نتایج جستجو برای: transition metal cation
تعداد نتایج: 485699 فیلتر نتایج به سال:
Transition metal ions in aqueous solutions generally exist as complex ions in which water molecules, acting as Lewis bases, "coordinate" or bond with the small cation (which acts as a Lewis acid). The water molecules in these structures are known as ligands. Historically this kind of attachment has been called either a coordinate covalent bond or a dative bond. The distinguishing characteristic...
-The conditions under which an exchanger phase will behave as an ideal mixture are established from thermodynamic principles. It is shown that, if a stoichiometric cation-exchange reaction is reversible, the exchanger phase will exhibit ideal behavior if the Vanselow selectivity coefficient is independent of the exchanger composition. This criterion is applied to some recently published data fo...
The novel pentaborate with a transition-metal complex as counter-cation and with water of crystallization, tris(ethylenediamine)cobalt(II) bis[4,4',6,6'-tetrahydroxy-2,2'-spirobi(cyclotriboroxane)(1-)] dihydrate, [Co(C(2)H(8)N(2))(3)][B(5)O(6)(OH)(4)](2)·2H(2)O, forms a three-dimensional supra-molecular framework through O-H⋯O hydrogen bonding among the [B(5)O(6)(OH)(4)](-) anions with large ch...
We report a Lewis acid catalyzed reaction sequence involving a 1,2-shift and subsequent C–H insertion that gives monocyclic and fused bicyclic cyclopentenone products. This reaction sequence, which is initiated by treating b-hydroxy-a-diazo ketones with a Lewis acid, proceeds through vinyl cation intermediates that insert at non-activated gamma C–H bonds. This reaction represents an alternative...
Luminescent zeolites exchanged with two distinct and interacted emissive ions are vital but less-studied for the potential applications in white light emitting diodes, solar cells, optical codes, biomedicine and so on. Typical transition metal ion Mn2+ and lanthanide ion Yb3+ are adopted as a case study via their characteristic transitions and the interaction between them. The option is conside...
This study probes the magnetic and ferroelectric ordering of the NH4M(HCO2)3 (M = Mn(2+), Fe(2+), Co(2+) and Ni(2+)) frameworks using neutron diffraction, improving the understanding of the origins of the properties of these fascinating multiferroics. This rare study of the magnetic structure of a family of metal-organic frameworks shows that all four compounds exhibit antiferromagnetic couplin...
Metal–dithiolene complexes form very attractive categories of molecular metals and superconductors. They can have various oxidation states and can range from electron acceptors to donors. The first observation of metallic behavior in crystalline metal– dithiolene complexes was reported for Li0.75[Pt(mnt)2]?2H2O [mnt~maleonitriledithiolate; Scheme 1] by Underhill et al. in 1981. The conduction p...
The role of alkali metal cations in the stabilization of guanine quadruplexes: why K(+) is the best.
The alkali metal ion affinity of guanine quadruplexes has been studied using dispersion-corrected density functional theory (DFT-D). We have done computational investigations in aqueous solution that mimics artificial supramolecular conditions where guanine bases assemble into stacked quartets as well as biological environments in which telomeric quadruplexes are formed. In both cases, an alkal...
In this study we present x-ray diffraction data on metal phosphates containing either high or low coordination number zinc or calcium. The experiments reveal that low-coordination zinc phosphate crystals are relatively soft at ambient conditions but stiffen dramatically with pressure, p, thereby exhibiting smart materials behavior. In comparison, high-coordination zinc and calcium phosphates ha...
An object-oriented approach to the analysis and design of metal forming and directional solidi cation processes is presented. A number of speci c ideas are introduced on how a deformation or a solidi cation process can be partitioned into subproblems that can be independently developed and tested in the form of class hierarchies. Class development based on mathematical and/or physical arguments...
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