Unusual Complexation Behaviors of R-BTPs with Water Molecule and Pd(II) Caused by Electronic Modulation of Substituents on BTP Backbone: New Insights Into Palladium Separation Under the Framework of Minor Actinides Partitioning
2,6-Bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (R-BTP) is one of the most promising classes of soft N-donor ligands for minor trivalent actinides (like Am(III), Cm(III) ) separation, but its complexation behavior with interfering element Pd(II) is still unknown. The substituents (R-) effect on the modulation of R-BTP’s complexation with Pd(II) were studied by single crystal diffractometry, 1H NMR spectroscopy, ESI-MS and density functional theory (DFT) calculation methods. The formation of both 1:1 and 2:1 complexes of R-BTP with Pd(II) were firstly identified and their electronic and geometric structures were determined. It has been found that modification of R-BTP skeleton with substituents (R-) changing from methyl (C1) to s-butyl (C4) leads to two different coordination models with water. The structure of 2:1 R-BTP/Pd(II) complexes is determined to be the unusual paramagnetic distorted six-coordinate compounds. However, the 1:1 species was found as a typical square-planar geometry. The extraction properties of Pd(II) and other fission or corrosion products by four R-BTPs were studied. This work can help to further understand the complexation behavior of Pd(II) with R-BTP, which provides theoretical insights for minor actinides and Pd(II) partitioning from high level active waste (HLW) using R-BTP type ligands.