Cobalt rotational transitions

Figure 43 a shows the angular dependence of the four Co-ENDOR transitions for rotations of the crystal around three cartesian axes. For rotation I, the angular dependence shows a noteworthy peculiarity near

[Pg.86]

It was found that Zn[Co(CO)4]2 catalyzed the dimerization of norbor-nadiene to a new dimer in virtually quantitative yield (52). In substantiation of the working hypothesis, and assuming unrestricted rotation of the cobalt atoms in the Co—Zn—Co axis, the transition state in which the substrate molecules would come suflSciently close for bond formation is (XLVII), giving rise to the formation of only one dimer, endo-cis-endo heptaoyclo[5.3.1.1 . l -. O .O ]tetradecane, designated as Binor-S (XLVIII) (listed in Table II as (XXXIII)) (52) According to the lUPAC nomenclature rules, Binor-S is 1,2,4 5,6,8-dimetheno-a-indacene (59). 

Finally, on carrying the treatment of the concunent T2 and T2g crystal field potentials to all orders of perturbation theory, it has been established ), for a wide range of parameter sets, that the computed rotational strengths are at variance quantitatively and in qualitative form with the conesponding experimental values, measured from the CD band areas. In particular, the rotational strengths of the d—d transitions to the D3 cobalt(IIl) states, A2 and E with a common octahedral parent-... 

The systematic name is f"rtdo,ri.s, nrfo-heptacyclo[5.3.1.126.14-12.l9-".03-5.08 ll)]-tetradecane, designated Bisnor-S for short. In substantiation of the working hypothesis, and assuming unrestricted rotation of the cobalt atonfis in the Co-Zn-Co axis, the only transition state in which the substrate molecules would come sufficiently... 

Because they have low vapor pressures, transition metals cannot be loaded by direct adsorption, but their adsorption can be mediated by transient organo-metallic complexes formed between zerovalent metal atoms and solvent molecules. This is the basis of the solvated metal atom dispersion (SMAD) method developed by Klabunde and Tanaka [72]. Metal vapors condensed in Hquid hydrocarbons at low temperatures form weak complexes that are easily decomposed even below room temperature. Microporous supports impregnated with solutions of metal complexes at low temperatures are warmed up to decompose the complex and liberate zerovalent metal atoms which nucleate into clusters. Preparation of Ni- and Co-clusters in HY and HZSM-5 was reported [72]. In the same way, Nazar et al. [64] condensed iron and cobalt vapors in a slurry of dehydrated NaY zeolite in toluene at -120 °C, then the mixture was rotated at-78°C. The bis-toluene complex thus formed and adsorbed in the zeoUte was decomposed by warming to room temperature yielding clusters small enough to fit into supercages. 

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