Metal organic frameworks showing hydrocarbon adsorption properties commensurate with their pore structure

Commensurate adsorption occurs when the number of molecules adsorbed per unit cell relates to the symmetry of the framework and its topology. While rare in zeolite materials, commensurate adsorption has been observed in several MOF materials. In some MOF materials, several molecules having dimensions within a limited size range show this effect. This paper describes the commensurate adsorption properties of three MOF materials and also two MOFs showing unusual combined structure-composition adsorption features.     

Generalized symmetric planes

In this paper we relate the theory of stable planes to the theory of generalized symmetric spaces in the sense of differential geometry where the symmetries may be of arbitrary order. This leads to the notion of a generalized symmetric plane. We assign to every generalized symmetric plane an associated infinitesimal model and show that the associated infinitesimal model essentially determines a generalized symmetric plane up to global isomorphism. In particular, every generalized symmetric plane with an abelian group of transvections is a topological translation plane.     

Small-dimensional linear programming and convex hulls made easy

We present two randomized algorithms. One solves linear programs involvingm constraints ind variables in expected timeO(m). The other constructs convex hulls ofn points in ℝ ^d ,d>3, in expected timeO(n ^[d/2]). In both boundsd is considered to be a constant. In the linear programming algorithm the dependence of the time bound ond is of the formd!. The main virtue of our results lies in the utter simplicity of the algorithms as well as their analyses. Large portions of the research reported here were conducted while the author visited DIMACS at Princeton University. The author was supported by NSF Presidential Young Investigator Award CCR-9058440.     

Interaction of He Atoms with XeF2 Observed in Crossed Molecular Beams

The interactional shape of XeF₂ with respect to energy and distance was observed by He atom scattering in molecular beam experiments. The heterogeneous second virial coefficient and the binary coefficient of diffusion were calculated from the resulting interaction potential.     

Shell effects in the evolution of the mass asymmetry in heavy-ion collisions leading to composite systems withZ=108

Fragment mass distributions are presented obtained in the heavy-ion reactions²²Ne+²⁴⁹Cf,³²S+²³⁸U,⁴⁰Ar+²³²Th and⁵⁶Fe+²⁰⁸Pb leading to composite systems with equal nuclear charge numberZ=108. The experiments were performed at the heavy-ion cyclotron U 300 of the Laboratory of Nuclear Reactions in Dubna. The spectrometer DEMAS was used to measure the time-of-flight values and the laboratory angles of the correlated fragments. The shape of the mass distributions strongly depends on the initial mass asymmetry. When decreasing the bombarding energy down to values near the Coulomb barrier, the mass distributions obtained in the reactions³²S+²³⁸U and⁴⁰Ar+²³²Th exhibit relative maxima ofM≈205 interpreted to be due to stabilizing effects of nuclear shells during the fragmentation process.     

The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4

The gallides SrRh₂Ga₂, SrIr₂Ga₂, and Sr₃Rh₄Ga₄ were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh₂B₂ type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR₂ = 0.0218, 398 F² values, 15 variables for SrRh₂Ga₂; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr₂Ga₂, and Na₃Pt₄Ge₄ type, I$\bar{4}$ 3m, a = 777.4(2) pm, wR₂ = 0.0234, 190 F² values, 11 variables for Sr₃Ir₄Ga₄. The gallides SrRh₂Ga₂ and Sr₃Ir₄Ga₄ exhibit complex, covalently bonded three‐dimensional [Rh₂Ga₂] and [Ir₄Ga₄] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh₂Ga₂ and by 4 Ir + 8 Ga in Sr₃Ir₄Ga₄. The structure of SrRh₂Ga₂ is discussed along with the monoclinic distortion variants HoNi₂B₂ and BaPt₂Ga₂ on the basis of a group‐subgroup scheme.     

Numerische Simulation der Freispiegelströmung in einem Wasserrad

Es wird ein Berechnungsmodell für 2-Fluid-Strömungen mit drehendem Starrkörper vorgestellt, mit dem eine numerische Analyse der Strömungsvorgänge innerhalb von Schaufelwasserrädern möglich ist. Mit dem vorgestellten Berechnungsmodell erfolgt die erstmalige numerische Untersuchung der bei Schaufelwasserrädern auftretenden Strömungsvorgänge. Dabei werden die wesentlichen Punkte im Rahmen der numerischen Umsetzung eingehend diskutiert und die gewonnenen Ergebnisse anhand experimenteller Daten auf ihre physikalische Plausibilität hin überprüft. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural Diversity of Metallosupramolecular Assemblies from Cu(phen)2+ (phen = 1,10‐Phenanthroline) Building Blocks and 4,4′‐Bipyridine

Attempts to crystal engineer metallosupramolecularcomplexes from Cu(phen)²⁺ building blocks and the prototypical,rod‐like, exo‐bidentate ligand 4,4′‐bipyridine (4,4′‐bipy) by layering techniques are described. Reactions of Cu(phen)²⁺ (phen = 1,10‐phenanthroline) with 4,4′‐bipy in the presence of NO₃^– counterions yielded two distinct, discrete, dinuclear, C_i symmetric, dumbbell‐typecomplexes, [{Cu(NO₃)₂(phen)}₂(4,4′‐bipy)] ( 1 ) and [{Cu(NO₃)(phen)(H₂O)}₂(4,4′‐bipy)](NO₃)₂ ( 2 ), depending upon the mixture of solvents used for crystallization. In compound 1 , a mono‐ and a bidentate nitrato group coordinate to Cu²⁺, whereas in 2 the monodentate nitrato groups are replaced by aqua ligands, which introduce additional hydrogen‐bond donor functionality to the molecule. The crystal structure of 1 was determined by single‐crystal X‐ray analysis at 296 and 110 K. Upon cooling, a disorder‐order transition occurs, with retention of the space group symmetry. The crystal structure of 2 at room temperature was reported previously [Z.‐X. Du, J.‐X. Li, Acta Cryst. 2007 , E63, m2282]. We have redetermined the crystal structure of 2 at 100 K. A phase transition is not observed for 2 , but the low temperature single‐crystal structure determination is of significantly higher precision than the room temperature study. Both 1 and 2 are obtained phase‐pure, as proven by powder X‐ray diffraction of the bulk materials. Crystals of [Cu(phen)(CF₃SO₃)₂(4,4′‐bipy) · 0.5H₂O]_n ( 3 ), a one‐dimensional coordination polymer, were obtained from [Cu(CF₃SO₃)₂(phen)(H₂O)₂] and 4,4′‐bipy. In 3 , Cu(phen)²⁺ corner units are joined by 4,4′‐bipy via the two vacant cis sites to form polymeric zig‐zag chains, which are tightly packed in the crystal. Compounds 1 – 3 were further studied by infrared spectroscopy.