Electronic Structure and Properties of Berkelium Iodates

Abstract

The reaction of Bk(OH) with iodate under hydrothermal conditions results in the formation of Bk(IO) as the major product with trace amounts of Bk(IO) also crystallizing from the reaction mixture. The structure of Bk(IO) consists of nine-coordinate Bk cations that are bridged by iodate anions to yield layers that are isomorphous with those found for Am, Cf, and with lanthanides that possess similar ionic radii. Bk(IO) was expected to adopt the same structure as M(IO) (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller Zr cation. Bk-O and Bk-O bond lengths are shorter than anticipated and provide further support for a postcurium break in the actinide series. Photoluminescence and absorption spectra collected from single crystals of Bk(IO) show evidence for doping with Bk in these crystals. In addition to luminescence from Bk in the Bk(IO) crystals, a broad-band absorption feature is initially present that is similar to features observed in systems with intervalence charge transfer. However, the high-specific activity of Bk (t = 320 d) causes oxidation of Bk and only Bk is present after a few days with concomitant loss of both the Bk luminescence and the broadband feature. The electronic structure of Bk(IO) and Bk(IO) were examined using a range of computational methods that include density functional theory both on clusters and on periodic structures, relativistic ab initio wave function calculations that incorporate spin-orbit coupling (CASSCF), and by a full-model Hamiltonian with spin-orbit coupling and Slater-Condon parameters (CONDON). Some of these methods provide evidence for an asymmetric ground state present in Bk that does not strictly adhere to Russel-Saunders coupling and Hund's Rule even though it possesses a half-filled 5f shell. Multiple factors contribute to the asymmetry that include 5f electrons being present in microstates that are not solely spin up, spin-orbit coupling induced mixing of low-lying excited states with the ground state, and covalency in the Bk-O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f ions such as Gd or Cm.

Contemporary Chemistry of Berkelium and Californium

“…The Bk III compounds possess large, broad bands in near-UV that have been assigned to Laporte allowed 5f!6d transitions. [47] Intraligand transitions for the Hdpa 1ligand in [Bk(Hdpa) 3 ]o verlap with the 5f!6d transitions. This broad feature is followed by a series of somewhat sharp 5f!5f transitions that are characteristic of Bk III .A se arly researchers noted, they are broader than expected.…”

“…}] and[ Cf(Hdpa)3 ] is not present in Bk III compounds with the same formula, and in [Bk(Hdpa)3 ]e ven if the exact same structurei sm aintained. However,l igand-field splitting in Bk III can parallel the large splittings observed in Cf III compounds, and contracted BkÀL bond lengths are also found as occurs in CfÀLb ondingm etrics.Ar eport on the structure, properties, and electronic structure of [Bk(IO 3 ) 3 ]a nd [Bk(IO 3 ) 4 ][47] rapidlyf ollowed that of [Bk{B 6 O 8 (OH)5 }] and[ Bk(Hdpa) 3 ]. The goal was to prepare [Bk(IO 3 ) 4 ]b ecause Bk IV possesses ah alf-filled5f 7 shell, but rapid reduction of the [Bk(OH) 4 ]o ccurredd uring the synthesis likely because of the combinationo fr adiolytic and chemical reactions that lead to formationo fB k III and crystallization of [Bk(IO 3 ) 4 ].…”

CONDON 3.0: An Updated Software Package for Magnetochemical Analysis‐All the Way to Polynuclear Actinide Complexes

“…To emphasize the subtleties in the various approaches to model exchange‐coupled actinide systems, the basics are briefly recapitulated. From a computational point of view, most of the essential information has been given in multiple works concerning mononuclear and polynuclear 5 f ‐electron systems …”

“…Utilizing the doped compounds means that coupling interactions are insignificant, and we thus can apply single‐ion models. Fitting the experimentally determined crystal‐field splitting with CONDON 3.0 to obtain the full set of ligand field parameters was recently reported by Silver et al The calculated ligand field parameters are used in the following sections for the model calculations of exchange‐coupled clusters (see Table ). …”

Advances in bonding and properties of inorganic systems from relativistic calculations in Latin America

“…Multiple factors contribute to the ground state asymmetry that includes 5f electrons being present in microstates that are not solely spin up, spin‐orbit coupling induced by mixing low‐lying excited states with the ground state, and covalency in the Bk(IV)‐O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f 7 ions such as Gd(III) or Cm(III) …”