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...
Efforts to quantitatively reduce CfIII → CfII in solution as well as studies of its cyclic voltammetry have been hindered by its scarcity, significant challenges associated with manipulating an unusually intense γ emitter, small reaction scales, the need for nonaqueous solvents, and its radiolytic effects on ligands and solvents. In an effort to overcome these impediments, we report on the stabilization of CfII by encapsulation in 2.2.2-cryptand and comparisons with the readily reducible lanthanides, Sm3+, Eu3+, and Yb3+. Cyclic voltammetry measurements suggest that CfIII/II displays electrochemical behavior with characteristics of both SmIII/II and YbIII/II. The °E 1/2 values of −1.525 and −1.660 V (vs Fc/Fc+ in tetrahydrofuran (THF)) for [Cf(2.2.2-crypt)]3+/2+ and [Sm(2.2.2-crypt)]3+/2+, respectively, are similar. However, the ΔE values upon complexation by 2.2.2-cryptand for CfIII/II more closely parallels YbIII/II with postencapsulation shifts of 705 and 715 mV, respectively, whereas the shift of SmIII/II (520 mV) mirrors that of EuIII/II (524 mV). This suggests more structural similarities between CfII and YbII in solution than with SmII that likely originates from more similar ionic radii and local coordination environments, a supposition that is corroborated by crystallographic and extended X-ray absorption fine structure measurements from other systems. Competitive-ion binding experiments between EuIII/II, SmIII/II, and YbIII/II were also performed and show less favorable binding by YbIII/II. Connectivity structures of [Ln(2.2.2-cryptand)(THF)][BPh4]2 (Ln = EuII, SmII) are reported to show the important role that THF plays in these redox reactions.
The merging of small‐scale syntheses and rapid crystallization methods have provided access to crystalline samples of berkelium (Z=97) and californium (Z=98) coordination complexes and compounds that can be interrogated with a suite of spectroscopic tools and structural elucidation approaches that have come online over the last 20 years. The combination of this experimental data with relativistic theoretical methods that capture the effects of spin‐orbit coupling and scalar relativistic effects have allowed us to understand the electronic structure of berkelium and californium compounds at a level of detail that was not previously possible. The harbinger of this new era of post‐curium chemistry was the synthesis and characterization of [Cf{B6O8(OH)5}]. This compound possesses a structure type that is distinct from earlier actinide borates, a reduction in coordination number for californium, contracted Cf−O bond lengths, a substantially reduced magnetic moment with respect to the calculated free‐ion moment and, most importantly, vibronically coupled broadband photoluminescence. Ligand‐field analysis also showed that the splitting of the ground state was larger than typically found in the f‐block elements, and when taken together places its overall electronic structure as a hybrid of d‐ and f‐block components. The discovery of the unusual properties of this compound has led to the development of large families of 4f and 5f coordination complexes, in an effort to uncover the underlying origin of the electronic structure oddities, and whether there really is a sharp onset of these changes at californium. This in turn pushed the development of far more challenging berkelium chemistry (from a radiologic standpoint) because the half‐life of the isotopes decreases from 351 years for 249Cf to 330 days for 249Bk. This short review details some of the chemistry that has been reported over the last 15 years, and its consequences for understanding the periodic table.
The reaction of SmI2 with dibenzo-30-crown-10 (DB30C10), followed by metathesis with [Bu4N][BPh4], allows for the isolation of [SmII(DB30C10)][BPh4]2 as bright-red crystals in good yield. Exposure of [Sm(DB30C10)]2+ to solvents containing trace water results in the conversion to the dinuclear SmIII complex, Sm2(DB30C10)(OH)2I4. Structural analysis of both complexes shows substantial rearrangement of the crown ether from a folded, Pac-Man form with SmII to a twisted conformation with SmIII. The optical properties of [SmII(DB30C10)][BPh4]2 exhibit a strong temperature dependence and change from broad-band absorption features indicative of domination by 5d states to fine features characteristic of 4f → 4f transitions at low temperatures. Examination of the electronic structure of these complexes via ab initio wave function calculations (SO-CASSCF) shows that the ground state of SmII in [SmII(DB30C10)]2+ is a 4f6 state with low-lying 4f55d1 states, where the latter states have been lowered in energy by ∼12 000 cm–1 with respect to the free ion. The decacoordination of the SmII cation by the crown ether is responsible for this alteration in the energies of the excited state and demonstrates the ability to tune the electronic structure of SmII.
A dithiopicolinamide analog selectively extracts Am(iii) over Eu(iii) under acidic conditions.
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