Abstract
The electronic structure and properties of the actinides in unusual oxidation states have been examined within the framework of quantum-chemical ideas. Hartree–Fock atomic calculations for the actinide series, and molecular orbital calculations for the octahedral oxyanions of uranium, neptunium, plutonium, and americium in high and highest oxidation states, and for the octahedral chloro-complexes of the actinides(III) and (IV) from protactinium to einsteinium, have been carried out. These calculations have been used to examine the possible existence of various new oxidation states of the actinides. A cation–cation interaction mechanism has been proposed. The characteristic features of the trans-effect in the chemistry of the actinides have been examined. New possibilities for using the Mössbauer isomer shifts at the actinide nuclei to interpret chemical properties have been demonstrated. The influence of relativistic effects on the chemical properties of the actinides has been analysed. In particular, it has been shown that the high value of the spin–orbit splitting is responsible for the gradual stabilisation and stability of the bivalent state at the end of the actinide series, the significant difference in the stability of the lanthanides(IV) and actinides(IV), and the possibility in principle of obtaining lanthanyl groups at the end of the lanthanide series.
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