Syntheses,structural analyses,and magneto-structural correlations of three polymeric Fe(II) complexes with azide ligand

Three new metal-organic polymeric complexes, [Fe(N(3))(2)(bpp)(2)] (1), [Fe(N(3))(2)(bpe)] (2), and [Fe(N(3))(2)(phen)] (3) [bpp = (1,3-bis(4-pyridyl)-propane), bpe = (1,2-bis(4-pyridyl)-ethane), phen = 1,10-phenanthroline], have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature magnetic measurements in the range 300-2 K. Complexes 1 and 2 crystallize in the monoclinic system, space group C2/c, with the following cell parameters: a = 19.355(4) A, b = 7.076(2) A, c = 22.549(4) A, beta = 119.50(3) degrees, Z = 4, and a = 10.007(14) A, b = 13.789(18) A, c = 10.377(14) A, beta = 103.50(1) degrees, Z = 4, respectively. Complex 3 crystallizes in the triclinic system, space group P(-)1, with a = 7.155(12) A, b = 10.066(14) A, c = 10.508(14) A, alpha = 109.57(1) degrees, beta = 104.57(1) degrees, gamma = 105.10(1) degrees, and Z = 2. All coordination polymers exhibit octahedral Fe(II) nodes. The structural determination of 1 reveals a parallel interpenetrated structure of 2D layers of (4,4) topology, formed by Fe(II) nodes linked through bpp ligands, while mono-coordinated azide anions are pendant from the corrugated sheet. Complex 2 has a 2D arrangement constructed through 1D double end-to-end azide bridged iron(II) chains interconnected through bpe ligands. Complex 3 shows a polymeric arrangement where the metal ions are interlinked through pairs of end-on and end-to-end azide ligands exhibiting a zigzag arrangement of metals (Fe-Fe-Fe angle of 111.18 degrees) and an intermetallic separation of 3.347 A (through the EO azide) and of 5.229 A (EE azide). Variable-temperature magnetic susceptibility data suggest that there is no magnetic interaction between the metal centers in 1, whereas in 2 there is an antiferromagnetic interaction through the end-to-end azide bridge. Complex 3 shows ferro- as well as anti-ferromagnetic interactions between the metal centers generated through the alternating end-on and end-to-end azide bridges. Complex 1 has been modeled using the D parameter (considering distorted octahedral Fe(II) geometry and with any possible J value equal to zero) and complex 2 has been modeled as a one-dimensional system with classical and/or quantum spin where we have used two possible full diagonalization processes: without and with the D parameter, considering the important distortions of the Fe(II) ions. For complex 3, the alternating coupling model impedes a mathematical solution for the modeling as classical spins. With quantum spin, the modeling has been made as in 2.     

Reduced molybenum-oxide-based core-shell hybrids: "blue" electrons are delocalized on the shell

The present study refers to a variety of reduced metal-oxide core-shell hybrids, which are unique with regard to their electronic structure, their geometry, and their formation. They contain spherical {Mo72Fe30} Keplerate-type shells encapsulating Keggin-type polyoxomolybdates based on very weak interactions. Studies on the encapsulation of molybdosilicate as well as on the earlier reported molybdophosphate, coupled with the use of several physical methods for the characterization led to unprecedented results (see title). Upon standing in air at room temperature, acidified aqueous solutions obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid, and molybdosilicic acid led to the precipitation of monoclinic greenish crystals (1). A rhombohedral variant (2) has also been observed. Upon drying at room temperature, compound 3 with a layer structure was obtained from 1 in a solid-state reaction based on cross-linking of the shells. The compounds 1, 2, and 3 have been characterized by a combination of methods including single-crystal X-ray crystallography, magnetic studies, as well as IR, M?ssbauer, (resonance) Raman, and electronic absorption spectroscopy. In connection with detailed studies of the guest-free two-electron-reduced {Mo72Fe30}-type Keplerate (4) and of the previously reported molybdophosphate-based hybrids (including 31P NMR spectroscopy results), it is unambiguously proved that 1, 2, and 3 contain non-reduced Keggin ion cores and reduced {Mo72Fe30}-type shells. The results are discussed in terms of redox considerations (the shell as well as the core can be reduced) including those related to the reduction of "molybdates" by FeII being of interdisciplinary including catalytic interest (the MoVI/MoV and FeIII/FeII couples have very close redox potentials!), while also referring to the special formation of the hybrids based on chemical Darwinism.     

