Square capped

Fig. 22 a Skeletal representations of the four closed tetramers with alkyl substituents removed b space-filling models of the isopropyl-derived cube and the more open square-capped macrocycle both homochiral and obtained from DFT calculations... 

H - H interactions, both for all-(S) and (R,R,S,S) tetramers, even after conformational energy minimisation. Overall, most of the >40 kcal mol-1 enthalpic advantage of the [dimer + dimer to tetramer] process is lost on going from methylzinc to isopropylzinc-derived structures, because of the increased steric strain. The remaining [Zn-Oh square-based tetramers are all more strained in the isopropyl than in the Me series. As an extreme, the latter is less stable than two isolated monomers. What stands out is that the square-capped macrocycle is only modestly more strained in the isopropyl series, and lacks severe H - H interactions (only two H - H contacts are below 2.3 A). Forming the barrel isomer from this by making two additional Zn - N... 

Xc02F2 CsXeOFj KXeOjF 30.8 C21, see-saw Distorted octahedral Square pyramidal (chain) Trigonal bipyramidal (1) Capped octahedral (1) Octahedral (1)... 

MFg] , capped trigonal prismatic [MFv], and even square-antiprismatic [MFg] salts can all be isolated. By contrast with the fluorides, aqueous solutions of MCI5 and MBrs (M = Mb, Ta) yield only oxochloro- and oxobromo-complexes, though the application of non-aqueous procedures allows their use as starting materials. 

Key Colour % indicates preparation but no report of colour) mp/°C (na indicates value not reported) coordination 9 ttp = tricapped trigonal prismatic 8 d = dodecahedral 8 sa = square antiprismatic 8 btp = bicapped trigonal prismatic 8,7 = mixed 8- and 7-coordination (SrBr2 structure) 7 cc = capped octahedral 7 pbp = pentagonal bipyramidal 6 o = octahedral 6 och = octahedral chain, 6 ol = octahedral layered. 

Example 11.8 With highly reactive absorbents, the mass transfer resistance in the gas phase can be controlling. Determine the number of trays needed to reduce the CO2 concentration in a methane stream from 5% to 100 ppm (by volume), assuming the liquid mass transfer and reaction steps are fast. A 0.9-m diameter column is to be operated at 8 atm and 50°C with a gas feed rate of 0.2m /s. The trays are bubble caps operated with a 0.1-m liquid level. Literature correlations suggest = 0.002 m/s and A, = 20m per square meter of tray area. 

Replacing any of the fluorine atoms of SFg gives a molecule with a square of fluorine ligands capped by... 

Figure 3. A comparison of the aC backbone of PelC with PelE. The aCs which superimpose within a root-mean-square deviation of 1.5 A are shown in black and those, within 3.0 A are shown in dark gray. The remaining backbone regions are shown in light The largest structural differences occur in the loops capping one end of the parallel p as well as in those comprising the putative substrate binding groove.

Electrochemical experiments have been carried out on materials deposited by PVD on silicon microfabricated arrays of Au pad electrodes [Guerin et al., 2006a]. The substrate is made up of a square silicon wafer capped with silicon nitride (31.8 mm x 31.8 mm), which has an array of 100 individually addressable Au pad electrodes. These electrodes make up a square matrix on the wafer, which can be masked when placed in a PVD chamber, allowing deposition of thin films on the Au electrodes. Figure 16.3 is a schematic drawing of the configuration. Small electrical contact pads in Au for the individual addressing of electrodes (0.8 mm x 0.8 mm) are placed on the boundaries. 

Possible stereochemistries for eight-coordinate [Ln(H20)8]3+ are the dodecahedron, the square antiprism, and the cube, although the last seems less likely (295). The proposed nine-coordinate [Ln(H20)9]3+ tri-capped trigonal prism transition state is similar to the [Ln(H20)9]3+ structures observed in the solid state. Thus, the possible water exchange... 

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