Complete encapsulation

Fig. 19.9 Methods of mounting specimens, (a) Wire soldered to metal specimen, wire being enclosed in glass tube (b) specimen completely encapsulated in cold-setting resin and resin ground down to expose one face (c) specimen clipped into machined p.t.f.e. holder (d) Stern-Makrides pressure gasket for cylindrical specimen (e) pressure gasket for sheet or foil ...

It should be noted that the three-dimensional polyether cages (the cryptands) are usually most effective at producing naked anions . With these, the metal ion is completely encapsulated by the polyether network and thus better charge separation is achieved. In the case of the crowns, such complete encapsulation does not normally occur and hence the counter anion is more readily able to associate directly with the com-plexed metal cation. In such cases, the use of the term naked is somewhat of a misnomer. 

In the dianion [Fe6(CO)i6C]2-, the carbide atom is completely encapsulated in the octahedral metal cage. This dianion (86 valence electrons) does not exhibit any redox process with characteristics of chemical reversibility.ld... 

A completely different arrangement of the six metal atoms is present in the phosphide monoanion [Os6(CO)i8P]. In fact, Figure 49 shows that the phosphorus atom is completely encapsulated in a trigonal-prismatic metal cage. 

Two-phase domain morphology, of approximately spherical shape, comprising two polymers, each in separate phase domains, in which phase domains of one polymer completely encapsulate the phase domains of the other polymer. 

Multiphase morphology in which dispersed phase domains of one polymer contain and completely encapsulate many phase domains of a second polymer that may have the same composition as the continuous phase domain. 

We started this templated approach to catalyst encapsulation using tris(mefa-pyridyl)phosphine and zinc(ii)TPP (TPP = tetraphenylporphyrin) [7]. From NMR and UV/Vis titration experiments we found a selective assembly process via coordination of the nitrogen to the zinc(ii)TPP, rendering the phosphine donor atom completely encapsulated by the three porphyrin components (Figure 8.4). The phosphine center is still available for coordination to transition metals, providing... 

Figure 8.3 Templated approach to ligand encapsulation. Molecular modeling demonstrates that the phosphine ligand is completely encapsulated (see also Figure 8.4).

A monophosphine complex is formed when 3 is mixed with three equivalents of a zinc(ii)salphen complex and half an equivalent of Rh(acac)(CO)2 (acac = acetyl acetonate), whereas the assembly based on template 4 and the zinc(n)salphen complexes forms a bis-phosphine rhodium species. In the latter case, the bisphosphine rhodium complex is completely encapsulated by six salphen building blocks. This difference in mono- versus diphosphine ligation to the Rh -center and, to a lesser extent, the difference in electronic features (and thus donating properties of the phosphine) between template ligands 3 and 4, can be used to induce a different catalytic behavior. 

In the 1 1 NaBF4 complex of (111) the cation is completely encapsulated by the tricyclic ligand and bound to all eight donor atoms.3911 In the structure of the dipotassium complex of... 

X-ray structure of the mesitylene derivative was reported shortly afterward.11 This represented the second structurally characterized cluster containing an interstitial atom [the structure of FesC(CO)i5 having already been established]12 and the first example of a cluster with a completely encapsulated carbide atom. At the time that the synthesis of 2 was first reported, another paper described the synthesis of a cluster also obtained from 3 when heated to 150°C in either benzene or cyclohexane. Based on an estimation of the mass of this compound from a differential vapor pressure measurement, the authors suggested that this compound corresponded to Ru6(CO)18.13 It was subsequently noted from a comparison of vco IR data and a structural determination that this compound was in fact 2. 

The carbide atom in 1 is located in the center of the square face such that it is partially exposed whereas the carbide atom in 2 is completely encapsulated by the six ruthenium atoms. From a spectroscopic viewpoint, carbide atoms are very distinctive and the earlier reviews have dealt with these aspects in detail.7 8 The IR spectrum of 1 contains peaks at 701 (s) and 670(m) cm 1, and 2 contains peaks at 717(sh), 703(s), 680(m), and 669(m) cm-1.22 I3C-NMR spectra of 1 and 2 do not appear to have been reported. This is probably due to the low yields in which these compounds were initially obtained at a time when, 3C-NMR was still not in widespread use in cluster chemistry. In general, the 13C-NMR resonance of carbide atoms ranges from 8 250 to 500. The high frequency resonances exhibited in 13C-NMR spectra reflect the different diamagnetic and paramagnetic effects experienced by a nucleus in such an unusual chemical environment.23... 

The X-ray structure of the L-Sr(Picrate)2 (L = p-tert-butyl-calix[4]arene-tetra(diethylamide)) is reported, as well as MD simulations on the L M2+ complexes in vacuo, in water, and in acetonitrile solutions for alkaline earth cations with a comparison of converging and diverging conformers.130 In the simulated and solid-state structures of the L M2+ complex, the ligand wraps around the complexed cations M2+ (more than it does with alkaline cations), which are completely encapsulated within the polar pseudo-cavity of L, without coordination to its counterion in the crystal or to solvent molecules in solution. In contrast to alkali cation complexes, which display conformational flexibility in solution, computations show that the alkaline earth cation complexes are of the converging type in water and in acetonitrile. Subtle structural changes from Mg2+ to Ba2+ are observed in the gas phase and in solution. Based on FBP calculations, a binding sequence of alkaline earth cations was determined Mg2+ displays the weakest affinity for L, while Ca2+ and Sr2+ are the most stable complexes, which is in agreement with the experiment. 

An example of this design was recently reported by Atwood and coworkers, who showed that an extended, deep-cavity resorcinarene derivative can completely encapsulate a NMe4+ cation with a Cl" anion positioned by hydrogen bonding at the capsule entrance (see schematic receptor 12). [20]... 

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

The first one is a hydrogenation autoclave for 250 bars and 350 °C with a completely encapsulated agitator, the second one a vessel for tobacco expansion with nitrogen, designed for a minimum of 140,000 cycles at 825 bars and 100 °C. 

The sealing of a rotating shaft under low leakage conditions is extremely difficult, therefore the stirrer shaft was built completely encapsulated by austenitic material and the transmission of the torque was realised using a permanent magnetic coupling. The magnets were based on samarium-cobalt and are able to transmit a torque of 135 Nm. 

Several clusters are known in which the C2 ligand lies more-or-less exposed on the surface of an M cluster or within a cavity, but not completely encapsulated by the metal core. A theoretical study of these... 

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