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

Abstract

M(EtBTP) 3 ][BPh 4 ] 3 ·3CH 3 CN (M = Nd, Am;EtBTP = 2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)pyridine) have been synthesized from reactions of MCl 3 ·n H 2 Ow ith EtBTP in acetonitrile followed by anion metathesis. Structural analysis reveals that these compounds contain M 3 + cations bound by tridentate EtBTP ligands to create at ricapped trigonal prismatic geometry around the metal centers. Collection of high-resolution,s ingle-crystal X-ray diffraction data also allowedr eductioni nb ond lengths esd's, such that as light contraction of D = 0.0158(18) in the AmÀNv ersus NdÀNb ond lengths waso bserved, even thought hese cationso stensibly have matchingi onic radii. Theoretical evaluation revealed enhanced metal-ligand bondingt hroughb ack donation in the [Am(EtBTP) 3 ] 3 + complex that is absentin[Nd(EtBTP) 3 ] 3 + .The importance of separating Am III from Ln III (Ln = lanthanide) cations stems from the need for more sensible ande fficient nuclear fuel cycles. The recycling of used nuclear fuel centers on the extraction of reusable uranium and plutonium through PUREX-like processes, and their re-use as mixed-oxide(MOX) nuclear fuels. [1] However,s toring the remaining waste after this extractioni sn on-trivial, because it is composed of fissionproducts, such as 90 Sr, 137 Cs, and lanthanides, as wella st he socalled minor actinides, neptunium, americium, and curium;t he latter actinides formed via neutron capture. After extraction of uranium and plutonium, the bulk of the waste consists of either stable isotopes or ones with relativelys hort half-lives, with notable long-lived exceptions that include 99 Tc (t1 = 2 = 2.11 10 5 years)a nd 135 Cs (t1 = 2 = 2.3 10 6 years).In contrast, americium is mostly presenti nt he form of 241 Am, which possesses an intermediate half-life of 432.2 years. Neutron capture and b decay processes primarily from the parenti sotope 241 Pu create > 1.3 kg of americium per ton of typical used nuclear fuel. [2] Thus, the term "minora ctinide" is inappropriate for americium and probably needs to be discard-ed in its entirety. Arguments can be made that it represents an energyr esourcef or fast neutron reactors, in which it can be fissioned, andt hat its removal from nuclear waste dramatically decreases the long-term radioactivity of ar epository.H owever, the primary driving force justifying its extraction is the heat load that it createsi nn uclear repository scenarios. Accordingly, separating americium from post-PUREX nuclear waste streams has becomeafocal point of radiochemicalinterest.Nitrogen-donor ligands, in contrastt ot raditional oxygen donors, such as phosphonates and organophosphates, have been the subjecto fi ncreased attention over the past several decades because of their potential use in f-block separations. These complexes possess the addedb enefito fi ncineration leadings olely to the formation of actinideo xides, thereby reducingt he volumeo fr adioactive waste in repositories. One particularly promising family of ligands that falls into this class are the tridentate, nit...

Comparative Investigation into the Complexation and Extraction Properties of Tridentate and Tetradentate Phosphine Oxide‐Functionalized 1,10‐Phenanthroline Ligands toward Lanthanides and Actinides

“…And to validate the possibility of formation the 1 : 3 species of trivalent actinides and lanthanides with tridentate L 2 , the 9‐coordinated 1 : 3 type Am III and Eu III complexes with L 2 were optimized using B3LYP method. Similar 1 : 3 Am III and lanthanide complexes have also been reported with other tridentate ligands like Et‐BTP [28] and N,O‐mixed diphenylphosphoryl ligands [29]…”

“…And to validate the possibility of formation the 1 : 3 species of trivalent actinides and lanthanides with tridentate L 2 , the 9-coordinated 1 : 3 type Am III and Eu III complexes with L 2 were optimized using B3LYP method. Similar 1 : 3 Am III and lanthanide complexes have also been reported with other tridentate ligands like Et-BTP [28] and N,O-mixed diphenylphosphoryl ligands. [29] As listed in Table 3, in these optimized 1 : 1 and 1 : 2 complexes of L 1 , the average Am-N L and Am-O L bond distances are slightly longer than their corresponding EuÀ N L and EuÀ O L bond distances, which can be ascribed to the slightly larger ionic radius of Am III (1.070 Å) than that of Eu III (0.995 Å).…”

Probing a variation of the inverse-trans-influence in americium and lanthanide tribromide tris(tricyclohexylphosphine oxide) complexes

“…Key elements within QTAIM were extracted such as the electron density, delocalization indices, and energy densities at the interatomic region (bond critical point, BCP) which have been employed previously for this aim. [40][41][42][43][44][45][46][47][48] The covalency was analyzed, on one hand, by changes in the concentration of the electron density at the BCP along with changes in the delocalization indices. On the other hand, energy densities show the polarization of the covalent bond by looking at the ratios between potential [V(r)] and kinetic [G(r)] energy densities, which for partial covalent bonds lie in between values of 1 and 2.…”

Probing the Inverse Trans Influence in Americium and Lanthanide Tribromide Tris(tricyclohexylphosphine oxide)

“…Key elements within QTAIM were extracted such as the electron density, delocalization indices, and energy densities at the interatomic region (bond critical point, BCP) which have been employed previously for this aim. [33][34][35][36][37][38][39][40][41] The covalency was analyzed, on one hand, by changes in the concentration of the electron density at the BCP along with changes in the delocalization indices. On the other hand, energy densities show the polarization of the covalent bond by looking at the ratios between potential [V(r)] and kinetic [G(r)] energy densities, which for partial covalent bonds lie in between values of 1 and 2.…”