of Li₄[( 1 / 2 )₃Ti₂], “classical” helicates with three internally bound Li⁺ ions and syn‐oriented ligands in the complex units (fac/fac isomer) were obtained. In the case of the sodium salt Na₄[( 2 )₃Ti₂], a different homochiral dinuclear triple‐stranded helicate with two internally bound Na⁺ ions was formed. The complex units are anti‐configured, and two of the ligand spacers are connecting internal with external positions of the helicate (mer/mer isomer). Removal of the sodium ions and addition of lithium ions leads to the switching from one topology to the other with an expanded helicate [( 2 )₃Ti₂]^4? as an intermediate. Switching back to the “non‐classical” helicate cannot be observed because severe structural rearrangements would be required.     

Disproportionation Equilibrium of a μ‐Oxodiiron(III) Complex Giving Rise to C−H Activation Reactivity: Structural Snapshot of a Unique Oxoiron(IV) Adduct

μ‐Oxodiiron(III) species are air‐stable and unreactive products of autoxidation processes of monomeric heme and non‐heme iron(II) complexes. Now, the organometallic [(L^NHC)Fe^III‐(μ‐O)‐Fe^III(L^NHC)]⁴⁺ complex 1 (L^NHC is a macrocyclic tetracarbene) is shown to be reactive in C?H activation without addition of further oxidants. Studying the oxidation of dihydroanthracene, it was found that 1 thermally disproportionates in MeCN solution into its oxoiron(IV) ( 2 ) and iron(II) components; the former is the active species in the observed oxidation processes. Possible cleavage scenarios for 1 are shown by scrambling experiments and structural characterization of an unprecedented adduct of 1 and oxoiron(IV) complex 2 . Kinetic analysis gave an equilibrium constant for the disproportionation of 1 , which is very small (K_eq=7.5±2.5×10^?8 m ). Increasing K_eq might by a useful strategy for circumventing the formation of dead‐end μ‐oxodiiron(III) products during Fe‐based homogeneous oxidation catalysis.