Hydroxide complexes clusters

Figure 6.31 The structures of (a) dodeca-, (b) pentadeca-, and (c) octadeca-nuclear clusters templated by two IX4-H ions, a X5-X (X = C1, Br) ion, and Xe p r r r r r COj , respectively. Formal assembly of a 60-metal hydroxide complex featuring 26 vertex-sharing [Ln4(ti3-OH)4] cubane units. These cubane building blocks form six dodecanuclear squares and eight octadecanuclear hexagons [102]. (Redrawn from X. Kong et al, A chiral 60-metal sodaUte cage featuring 26 vertex-sharing [Er4(p.3-OH)4] cubanes, Journal of the American Chemical Society, 131, 6918-6919, 2009.)...

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Next, (1) CO binds to Cluster C to yield a Credi-CO complex (2) CO undergoes attack by the metal-bound hydroxide and is oxidized to CO2 as Cluster C is reduced by two electrons to the Cred2 state (3) CO2 is released and a second CO molecule binds to Cluster C to form a Cred2-CO complex (4) electrons are transferred from Cred2-CO to reduce Cluster B as the second molecule of CO2 is released. This mecha-... 

However, while ruthenium carbonyl was found to decompose the formate ion in basic media, the rate was slower (<0.1 mmol trimethyl ammonium formate to H2 and C02 per hour) than the rate of the water-gas shift reaction (>0.4 mmol H2/hr) at 5 atm CO and 100 °C. Increasing CO pressure decreased the formate decomposition rate. However, it was observed that increasing the CO pressure from 5 atm CO to 50 atm increased the H2 production rate to 10 mmol/hr. They proposed, in a similar manner to Pettit et al.,34 a mechanism that involved nucleophilic attack by amine (instead of hydroxide). Activation of the metal carbonyl (e.g., Ru3(CO) 2 cluster to Ru(CO)5) was suggested to be favored by dilution, increases in CO pressure, or, in the case of Group VIb metal carbonyl complexes, photolytic promotion. The mechanism is shown below in Scheme 9 ... 

The mechanisms of CD processes can be divided into two different processes formation of the required compound by ionic reactions involving free anions, and decomposition of metal complexes. These two categories can be further divided in two formation of isolated single molecules that cluster and eventually form a crystal or particle, and mediation of a solid phase, usually the metal hydroxide. We consider first the pathways involving free anions and defer to later those where a metal complex decomposes. 

The chalcogenide precursors possess many talents. Apart from forming the chalcogenide ions, they also form complexes with metal ions. As noted at the beginning of this section, and ignoring the distinction between ion-by-ion and hydroxide cluster mechanisms treated previonsly, CD processes can be divided according to two basic mechanisms participation of free snlphide ions (the... 

Probably the least-known aspect of the CD process is what determines the nucle-ation on the substrate and the subsequent film growth. In considering this aspect, we will treat the ion-by-ion and hydroxide cluster mechanisms separately, although there will be many features in common. The principles discussed should be the same for both the free chalcogenide and the complex-decomposition mechanisms. 

The basic features of the ion-by-ion and hydroxide cluster film-forming mechanisms are shown schematically in Figures 2.1 and 2.2, respectively. Film formation involving complex decomposition will proceed in a similar manner (Fig. 2.3 shows this for a molecule-by-molecule deposition). 

Fig. 2.9 Transmission spectra of CD CdSe films deposited at various temperatures from CdS04/NTA/Na2SeS03 baths. All samples deposited by hydroxide cluster mechanism except 80°C HC (high complex), which proceeded via the ion-by-ion mechanism. The effective bandgap can be approximated by the wavelength (photon energy) a little shorter (higher) than the absorption onset. A second absorption knee, ca. 0.4 eV to higher energy of the initial onset, seen clearly in the 41 °C and 80°C samples, is due to a transition from the spin-orbit valence level to the lowest conduction level and is commonly observed in these films.

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