Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States

Abstract

Pentavalent actinyl nitrate complexes AnO(NO) were produced by elimination of two NO from An(NO) for An = Pu, Am, Cm, Bk, and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO(NO) as AnO actinyl moieties coordinated by nitrates. Computations of alternative AnO(NO) and AnO(NO) revealed significantly higher energies. Previous computations for bare AnO indicated AnO for An = Pu, Am, Cf, and Bk, but CmO: electron donation from nitrate ligands has here stabilized the first Cm complex, CmO(NO). Structural parameters and bonding analyses indicate increasing An-NO bond covalency from Pu to Cf, in accordance with principles for actinide separations. Atomic ionization energies effectively predict relative stabilities of oxidation states; more reliable energies are needed for the actinides.

Contemporary Chemistry of Berkelium and Californium

“…Gas-phase studies on californium complexes have been used to investigate all oxidation states from Cf II to Cf V . [52,53] In the + II state these studies provide important comparisons with Sm II , which is the closeste lectrochemical analog of Cf II ,a nd similar gas-phase speciation was observed for Sm II and Cf II complexes. [54,55] Albeit, divalent californium chemistry has been historically somewhat developed in simple binary compounds such as halides, little else is known about californium's divalent character.…”

“…Gas-phase studiess how the increasing bond strengthf rom Pu to Cf with the decrease of symmetry. [52] Figure 5. EXAFS structure of An 3 + ions with DTPA.…”

“…Gas‐phase studies on californium complexes have been used to investigate all oxidation states from Cf II to Cf V . In the +II state these studies provide important comparisons with Sm II , which is the closest electrochemical analog of Cf II , and similar gas‐phase speciation was observed for Sm II and Cf II complexes .…”

Comparison of tetravalent cerium and terbium ions in a conserved, homoleptic imidophosphorane ligand field

“…Recent gas-phase work suggests that the range of accessible oxidation states in the condensed phases may extend beyond tetravalent ions to pentavalent lanthanide ions as well. [28][29][30] Herein, we report the synthesis and characterization of the isotypic tetravalent cerium equivalent of 2-Tb(PN*), [Ce 4+ (NP(1,2-bis-t Bu-diamidoethane)(NEt 2 )) 4 ], 2-Ce(PN*), and its trivalent precursor, [K][Ce 3+ (NP(1,2-bis-t Budiamidoethane)(NEt 2 )) 4 ], 1-Ce(PN*), (Scheme 1), and provide a systematic structural, spectroscopic, and electrochemical comparison of these complexes to understand ligand eld's effects across the series on the stability and electronic structure of tetravalent lanthanide ions. The nearly monotonic contraction of ionic size across the lanthanide series for a given oxidation state leads to few examples where a given structural type is held across the series.…”

The duality of electron localization and covalency in lanthanide and actinide metallocenes

“…[21][22][23][24] Taken together, these studies have raised more basic questions regarding whether the concept of a multicongurational ground state should apply to all f-element compounds, how it equates to more established models of metal-ligand covalency, 25 and how it is manifested by changes in chemical reactivity or magnetic behavior. Although Ce(C 8 H 8 ) 2 is prototypical, such fundamental questions pertain to all formal Ce 4+ compounds [26][27][28][29][30][31][32][33][34][35] and high valent lanthanide compounds, [36][37][38][39][40][41] ytterbium complexes, [42][43][44][45][46][47][48] and the transuranic actinocenes 15,17,49 and have implications throughout the periodic table for the electronic structure models used to describe bonding near the limits of chemically accessible oxidation states. 50,51 Improved theoretical models of bonding in these systems are needed to develop new ligands and innovative concepts in lanthanide/actinide separations for nuclear energy.…”