No abstract

In this study, the synthesis, characterization, and pressure response of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate) coordination polymer, Cf2(mell)­(H2O)10·4H2O (Cf-1), are reported. The Cf–O lengths within the crystal structure are compared to its gadolinium (Gd-1) and holmium (Ho-1) analogs as well. These data show that the average Cf–O bond distance is slightly longer than the average Gd–O bond, consistent with trends in effective ionic radii. UV–vis-NIR absorption spectra as a function of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the Cf­(III) f → f transitions have a stronger dependence on pressure than that of the holmium analog. In the former case, the shift is nearly linear with applied pressure and averages 6.6 cm–1/GPa, whereas in the latter, it is <3 cm–1/GPa.

The mellitate ion is relevant in spent nuclear fuel processing and is utilized as a surrogate for studying the interactions of f elements with humic acids. A wealth of different coordination modes gives the potential for diverse structural chemistry across the actinide series. In this study, an americium mellitate, 243Am2[(C6(COO–)6]­(H2O)8·2H2O (1-Am), has been synthesized and characterized using structural analysis and spectroscopy at ambient and elevated pressures. 1-Am was then compared to isomorphous neodymium (1-Nd) and samarium (1-Sm) mellitates via bond-length analysis and pressure dependence of their Laporte-forbidden f → f transitions. Results show that the pressure dependence of the f → f transitions of 1-Am is significantly greater than that observed in 1-Nd and 1-Sm, with average shifts of 21.4, 4.7, and 3.6 cm–1/GPa, respectively. This greater shift found in 1-Am shows further evidence that the 5f orbitals are more affected than the 4f orbitals when pressure is applied to isostructural compounds.

The aqueous reaction of mellitic acid (H 6 mell) with 242 PuBr 3 •nH 2 O forms two plutonium mellitates, 242 Pu 2 (mell)-(H 2 O) 9 •H 2 O (Pu-1α) and 242 Pu 2 (mell)(H 2 O) 8 •2H 2 O (Pu-1β). These compounds are compared to the isomorphous lanthanide mellitates with similar ionic radii via bond length analysis. Both plutonium compounds form three-dimensional metal−organic frameworks, with Pu-1α having two unique metal centers and Pu-1β having one. All plutonium metal centers exhibit ninecoordinate geometries. Our results show metal−oxygen bond lengths for plutonium significantly shorter than those of the previously reported lanthanum and herein reported cerium analogues, consistent with the nine-coordinate ionic radii. Clear Laporte-forbidden 5f → 5f transitions are observed in the ultraviolet−visible−near-infrared spectra and are assigned to trivalent plutonium. However, there is a distinct color difference between the two plutonium compounds.

Using a redox-active dioxophenoxazine ligand, DOPO (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazine-9-olate), a family of actinide (U, Th, Np, and Pu) and Hf tris­(ligand) coordination compounds was synthesized. The full characterization of these species using 1H NMR spectroscopy, electronic absorption spectroscopy, SQUID magnetometry, and X-ray crystallography showed that these compounds are analogous and exist in the form M­(DOPOq)2(DOPOsq), where two ligands are of the oxidized quinone form (DOPOq) and the third is of the reduced semiquinone (DOPOsq) form. The electronic structures of these complexes were further investigated using CASSCF calculations, which revealed electronic structures consistent with metals in the +4 formal oxidation state and one unpaired electron localized on one ligand in each complex. Furthermore, f orbitals of the early actinides show a sizable bonding overlap with the ligand 2p orbitals. Notably, this is the first example of a plutonium–ligand radical species and a rare example of magnetic data being recorded for a homogeneous plutonium coordination complex.