| Abstrakt: |
EHMO-SCCC calculations have been used to probe the molecular orbital interactions of 1:1 and 2∶1 charge-transfer complexes of halobis( N,N-dialkyldithiocarbamato)iron(III) complexes with molecular halogens, treated as 'super molecules.' The molecular orbital structure of the compounds is being described in essentially the same way to that successfully applied in the cases of π-π, π-gs, and n- σ CT complexes. It is found that all types of orbital interactions ( σ- and/or π type) have a destabilizing effect on the complexes; hence, the forces of attachment have to be of the charge-transfer and van der Waals type, to offset this 'molecular orbital-based' repulsion. The relative stability of the compounds is broadly discussed in terms of the calculated binding energies, which are found to depend on the nature of both constituent molecules. Moreover, orbital populations, two-center energy terms, and computed atomic charges of the 'super molecules,' as compared to those of the constituent molecules, provide adequate information on the mechanism of the charge-transfer processes occurring upon complexation. It is important that weak bonding interactions between the constituent molecules do exist, but surprisingly directly, between the molecular halogens and the iron(III) central atoms, and not via the apical halogeno ligands. These bonding interactions, although not responsible for the stability of the compounds, account well for the observed magnetic behavior of the dimeric (2∶1) complexes and are of key importance in promoting intramolecular electron-transfer reactions responsible for the oxidation of half of the dithio ligands into the thiuram disulfides observed in some of the reactions of the iron(III) halobisdithiocarbamates with molecular halogens. [ABSTRACT FROM AUTHOR] |
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