Origin of Selectivity of a Triazinyl Ligand for Americium(III) over Neodymium(III).

[M(EtBTP)3][BPh4]3⋅3 CH3CN (M=Nd, Am; EtBTP=2,6‐bis(5,6‐diethyl‐1,2,4‐triazin‐3‐yl)pyridine) have been synthesized from reactions of MCl3⋅n H2O with EtBTP in acetonitrile followed by anion metathesis. Structural analysis reveals that these compounds contain M3+ cations bound by tridentate EtBTP ligands to create a tricapped trigonal prismatic geometry around the metal centers. Collection of high‐resolution, single‐crystal X‐ray diffraction data also allowed reduction in bond lengths esd's, such that a slight contraction of Δ=0.0158(18) Å in the Am−N versus Nd−N bond lengths was observed, even though these cations ostensibly have matching ionic radii. Theoretical evaluation revealed enhanced metal–ligand bonding through back donation in the [Am(EtBTP)3]3+ complex that is absent in [Nd(EtBTP)3]3+. Actinides versus lanthanides! Comparison of the NdIII and AmIII tris‐triazinyl complexes has revealed the nature of the selectivity for AmIII over lanthanides (see scheme). Theoretical evaluation revealed enhanced metal–ligand bonding through back donation in the [Am(EtBTP)3]3+ complex that is absent in [Nd(EtBTP)3]3+. [ABSTRACT FROM AUTHOR]