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

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

Synthesis, characterization, and high-pressure studies of a 3D berkelium(iii) carboxylate framework material

A berkelium(iii) mellitate, Bk-2[C-6(CO2)(6)](H2O)(8)center dot 2H(2)O, was synthesized and rapidly crystallized by reacting mellitic acid, C-6(CO2H)(6), and BkBr3 center dot nH(2)O in an aqueous medium. Single crystal X-ray diffraction shows that the compound crystallizes as a three-dimensional framework isostructural with Pu(iii), Am(iii), and Cm(iii) mellitates. UV-vis-NIR spectroscopic studies as a function of pressure were performed using a diamond anvil cell and show that the 5f -> 5f transitions of Bk3+ display enhanced hypsochromic shifting when compared to other An(iii) mellitates

Two Neptunium(III) Mellitate Coordination Polymers: Completing the Series Np-Cf of Trans-Uranic An(III) Mellitates

Two neptunium(III) mellitates, 237Np2(mell)(H2O)9 center dot 1.5H2O (Np-1 alpha) and 237Np2(mell)(H2O)8 center dot 2H2O (Np-1 beta), have been synthesized from 237NpCl4(dme)2 by reduction with KC8 and subsequent reaction with an aqueous solution of mellitic acid (H6mell). Characterization by single-crystal X-ray crystallography and UV-vis-NIR spectroscopy confirms that the neptunium is in its +3 oxidation state and both polymorphs are isostructural to the previously reported plutonium mellitates. Of the two morphologies, Np-1 alpha is indefinitely stable in air, while Np-1 beta slowly oxidizes over several months. This is due to the change in the energy of the metal-ligand charge-transfer absorption exhibited by these compounds attributed to differing numbers of carboxylate bonds to Np(III), where in Np-1 beta the energy is low enough to result in spontaneous oxidation

First Cationic Uranyl–Organic Framework with Anion-Exchange Capabilities

By controlling the extent of hydrolysis during the self-assembly process of a zwitterionic-based ligand with uranyl cations, we observed a structural evolution from the neutral uranyl–organic framework [(UO₂)₂(TTTPC)­(OH)­O­(COOH)]·1.5DMF·7H₂O (SCU-6) to the first cationic uranyl–organic framework with the formula of [(UO₂)­(HTTTPC)­(OH)]­Br·1.5DMF·4H₂O (SCU-7). The crystal structures of SCU-6 and SCU-7 are layers built with tetranuclear and dinuclear uranyl clusters, respectively. Exchangeable halide anions are present in the interlaminar spaces balancing the positive charge of layers in SCU-7. Therefore, SCU-7 is able to effectively remove perrhenate anions from aqueous solution. Meanwhile, the H₂PO₄^–-exchanged SCU-7 material exhibits a moderate proton conductivity of 8.70 × 10^–5 S cm^–1 at 50 °C and 90% relative humidity, representing nearly 80 times enhancement compared to the original material