Unusual structure, bonding and properties in a californium borate

Abstract

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations 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. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these 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.

Chirality and Polarity in the f‐Block Borates M4[B16O26(OH)4(H2O)3Cl4] (M=Sm, Eu, Gd, Pu, Am, Cm, and Cf)

“…In fact, it is only in the halides, [11][12][13][14][15][16] iodate, [17][18][19] triflate, [20][21][22][23] and borate [24][25][26][27][28] series that single-crystal X-ray diffraction data and complementary spectroscopy and theory span from thorium to californium. When the discussion is restricted to actinides in the + 3 oxidation state, the halides, iodates, and triflates are isomorphous with lanthanide analogues, and any changes in structure ostensibly correlates with changes in ionic radii.…”

“…[24] Under the same conditions, the middle-to-late trivalent actinides (Pu-Cm, Cf) yielded Pu[B 4 5 ]. [24][25][26][27][28] A more thorough discussion of the structural features of these compounds can be found elsewhere. [24][25][26][27][28] Within a borate network, the lanthanide and actinide series do not entirely parallel one another.…”

“…[24][25][26][27][28] A more thorough discussion of the structural features of these compounds can be found elsewhere. [24][25][26][27][28] Within a borate network, the lanthanide and actinide series do not entirely parallel one another. More importantly, the later trivalent actinides, Pu III , Am III , Cm III , and Cf III display different chemistry from one another as well.…”

“…[24] In contrast, Pu III uses its 6p orbital to bond with borate, [24] Am III and Cm III use the 6d, [24] whereas Cf III uses the 6d, 5f, and 7p. [28] In an effort to further probe the bonding in actinide borates, a new series of compounds has been synthesized from boric acid flux reactions. This system is saturated with chloride ions in an attempt to force interactions between chlorine and the felement centers.…”

Californium gleaming

“…Recently, a combination of theory and experiment has provided strong evidence that the 6d and 5f orbitals of mid-to-late actinides can be deliberately utilized to form covalent bonds, and that such bonding can differ substantially between neighbouring actinides, even if they are in the same oxidation state 4,5 . This ability to control bonding is the key to designing selective extractants and materials for trapping and differentiating radionuclides from nuclear waste, and shows that californium chemistry has a glowing future.…”