Comparison of Americium(III) and Neodymium(III) Monothiophosphate Complexes

Mixed-donor ligands, such as those containing a combination of O/N or O/S, have been studied extensively for the selective extraction of trivalent actinides, especially Am3+ and Cm3+, from lanthanides during the recycling of used nuclear fuel. Oxygen/sulfur donor ligand combinations also result from the hydrolytic and/or radiolytic degradation of dithiophosphates, such as the Cyanex class of extractants, which are initially converted to monothiophosphates. To understand potential differences between the binding of such degraded ligands to Nd3+ and Am3+, the monothiophosphate complexes [M(OPS(OEt)2)5(H2O)2]2- (M3+ = Nd3+, Am3+) were prepared and characterized by single-crystal X-ray diffraction and optical spectroscopy and studied as a function of pressure up to ca. 14 GPa using diamond-anvil techniques. Although Nd3+ and Am3+ have nearly identical eight-coordinated ionic radii, these structures reveal that while the M-O bond distances in these complexes are almost equal, the M-S distances are statistically different. Moreover, for [Nd(OPS(OEt)2)5(H2O)2]2-, the hypersensitive 4I9/2 → 4G5/2 transition shifts as a function of pressure by -11 cm-1/GPa. Whereas for [Am(OPS(OEt)2)5(H2O)2]2-, the 7F0 → 7F6 transition shows a slightly stronger pressure dependence with a shift of -13 cm-1/GPa and also exhibits broadening of the 5f → 5f transitions at high pressures. These data likely indicate an increased involvement of the 5f orbitals in bonding with Am3+ relative to that of Nd3+ in these complexes.

Investigation of Pressure Effects in the Bimetallic Transplutonium Tetrazolate Complexes [(An(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·nH2O (An3+ = Cm3+, Bk3+, and Cf3+)

Understanding the effects of pressure on actinide compounds is an integral part of safe nuclear waste storage in deep geologic repositories and provides a means of systematically altering the structure and properties. However, detailing how the effects of pressure evolve across the actinide series in the later elements is not typically undertaken because of the challenges of conducting research on these unstable isotopes. Here, a family of bimetallic actinide complexes, [(An(pmtz)2(H2O)3)2(μ-pmtz)]2(pmtz)2·nH2O (An3+ = Cm3+, Bk3+, and Cf3+, pmtz- = 5-(pyrimidyl)tetrazolate; Cm1, Bk1, and Cf1), are reported and represent the first structurally characterized bimetallic berkelium and californium compounds. The pressure response as determined from UV-vis-NIR transitions varies for Cm1, Bk1, and Cf1. The 5f → 5f transitions in Cm1 are notably more sensitive to pressure compared to those in Bk1 and Cf1 and show substantial bathochromic shifting of several 5f → 5f transitions. In the case of Bk1, an ingrowth of a metal-to-ligand charge-transfer transition occurs at elevated pressures because of the accessible Bk3+/Bk4+ couple. For Cf1, no substantial transition shifting or emergence of MLCT transitions is observed at elevated pressures because of the prohibitive energetics of the Cf3+/Cf4+ couple and reduced sensitivity of the 5f → 5f transitions to the local coordination environment because of the more contracted 5f shell versus Cm3+ and Bk3+.

Transformation of Mononuclear Plutonium(III) Tetrazolate Complexes into Dinuclear Complexes in the Solid State

The salt metathesis reaction of Na(pmtz)·H2O [pmtz- = 5-(pyrimidyl)tetrazolate] and PuBr3·nH2O in an aqueous media leads to the formation of the mononuclear compound [Pu(pmtz)3(H2O)3]·(3 + n) H2O (Pu1, n = ∼8) that is isotypic with the lanthanide compounds [Ln(pmtz)3(H2O)3]·(3 + n) H2O (Ln = Ce-Nd). Dissolution and recrystallization of Pu1 in water yields the dinuclear compound {[Pu(pmtz)2(H2O)3]2(μ-pmtz)}2(pmtz)2·14H2O (Pu2), which is isotypic with the lanthanide compounds {[Ln(pmtz)2(H2O)3]2(μ-pmtz)}2(pmtz)2·14H2O (Ln = Nd and Sm). Like their nine-coordinate ionic radii, the M-O and M-N bond lengths in Pu1/Pu2 and Nd1/Nd2, respectively, are within error of one another. The Laporte-forbidden 4f → 4f and 5f → 5f transitions are also assigned in the UV-vis-NIR spectra for these f-element tetrazolate coordination compounds.

