Co4 i

Figure 8. Structure drawing of the tetranuclear cobalt(II) species (Co4(/i-dmpz)()(/i4-0)], 179. Based on data from (134).]...

Phosphine substituted derivatives of [004(00) 2 reported this year include polymeric products with dppe, identified spectroscopically, structurally characterised species [Co4 (C0)9 j Lj ] (n - 1,2 L PMe3 n - 2. L2 dppm) and species [Co4(solution structure and dynamics have been studied. 

Cluster lCo4(structurally characterised and the stereochemical non-rigidity of species [Co4(studied kinetically by using VT C n.m.r. spectroscopy.Ligand transfer between [Fe2 [Pg.173]

Dynamic mechanical properties also evolve gradually during the LST of polymeric systems. The gel point is reached when tan S becomes independent of frequency [58, 63, 65, 120, 149, 150] (see Eq. 4-12). Lines of tan 3(l) at several frequencies a>i, co2, co3, co4, co5, etc. decay gradually and intersect at the gel point (see Fig. 26). The method is very effective. The instant of gelation can be measured as precisely as the accuracy of the rheometer permits - a significant... 

On the basis of the very low Ag content, from the Co4.6AgO.2AF Rietveld refinement (Fig.5) Col, Co2 and also Ag2 were attributed to Co2+, whereas Ag5 must be partially occupied by Co2+ (for simplicity, site Ag2 will be indicated in Fig 5 and called Co4 from now on). As expected, no metallic Ag° was detected. After catalytic testing a fairly similar distribution of the 3.2 extraframework cations per unit cell was found. The most remarkable modification induced by the dry-wet SCR cycle was the migration of Co atoms from the Co2 to the Co4 site, an effect of particular interest as Co4 is, as stated earlier, nearer than Co2 to the Co2a position, i.e. the most active oc-site. 

Parallel results were obtained by UV-Vis DRS spectra (not reported).Calcined Co4.6AgO.2AF showed (i) absorptions at 444 and 520 nm, assigned to Colb and Cola sites, respectively, (ii) a band around 660 nm due to tetrahedral Co2+ ions in Co2a sites, (iii) the absence of bands due to Ag reduced clusters. After catalytic tests two absorptions below 400 nm and above 700 nm, ascribed to Co oxides species, arose and bands at 583 and 650 nm increased, indicating the migration of Co2+ ions to tetrahedral sites (Ciambelli et al., 2001). 

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