Pure oxygen coordination

The synthesis of a variety of /3-diketonato complexes of Tc has been described. None of these compounds has been structurally described, but they are formulated as [TcO(/3-diketonate)2-Clj. A further variant of purely oxygen-coordinated Tc results from use of the Klaui-ligand (IS). Yellow-green complexes of composition [(Lor)TcOC12] were prepared by reaction of [TcOJ in the presence of cone. HCl with the ligand (18). 

Figure 4. Coordination of CO to Ni via pure oxygen coordination (a) triplet coupled orbitals (A and A ) oxygen lone pairs forming dative bonds to Ni (panels B and C) (b) schematic diagram of the many-electron wave function.

The elements with such an electronic configuration known as luminescent centers are Cr, Mn and They are capable of substituting in a wide variety of metal oxide host systems. They are invariably oxygen-coordinated with six nearest neighbors, and may be in a pure octahedral or a distorted octahedral symmetry site. These luminescent centers exists in a d configuration (Fig. 5.23), and the electronic repulsion, which results from placing three electrons in the same set of d-orbitals yields several states identified as free... 

Our results for the three coordination modes considered here indicate that the CO2 molecule prefers to adopt either a mixed carbon-oxygen coordination (III) or a pure coordination ( ) to the metal center, while a pure carbon coordination ( ) appears to be unfavorable. Further, the results suggest a rather weak CO - transition metal bond consistent with the low stability of adsorbed CO and CO2 in molecular complexes. 

Figure 5. Diffuse Reflectance Spectra at 293K of [Fe2(HPTP)(OH) (N03)2] - MMT and tBHP the maxima around 580 nm are assigned to peroxo-to-Fe " charge transfer. The pure complex shows a shoulder around 630 nm probably due to a (p-OH) or (p-OR)-to- Fe " charge transfer. The latter shoulder typically occurs close to the site of oxygen coordination. The binuclear iron(III) HPTP complexes are known to form blue-violet adducts with H2O2 in a 1 1 ratio, the complex being surprisingly more unstable than the HPTB complex [10,18].

Samples B, C and D, where the molybdenum has been introduced via the carbonyl complex, do not show a distinct oxygen coordination shell. The Mo atoms are coordinated by sulfur (almost) exclusively. Mo-Mo contacts are also visible for these samples (Fig. 8b-d) however, they are much weaker than in pure M0S2 (Fig. 8e). The missing Mo neighbors indicate a high dispersion of the Mo/S clusters in the zeofites [64,65]. 

Depending on the specific reaction conditions, complex 4 as well as acylium ion 5 have been identified as intermediates with a sterically demanding substituent R, and in polar solvents the acylium ion species 5 is formed preferentially. The electrophilic agent 5 reacts with the aromatic substrate, e.g. benzene 1, to give an intermediate cr-complex—the cyclohexadienyl cation 6. By loss of a proton from intermediate 6 the aromatic system is restored, and an arylketone is formed that is coordinated with the carbonyl oxygen to the Lewis acid. Since a Lewis-acid molecule that is coordinated to a product molecule is no longer available to catalyze the acylation reaction, the catalyst has to be employed in equimolar quantity. The product-Lewis acid complex 7 has to be cleaved by a hydrolytic workup in order to isolate the pure aryl ketone 3. 

In contrast to pure SsO, the adduct contains an SsO ligand with the oxygen atom in an equatorial position. The coordination at the metal atom is... 

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