Structural and Electronic Properties of Nb(V), Ta(V), and Pa(V) Fluoride Complexes:The Influence of Relativistic Effects on the Group V Elements
Résumé
The aqueous fluoro complexes of niobium and tantalum were studied using synchrotron based extended X-ray absorption spectroscopy (EXAFS) as model systems for comparison of the structural and coordination chemistry of the Group V metals Nb, Ta and their pseudo-homologue Pa(V). The EXAFS indicate differences in the coordination chemistry of Nb and Ta in these systems that were not intuitive based on their similar charge and ionic radii. The Ta speciation is dominated by six and seven coordinate fluoro complexes, while the chemical speciation of Nb under the same conditions is dominated by its hydrolyzed oxyfluoride complexes. Quantum chemical computations were performed to more fully describe these observations and these results were compared to our earlier study on the fluoro complexes of protactinium. Computations performed with and without the inclusion of scalar relativistic effects reveal that the differences in the chemistry among the Group V elements, and their pseudo-homologue protactinium, are due to the increasing influences of relativistic effects as Z is increased from niobium to protactinium.