Ultraslow solitons due to large quintic nonlinearity in coupled quantum well structures driven by two control laser beams

In this paper, we have shown the existence of large amounts of quintic nonlinearity in asymmetric three-coupled quantum wells, which arise due to a probe pulse and two controlling laser beams. The possibilities of generation and propagation of ultraslow bright optical solitons in these systems have been examined in situations of both Kerr and quintic nonlinearities. We have also demonstrated numerically that these solitons are stable. The modulation instability of a continuous or quasi-continuous wave probe beam has been also investigated and the role of quintic nonlinearity in suppressing this instability has been addressed.     

Montmorillonite Supported Borohydride: A New Reducing Agent for Reductions Under Phase Transfer Conditions

A few cyclic and acyclic ketones were reduced in dichloro-methane, using reducing agents prepared from reusable montmorillonite clay supported phase transfer catalyst. A high percentage of axial attack (76–100%) by hydrides on substituted cyclohexanones observed, has been rationalised on the basis of a four center cyclic transition state for the clay absorbed ketone.     

Neutrino propagation in a weakly magnetized medium

Neutrino-photon processes, forbidden in vacuum, can take place in the presence of a thermal medium and/or an external electro-magnetic field, mediated by the corresponding charged leptons (real or virtual). Such interactions affect the propagation of neutrinos through a magnetized plasma. We investigate the neutrino-photon absorptive processes, at the one-loop level, for massless neutrinos in a weakly magnetized plasma. We find that there is no correction to the absorptive part of the axial-vector-vector amplitude due to the presence of a magnetic field, to the linear order in the field strength.     

Solid-state transformation from self-assembled nanosheets into ordered nanorods

ZnO nanostructures, with a rich collection of morphologies and spatial organizations useful in a variety of important applications, have been synthesized mainly via solution- and gas-phase approaches. Here we report a simple calcination to convert self-assembled nanosheets of hydrated ZnO, each about 50 nm thick, to ordered ZnO nanorods (approximately 200 nm in diameter and approximately 4 microm in length) on glass substrates or on ZnO microcrystals through a quick calcination at 400 degrees C in air. This work is among the first using a pure solid-state transformation to convert one ordered precursory nanostructure to another with different morphology and spatial organization. Both the ordered nanorods and the self-assembled nanosheets could be useful in important applications including catalysis, sensing, gas storage, and drug delivery.     

Mixed-valent dodecanuclear vanadium cluster encapsulating chloride anions and its reaction to form a "bowl"-shaped cluster

Two oxovanadium phosphonate cage compounds have been synthesized in an organic solvent, and their characterization has been done by single-crystal X-ray analysis, IR spectroscopy, and bond valence sum calculations. The simple reaction of a mixed-valent closed V12 cage system produced another quasi-closed system composed of two V6 bowl-type cages.     

Thia- und Dithia-cycloalkane und die Spaltung einiger gesättigter Heterocyclen mit Methyljodid

Zusammenfassung Die 8- und 9-gliedrigen Thia-cycloalkane und die dimeren 14-, 16- und 18-gliedrigen Ringsulfide wurden aus den entsprechenden ,-Dibromalkanen und Natriumsulfid in hochverdünnter alkoholischer Lösung erstmalig dargestellt und charakterisiert. Die Beweisführung für die Struktur der Monomeren erfolgte durch Ringspaltung mit Methyljodid und Identifizierung der entstandenen ,-Dijodalkane.Es wird gezeigt, daß die Ringspaltungsmethode mit Methyljodid unter Herauslösung der gesamten C-Kette auch auf gewisse gesättigte O- und N-Heterocyclen anwendbar ist. Tetrahydrofuran, 1,6-Epoxyhexan und 1,4-Dioxan sowie der Trimethyleniminring werden sämtlich in verschiedenem Ausmaß gespalten, nicht aber die Polymethylenimine mit 4 bis 7 C-Atomen. Im spirocyclischen N,N-Hexamethylen-piperidiniumjodid wird jedoch der 7-gliedrige Ring gesprengt. Piperazin wird nicht angegriffen, wohingegen die Ringhomologen, 1,5-Diaza-cyclooctan und 1,10-Diaza-cyclooctadecan der Spaltung zugänglich sind.Soweit untersucht, werden Benzoyl und p-Toluolsulfonyl am Stickstoff allgemein durch Methyl verdrängt, p-Nitrophenyl und o,p-Dinitrophenyl werden aber nicht ausgetauscht.Mit 4 Abbildungen.