NMR and TRLFS studies of Ln(iii) and An(iii) C5-BPP complexes

Christian Adam; Björn B Beele; Andreas Geist; Udo Müllich; Peter Kaden; Petra J Panak

doi:10.1039/c4sc03103b

NMR and TRLFS studies of Ln(iii) and An(iii) C5-BPP complexes

Chem Sci. 2015 Feb 1;6(2):1548-1561. doi: 10.1039/c4sc03103b. Epub 2014 Dec 19.

Authors

Christian Adam^{1

2}, Björn B Beele^{1

2}, Andreas Geist¹, Udo Müllich¹, Peter Kaden¹, Petra J Panak^{1

2}

Affiliations

¹ Karlsruhe Institute of Technology (KIT) , Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640 , 76021 Karlsruhe , Germany . Email: christian.adam@kit.edu.
² University of Heidelberg , Institute of Physical Chemistry , Im Neuenheimer Feld 253 , 69120 Heidelberg , Germany.

Abstract

C5-BPP is a highly efficient N-donor ligand for the separation of trivalent actinides, An(iii), from trivalent lanthanides, Ln(iii). The molecular origin of the selectivity of C5-BPP and many other N-donor ligands of the BTP-type is still not entirely understood. We present here the first NMR studies on C5-BPP Ln(iii) and An(iii) complexes. C5-BPP is synthesized with 10% ¹⁵N labeling and characterized by NMR and LIFDI-MS methods. ¹⁵N NMR spectroscopy gives a detailed insight into the bonding of C5-BPP with lanthanides and Am(iii) as a representative for trivalent actinide cations, revealing significant differences in ¹⁵N chemical shift for coordinating nitrogen atoms compared to Ln(iii) complexes. The temperature dependence of NMR chemical shifts observed for the Am(iii) complex indicates a weak paramagnetism. This as well as the observed large chemical shift for coordinating nitrogen atoms show that metal-ligand bonding in Am(C5-BPP)₃ has a larger share of covalence than in lanthanide complexes, confirming earlier studies. The Am(C5-BPP)₃ NMR sample is furthermore spiked with Cm(iii) and characterized by time-resolved laser fluorescence spectroscopy (TRLFS), yielding important information on the speciation of trace amounts of minor complex species.