Acetone clusters

Figure 14a shows a portion of the TOF spectrum of the acetone cluster ions in the case where the water content in the acetone sample is 0.4% or less. There are no peaks corresponding to (T)3(H20)+ (mass 192) or (T)3 (H20) H+ (mass 193), and one can readily identify the ion peaks at masses 157 and 215 corresponding to the (T)m 2 C6HII0+ (m > 2) ions as clearly originating from the direct elimination of water molecules from the (T)m H+ via the reaction ... 

Figure 9.2 (a) Example of structuring of water (blue, or light gray Y shaped molecules) and acetone (purple or darker gray) molecules in the shell around a PCL chain (white spheres) constituted by 30 monomers in a equimolar water-acetone mixture instantaneous realization obtained by molecular dynamics simulation, (b) Snapshots of the molecular dynamics simulation of the same PCL chain, visible in white at the center of the simulation box, in an equimolar acetone-water mixture, showing how the polymer shape modifies and the acetone clustering phenomenon of the liquid around the polymer the water is represented in yellow, while acetone is not shown for clarity (courtesy of Nicodemo Di Pasquale). 

Base catalysis is another area which has received a recent stimulus from developments in materials science and microporous solids in particular. The Merk company, for example, has developed a basic catalyst by supporting clusters of cesium oxide in a zeolite matrix [13]. This catalyst system has been developed to manufacture 4-methylthiazole from acetone and methylamine. 

Another approach can be the displacement of the surface Hgands by a reactive gas such as CO, leading to unstable intermediates that will eventually condense into particles. This procedure can be apphed to M(dba)2 (dba = dibenzyhdene acetone M = Pd Pt) [26-28,33,34]. In this case, however, CO remains at the surface of the growing clusters and may modify their chemistry. The reaction conditions (temperature, gas pressure, concentration of precursors and stabilizers) have a strong influence on the nature of the particles formed, primarily on their size. 

The reaction of Cu vapor with acetone and the further clustering at room temperature affords Cu nanostructured powders containing metal particles averaging 3M-nm in diameter (Figure 2). 

In the latter case the dopant is ionised, interacts with the solvent and, subsequently, solvent clusters interact with the analyte. Molecular and protonated molecular ions are observed, indicating that ionisation can occur via proton (toluene) and electron transfer (acetone). 

Figure 14. Reflectron-TOF spectra of acetone (T) cluster ions. Am (T)mH+, Bm (T)mCH5, Cm = (T)mC2H30+. (a) 0.4% water in the acetone sample, (T)i C6HnO+ (mass 157) and (T)2-C6HnO+ (mass 215) are seen, whereas ion signal corresponds to (T)3-H30+ (mass 193 is not found), (b) 0.7% water in the acetone sample, all peaks corresponding to masses 157, 215, and 193 are observed, (c) 1.0% water in the acetone sample, ion peaks corresponding to (T)vC6HnO+ (mass 157) and (T)2 C6HnO+ (mass 215) are not seen however, (T)3-H30+ (mass 193) is clearly identified. Neutral clusters are ionized at 355 nm using a pulsed Nd YAG laser. Taken with permission from ref. 2.

Experiments made at higher degrees of aggregation have provided strong evidence192 for ring-like structures for mixed neutral clusters. For example, under a wide variety of experimental conditions, mixed cluster ions display a maximum intensity atm = 2(n + 1) whenn<5 for (NH3)II (M)mH+, andm = n + 2 whenn<4 for (H20)B(M)mH+ M is a proton acceptor such as acetone, pyridine, and trimethy-lamine. These findings reveal that the cluster ions with these compositions have stable solvation shell structures as discussed above. 

A review of preparative methods for metal sols (colloidal metal particles) suspended in solution is given. The problems involved with the preparation and stabilization of non-aqueous metal colloidal particles are noted. A new method is described for preparing non-aqueous metal sols based on the clustering of solvated metal atoms (from metal vaporization) in cold organic solvents. Gold-acetone colloidal solutions are discussed in detail, especially their preparation, control of particle size (2-9 nm), electrophoresis measurements, electron microscopy, GC-MS, resistivity, and related studies. Particle stabilization involves both electrostatic and steric mechanisms and these are discussed in comparison with aqueous systems. 

The higher catalytic activity of the cluster compound [Pd4(dppm)4(H2)](BPh4)2 [21] (20 in Scheme 4.12) in DMF with respect to less coordinating solvents (e.g., THF, acetone, acetonitrile), combined with a kinetic analysis, led to the mechanism depicted in Scheme 4.12. Initially, 20 dissociates into the less sterically demanding d9-d9 solvento-dimer 21, which is the active catalyst An alkyne molecule then inserts into the Pd-Pd bond to yield 22 and, after migratory insertion into the Pd-H bond, the d9-d9 intermediate 23 forms. Now, H2 can oxidatively add to 23 giving rise to 24 which, upon reductive elimination, results in the formation of the alkene and regenerates 21. 

Mononuclear ruthenium complexes were found to be superior to carbonyl clusters during a comprehensive comparison of a variety of catalysts in the reduction of acetone [49]. Without solvent, most catalysts were highly selective, although the activity was quite low. The addition of water to the system vastly increased yields, in agreement with Schrock and Osborrfs observations into rhodium-catalyzed hydrogenations (Table 15.9) [41],... 

The only new report of a group 7 complex with thallium is the reaction of [Re7C(CO)2i]3 ion with T1PF6 (Equation (92)).94 The thallium adds in a triply bridging fashion opposite to the capping Re(CO)3 unit 99.94 The complex is stable in dichloromethane but dissociates in coordinating solvents. In acetone, infrared data indicated that the complex would be 99% dissociated at concentrations of the cluster of about 10-4M. Addition of halide ions to dichloromethane solutions causes a precipitation of the thallium(i) halide. 

L = PPh3, P(p-MeCgH4)3, or P(p-FC6H4)3]. Of more fundamental interest was i.r. evidence for the formation of the hitherto unknown Rh2(CO)g from the low -temperature (high-pressure) reaction between Rh4(CO)i2 and CO. Whereas Rh (CO)j2 catalyses the hydroformylation of propene in toluene, the use of more polar solvents such as methanol and acetone has been shown to yield instead RhglCO) , and the first reported acyl clusters [NR4][Rhg-(CO)is(COR)] [R = Et(ethylene) or Pr(propene)]. The presence of the acyl group was confirmed from the i.r. spectra (1655—1670 cm ). ... 

Both anionic clusters can be extracted with [(Ph3P)2N]Cl dissolved in acetone but in 65% yield only because they are partially retained by the surface of MgO [3, 15-17]. 

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