Characterization of berkelium(III) dipicolinate and borate compounds in solution and the solid state (original) (raw)
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Electronic Structure and Properties of Berkelium Iodates
The reaction of 249 Bk(OH) 4 with iodate under hydro-thermal conditions results in the formation of Bk(IO 3) 3 as the major product with trace amounts of Bk(IO 3) 4 also crystallizing from the reaction mixture. The structure of Bk(IO 3) 3 consists of nine-coordinate Bk III cations that are bridged by iodate anions to yield layers that are isomorphous with those found for Am III , Cf III , and with lanthanides that possess similar ionic radii. Bk(IO 3) 4 was expected to adopt the same structure as M(IO 3) 4 (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller Zr IV cation. Bk III −O and Bk IV −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 3) 4 show evidence for doping with Bk III in these crystals. In addition to luminescence from Bk III in the Bk(IO 3) 4 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 249 Bk (t 1/2 = 320 d) causes oxidation of Bk III and only Bk IV is present after a few days with concomitant loss of both the Bk III luminescence and the broadband feature. The electronic structure of Bk(IO 3) 3 and Bk(IO 3) 4 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 IV that does not strictly adhere to Russel−Saunders coupling and Hund's Rule even though it possesses a half-filled 5f 7 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 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 .
Unusual structure, bonding and properties in a californium borate
Nature Chemistry, 2014
The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations have demonstrated the involvement of 6p, 6d, and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. In this work, we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and that substantially rearrange upon complexation. A ligand that suits both of the above desired properties is polyborate. We demonstrate that the 5f, 6d, and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal field effects are present. Synthetic, structural, and spectroscopic data are complemented by quantum mechanical calculations to support these observations.
Rigorous probing of the electronic structure of Berkelium and Californium actinide atoms
2022
A recent experiment identified a weak spin-orbit-coupling in atomic Bk while a jj coupling scheme described atomic Cf. It concluded that these observations strengthen Cf as a transitional element in the actinide series. This paper uses Ramsauer-Townsend (R-T) minima and shape resonances (SRs) from low-energy electron elastic total cross sections (TCSs) calculated using the rigorous Regge pole method as novel confirmation of the observation. Regge pole-calculated TCSs for Bk and Cf atoms are characterized generally by ground, metastable and excited states negative-ion formation, R-T minima and SRs. Additionally, a polarization-induced metastable TCS with a deep R-T minimum near threshold characterizes the Bk TCSs, which flips over to a well pronounced SR appearing very close to threshold in the Cf TCSs. This demonstrates the sensitivity of R-T minima and SRs to the electronic structure of these atoms, thereby permitting their first time ever use as novel and rigorous validation of the experimental observation. .
Ca 3 Be 6 B 5 O 16 F: the first alkaline-earth beryllium borate with fluorine anions
The first all-alkaline-earth beryllium borate with fluorine anions, Ca 3 Be 6 B 5 O 16 F, was synthesized by a spontaneous crystallization flux method using LiF-B 2 O 3 as the flux. The structural framework of Ca 3 Be 6 B 5 O 16 F is composed of the inter-connected [Be 6 B 3 O 16 ] and [BO 3 ] fundamental building blocks, with [CaO 7 F] distorted polyhedra located in the interstitial sites. The [Be 6 B 3 O 16 ] group is discovered for the first time in beryllium borates. The UV-Vis-NIR diffuse-reflectance spectrum demonstrates that its UV cutoff edge is below 200 nm, and this is confirmed by first-principles studies. Thermal analysis reveals an incongruent feature at 1321 K. IR spectroscopy measurements are consistent with the crystallographic study. These data reveal that the crystal could have an application as a deep-ultraviolet optical material. † Electronic supplementary information (ESI) available: Crystallographic data of Ca 3 Be 6 B 5 O 16 F. See
American Mineralogist, 2012
Borate minerals composed of [Bφ 3 ] triangles and/or [Bφ 4 ] tetrahedra (φ = O or OH) commonly exhibit complex polymerizations to form diverse polyanion groups. High-resolution solid-state magic angle spinning (MAS) 11 B and 25 Mg NMR spectroscopy at moderate to ultrahigh magnetic fields (9.4, 14.1, and 21.1 T) allows for very accurate NMR parameters to be obtained for the borate dimorphs, inderite, and kurnakovite, [MgB 3 O 3 (OH) 5 •5H 2 O]. Improved agreement between experimental results and ab initio density functional theory (DFT) calculations using Full Potential Linear Augmented Plane Wave (FP LAPW) with WIEN2k validates the geometry optimization procedures for these minerals and permits refinements of the hydrogen positions relative to previous X-ray diffraction crystal structures. In particular, the optimized structures lead to significant improvements in the positions of the H atoms, suggesting that H atoms have significant effects on the 11 B and 25 Mg NMR parameters in inderite and kurnakovite. This study shows that combined high-resolution NMR spectroscopy and ab initio theoretical modeling provides an alternative method for the refinement of crystal structures, especially H positions.
Acta crystallographica. Section E, Structure reports online, 2014
The title compounds, K(+)·C7H7BF3O(-), (I), and K(+)·C6H4BF4 (-), (II), are mol-ecular salts containing para-substituted phenyl-tri-fluorido-borate anions. In each compound, the B atom adopts a distorted tetra-hedral BCF3 geometry. Despite their different compositions and space groups, the irregular KF8 coordination polyhedra of the potassium cations in the structures are almost identical. These polyhedra share faces and edges, generating infinite (010) layers in (I) and infinite (001) layers in (II). In (I), adjacent layers are stacked in an AAA… fashion, whereas in (II), they are stacked in an ABAB… sequence.
Redetermination of the crystal structure of potassium lead hexanitrocuprate(II), K2PbCu(NO2)6
Inorganic Chemistry, 1971
The structure of potassium lead hexanitrocuprate(II), K2PbCu(N0~)6, has been redetermined p i n g three-dimensional X-ray data and anisotropic thermal parameters. The space group is Fm3, with a0 = 10.672 (1) A. The calculated density for four formula units in the unit cell is 3.42 g/cm3; 1366 reflections, of which 464 are independent, were collected with an automated four-circle diffractometer. The structure was refined by full-matrix least-squares techniques to a conventional R factor of 0.028. The hexanitrocuprate ion has Th symmetry in apparent violation of the Jahn-Teller theorem, but the thermal parameters of $lie nitrogen atom are in accord withsthe assumption of a dynamic Jahn-Teller effect. The Cu-N bond length is 2.111 (4) A, the N-0 bond length is 1.260 (4) A, and the 0-3-0 angle is 117.9 (4)". KzSrCU(NOz)6 has also been prepared and it is n o t isomorphous with KzPbCu(N0~)e but with Kd3aCu(NOz)s.