Crystal structure of 1-(2,6-diiso-propyl-phen-yl)-1H-imidazole

The crystal structure of the title compound, C15H20N2 or DippIm, is reported. At 106 (2) K, the mol-ecule has monoclinic P21/c symmetry with four mol-ecules in the unit cell. The imidazole ring is rotated 80.7 (1)° relative to the phenyl ring. Inter-molecular stabilization primarily results from close contacts between the N atom at the 3-position on the imidazole ring and the C-H bond at the 4-position on the neighboring DippIm, with ar-yl-aryl distances outside of the accepted distance of 5 Å for π-stacking.

Effect of methylene versus ethylene linkers on structural properties of tert-butyl and mesityl bis(imidazolium) bromide salts

The crystal structures of ligand precursor bis­(imidaozolium) salts 1,1′-methyl­enebis(3-tert-butyl­imidazolium) dibromide monohydrate, C₁₅H₂₆N₄⁺·2Br⁻·H₂O or [^tBuNHC₂Me][Br]₂·H₂O, 1,1′-(ethane-1,2-di­yl)bis­(3-tert-butyl­imidazolium) dibromide dihydrate, C₁₆H₂₈N₄⁺·2Br⁻·2H₂O or [^tBuNHC₂Et][Br]₂·2H₂O, 1,1′-methyl­enebis[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide dihydrate, C₂₅H₃₀N₄²⁺·2Br⁻·2H₂O or [^MesNHC₂Me][Br]₂·2H₂O, and 1,1′-1,1′-(ethane-1,2-di­yl)bis­[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide tetra­hydrate, C₂₆H₃₂N₄²⁺·2Br⁻·4H₂O or [^MesNHC₂Et][Br]₂·4H₂O, are reported. At 293 K, [^tBuNHC₂Me][Br]₂·H₂O crystallizes in the P2₁/c space group, while [^tBuNHC₂Et][Br]₂·2H₂O crystallizes in the P2₁/n space group at 100 K. At 112 K, [^MesNHC₂Me][Br]₂·2H₂O crystallizes in the ortho­rhom­bic space group Pccn while [^MesNHC₂Et][Br]₂·4H₂O crystallizes in the P2₁/c space group at 100 K.

The crystal structures of ligand precursor bis­(imidazolium) salts 1,1′-methyl­enebis(3-tert-butyl­imidazolium) dibromide monohydrate, C₁₅H₂₆N₄⁺·2Br⁻·H₂O or [^tBuNHC₂Me][Br]₂·H₂O, 1,1′-(ethane-1,2-di­yl)bis­(3-tert-butyl­imidazolium) dibromide dihydrate, C₁₆H₂₈N₄⁺·2Br⁻·2H₂O or [^tBuNHC₂Et][Br]₂·2H₂O, 1,1′-methyl­enebis[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide dihydrate, C₂₅H₃₀N₄²⁺·2Br⁻·2H₂O or [^MesNHC₂Me][Br]₂·2H₂O, and 1,1′-(ethane-1,2-di­yl)bis­[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide tetra­hydrate, C₂₆H₃₂N₄²⁺·2Br⁻·4H₂O or [^MesNHC₂Et][Br]₂·4H₂O, are reported. At 293 K, [^tBuNHC₂Me][Br]₂·H₂O crystallizes in the P2₁/c space group, while [^tBuNHC₂Et][Br]₂·2H₂O crystallizes in the P2₁/n space group at 100 K. At 112 K, [^MesNHC₂Me][Br]₂·2H₂O crystallizes in the ortho­rhom­bic space group Pccn while [^MesNHC₂Et][Br]₂·4H₂O crystallizes in the P2₁/c space group at 100 K. Bond distances and angles within the imidazolium rings are generally comparable among the four structures. All four bis­(imidazolium) salts co-crystallize with one to four mol­ecules of water.

