Trapping an Unexpected/Unprecedented Hexanuclear Ce(III) Hydrolysis Product with Neutral 4-Amino-1,2,4-triazole

Using Ce(III) as both a representative lanthanide and actinide analog, the ability of mixtures of acidic and basic azoles to allow direct access to homoleptic N-donor f-element complexes in one pot reactions from hydrated salts as starting materials was examined by reacting mixtures of 4-amino-1,2,4-triazole (4-NH2-1,2,4-Triaz), 5-amino-tetrazole (5-NH2-HTetaz), and 1,2,3-triazole (1,2,3-HTriaz) in 1:1 and 1:3 ratios with CeCl3 center dot 7H(2)O, [C(2)mim](3)[CeCl6] ([C(2)mim](+) = 1-ethyl-2-methylimidazolium), and Ce(NO3)(3)center dot 6H(2)O. Although unsuccessful in our goal, structural analysis revealed that neutral 4-NH2-1,2,4-Triaz is structure directing via eta(2)mu(2)kappa(2) bridging, with the formation of the dinuclear complexes [Ce2Cl2(mu(2)-4-NH2-1,2,4-Triaz)(4)(H2O)(8)]Cl-4 center dot 4H(2)O, [Ce-2(mu(2)-4-NH2-1,2,4-Triaz)(4)(4-NH2-1,2,4-Triaz)(2)(Cl)(6)], and [4-NH2-1,2,4-HTriaz][Ce-2(mu(2)-4-NH2-1,2,4-Triaz)(2)(mu(2)-NO3)(NO3)(6)(H2O)(2)]. When the synthetic conditions favored hydrolysis, the hexanuclear Ce(III) complex [Ce-6(mu(3)-O)(4)(mu(3)-OH)(2)(mu(3)-Cl)(2)(Cl)(6)(mu(2)-4-NH2-1,2,4-Triaz)(12)]center dot 7H(2)O was isolated. This unexpected hydrolysis product represents the first example of a high nuclearity lanthanide complex where all Ln atoms are pairwise connected through 12 N-donor ligands or 12 neutral bridging ligands of any type, a rare example of incorporation of non-oxo coordinating anions in the M6X8 core, and the first reported Ce(III) hexanuclear complex of this type.Funding Agencies|Royal Swedish Academy of Science through the Goeran Gustafsson prize; Swedish Research Council [2020-05405]; Tage Erlander Guest Professorship [2018-00233]; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Elements program [DE-SC0019220]; U.S. NSF MRI [1828078]</p

Radium Revisited: Revitalization of the Coordination Chemistry of Nature’s Largest 2+ Cation

The crystallization, single-crystal structure, and Raman spectroscopy of Ra(NO3)2 have been investigated by experiment and theory, which represent the first, pure radium compound characterized by single crystal X-ray diffraction. The Ra2+ centers are bound by six chelating nitrate anions to form an anticuboctahedral geometry. The Raman spectrum acquired from a single crystal of Ra(NO3)2 generally occurs at a lower frequency than found in Ba(NO3)2 as expected. Computational studies on Ra(NO3)2 provide an estimation of the bond orders via Wiberg bond indices and indicate that Ra–O interactions are weak with values of 0.025 and 0.026 for Ra–O bonds. Inspection of natural bond orbitals and natural localized molecular orbitals suggest negligible orbital mixing. However, second-order perturbation interactions show that donation from the lone pairs of the nitrate oxygen atoms to the 7s orbitals of Ra2+ stabilize each Ra–O interaction by ca. 5 kcal mol−1

Coordination Chemistry and Spectroscopic Properties of Eu(II), Sm(II), and Yb(II) with 12-Crown‑4

The coordinative properties of 12-crown-4 (12c4) with Sm2+, Eu2+, and Yb2+ have been examined using nonaqueous and inert atmosphere conditions and led to the isolation of five complexes: Ln(12c4)(THF)2I2 (Ln = Sm 1, Eu 2), [Ln(12c4)2(CH3CN)][Ph4B]2 (Ln = Sm 3, Eu 4), and [Yb(12c4)2][Ph4B]2 (5). Most complexes were prepared via the salt metathesis of LnI2 with tetrabutylammonium tetraphenylborate ([TBA][Ph4B]) and 12-crown-4 in acetonitrile, while some were crystallized from THF. The half-sandwich compounds 1 and 2 crystallize with trans iodide orientation and exhibit mixed d–f and f–f and d–f photoluminescence when excited with 546 and 365 nm light, respectively. The full sandwich compounds 3 and 4 feature [Ln(12c4)2(CH3CN)]2+ complex cations, where two 12c4 molecules are not sufficiently large to coordinatively saturate these larger cations without further ligation, while the smaller Yb2+ cation is fully encapsulated in two 12c4 molecules (5). Solution UV–vis–NIR studies show that when 12c4 is added to acetonitrile solutions of LnI2, the f–d transitions shift to higher energies, suggesting destabilization of the lower lying d orbitals and increased stability of the divalent state by complexation to 12c4 in solution

Isolation of a Californium(II) Crown-Ether Complex

Californium (Z = 98) is the first member of the actinide series displaying metastability of the 2+ oxidation state. Understanding the origin of this chemical behavior requires characterizing Cf(II) materials, but isolating a complex with this state has remained elusive. The source of its inaccessibility arises from the intrinsic challenges of manipulating this unstable element as well as a lack of suitable reductants that do not reduce Cf(III) to Cf(0). Herein we show that a Cf(II) crown-ether complex, Cf(18-crown-6)I2, can be prepared using an Al/Hg amalgam as a reductant. While spectroscopic evidence shows that Cf(III) can be quantitatively reduced to Cf(II), rapid radiolytic re-oxidation back to the Cf(III) parent occurs and co-crystallized mixtures of Cf(II) and Cf(III) complexes are isolated if the crystallization is not conducted over the Al/Hg amalgam. Quantum chemical calculations show that the Cf‒ligand interactions are highly ionic and that 5f/6d mixing is absent, resulting in remarkably weak 5f→5f transitions and an absorption spectrum dominated by 5f→6d transitions