Search results for "Sem"
showing 10 items of 8949 documents
Supramolecular Architectures Based on Phosphonic Acid Diesters
2014
The interest of phosphonic acid dialkyl esters for generation of metal-organic materials is discussed using derivatives of porphyrin and 1,10-phenanthroline series as representative examples.
Self‐Assembly and Characterisation of Grid‐Type Iron( II ), Cobalt( II ) and Zinc( II ) Complexes
2003
The reaction of the ligands 5 and 6, containing two tridentate binding units, with iron(II), cobalt(II) and zinc(II) leads to the self-assembly of supramolecular architectures of [2 × 2] grid type containing four ions in octahedral coordination sites. The grid-type structures have been assigned on the basis of the spectroscopic data in solution, and confirmed in the solid state in the case of complexes 6b and 6c by X-ray crystallography. The latter study revealed that each metal ion is situated in a distorted octahedral coordination environment comprising two N,N,O ligand donor sets. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Magnetostructural correlations in CuII−NC−WV linkage: the case of [CuII(diimine)]2+−[WV(CN)8]3− 0D assemblies
2009
International audience; We report on the syntheses, crystal structures, and magnetic properties of two cyano-bridged molecular assemblies: [CuII(phen)3]2{[CuII(phen)2]2[WV(CN)8]2}(ClO4)2·10H2O (phen = 1,10-phenanthroline) (1) and {[CuII(bpy)2]2[WV(CN)8]} {[CuII(bpy)2][WV(CN)8]}·4H2O (bpy = 2,2′-bipyridyl) (2). Compound 1 consists of cyano-bridged [CuII2WV2]2− molecular rectangles and isolated [CuII(phen)3]2+ complexes. The molecular structure of 2 reveals cyano-bridged trinuclear [CuII2WV]+ and dinuclear [CuIIWV]− ions. Magnetic interactions in 1 are interpreted in terms of the model of a tetranuclear moiety consisting of two ferromagnetic CuII−NC−WV units (J1 = +39(4) cm−1) interacting ant…
Supramolecular Assembly of Organophosphonate Diesters Using Paddle-Wheel Complexes: First Examples in Porphyrin Series
2014
The reactions of dicopper tetrapivalate complex Cu2(μ-OOC-t-Bu)4(NCMe)2 (1) with triphenylphosphine oxide and diethyl phosphite allow paddle-wheel (PW) copper(II) complexes with phosphorus-containing axial ligands (2, 3) to be obtained. When meso-bis(diethoxyphosphoryl)porphyrins 4M were employed in this ligand exchange reaction, a series of one-dimensional (1D) homo- and heterometallic coordination polymers 5M composed of PW subunits and organophosphonate diesters were prepared and characterized by means of single crystal X-ray analysis. Planar porphyrinate 4Pd and nonplanar metalloporphyrinates 4Cu and 4Ni proved to be appropriate molecular structural blocks for assembly of coordination p…
Controlling the Host-Guest Interaction Mode through a Redox Stimulus
2017
International audience; A proof-of-concept related to the redox-control of the binding/releasing process in a host-guest system is achieved by designing a neutral and robust Pt-based redox-active metallacage involving two extended-tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host-guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host-guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental d…
Reactions in the presence of irradiated semiconductors: Are they simply photocatalytic?
2018
A generally accepted classification distinguishes semiconductor photocatalysis in type A and type B. The first class comprehends reactions where the primary redox products (radical anions and cations) further evolve giving rise to the final reduced and oxidized species. Type B reactions occur when the primary redox products undergo intermolecular bond formation to addition products. Recently, some photocatalytic reactions have been reported wherein the photocatalytically produced compounds are not the final products. In fact, they react in the solution bulk or catalytically on the surface of the semiconductor with other species thus producing the target compounds. These reactions, hereby re…
Pre- and syn-eruptive geochemistry of volcanic gases from Soufriere Hills of Montserrat, West Indies
1998
International audience; Soufriere Hills fumaroles contained magmaderived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal coinposition. Chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at Galway's Soufriere, the most active fumarolic field. Hydrothermal buffering of the fumaroles has been favoured by their remote location (!-2 km) froin the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater. High temperature (720øC) gas collected froin the extruding lava dome in Feb. 1996 was chemically and isotopically repres…
Tectono-metamorphic evolution of the internal zone of the Pan-African Lufilian orogenic belt (Zambia): Implications for crustal reworking and syn-oro…
2016
Abstract The internal zone of the Pan-African Lufilian orogenic belt (Zambia) hosts a dozen uranium occurrences mostly located within kyanite micaschists in a shear zone marking the contact between metasedimentary rocks attributed to the Katanga Neoproterozoic sedimentary sequence and migmatites coring domes developed dominantly at the expense of the pre-Neoproterozoic basement. The P–T–t–d paths reconstructed for these rocks combining field observations, microstructural analysis, metamorphic petrology and thermobarometry and geochronology indicate that they have recorded burial and exhumation during the Pan-African orogeny. Both units of the Katanga metasedimentary sequence and pre-Katanga…
Whole-rock Nd–Hf isotopic study of I-type and peraluminous granitic rocks from the Chinese Altai: Constraints on the nature of the lower crust and te…
2017
Abstract The nature of the lower crust and tectonic setting of the Chinese Altai in the early to middle Paleozoic are still hotly debated. Decoupling between zircon Hf and whole-rock Nd isotopic systems for granites results in different interpretations for the above issues. In order to solve the problem, whole-rock Nd–Hf isotopic analyses were conducted on representative early to middle Paleozoic I-type granite and strongly peraluminous granites and rhyolites from the Chinese Altai. The I-type granites show metaluminous to weakly peraluminous feature and have eNd(t) values ranging from − 2.2 to + 0.8 and eHf(t) from + 3.9 to + 12.9, respectively. The strongly peraluminous granites and rhyol…
Using hydrological connectivity to detect transitions and degradation thresholds: Applications to dryland systems
2020
In arid and semi-arid ecosystems, shortage of water can trigger changes in landscapes’ structures and function leading to degradation and desertification. Hydrological connectivity is a useful framework for understanding water redistribution and scaling issues associated with runoff and sediment production, since human and/or natural disturbances alter surface water availability and pathways increasing/decreasing connectivity. In this paper, we illustrate the use of the connectivity framework for several examples of dryland systems that are analysed at a variety of spatial and temporal scales. In doing so, we draw particular attention to the analysis of coevolution of system structures and …