Synthesis, structural analysis, and docking studies with SARS-CoV-2 of a trinuclear zinc complex with N-phenylanthranilic acid ligands

The structure of a trinuclear zinc complex, hexakis(μ₂‐2‐anilinobenzoato)diaquatrizinc(II), [Zn₂(C₁₃H₁₀NO₂)₆(H₂O)₂] or (NPA)₆Zn₃(H₂O)₂ (NPA is 2‐anilinobenzoate or N‐phenylanthranilate), is reported. The complex crystallizes in the triclinic space group P and the central Zn^II atom is located on an inversion center. The NPA ligand is found to coordinate via the carboxylate O atoms with unique C—O bond lengths that support an unequal distribution of resonance over the carboxylate fragment. The axial H₂O ligands form hydrogen bonds with neighboring molecules that stabilize the supramolecular system in rigid straight chains, with an angle of 180° along the c axis. π stacking is the primary stabilization along the a and b axes, resulting in a highly ordered supramolecular structure. Docking studies show that this unique supramolecular structure of a trinuclear zinc complex has potential for binding to the main protease (M^pro) in SARS‐CoV‐2 in a different location from Remdesivir, but with a similar binding strength.

Crystal structures of two dioxomolybdenum complexes stabilized by salan ligands featuring phenyl and cyclohexyl backbones

Two cis-dioxomolybdenum complexes based on salan ligands with different backbones are reported. The first complex, dioxido{2,2′-[l,2-phenylenebis(iminomethylene)]bis(phenolato)}molybdenum(VI) dimethylformamide disolvate, [Mo(C20H18N2O2)O2]·2C3H7NO (PhLMoO2, 1b), features a phenyl backbone, while the second complex, (6,6′-{[(cyclohexane-1,2-diyl)bis(azanediyl)]bis(methylene)}bis(2,4-di-tert-butylphenolato))dioxidomolybdenum(VI) methanol disolvate, [Mo(C36H56N2O2)O2]·2CH3OH (CyLMoO2, 2b), is based on a cyclohexyl backbone. These complexes crystallized as solvated species, 1b·2DMF and 2b·2MeOH. The salan ligands PhLH2 (1a) and CyLH2 (2a) coordinate to the molybdenum center in these complexes 1b and 2b in a κ2 N,κ2 O fashion, forming a distorted octahedral geometry. The Mo—N and Mo—O distances are 2.3475 (16) and 1.9567 (16) Å, respectively, in 1b while the corresponding measurements are Mo—N = 2.3412 (12) Å, and Mo—O = 1.9428 (10) Å for 2b. A key geometrical feature is that the N—Mo—N angle of 72.40 (4)° in CyLMoO2 is slightly less than that of the PhLMoO2 angle of 75.18 (6)°, which is attributed to the flexibility of the cyclohexane ring between the nitrogen as compared to the rigid phenyl ring in the PhLMoO2.

A five-coordinate cobalt bis-(di-thiol-ene)-phosphine complex [Co(pdt)2(PTA)] (pdt = phenyl-dithiol-ene; PTA = 1,3,5-tri-aza-7-phosphaadamantane)

The synthesis and crystal structure are reported for a five-coordinate cobalt di­thiol­ene-phosphine complex [Co(pdt)₂(PTA)] (pdt = phenyl­dithiol­ene; S₂C₂Ph₂), produced by PTA ligand-induced cleavage of the cobalt bis­(di­thiol­ene) dimer [Co₂(pdt)₄].

The title compound, bis­(1,2-diphenyl-2-sulfanyl­idene­ethane­thiol­ato-κ²S,S′)(1,3,5-tri­aza-7-phosphaadamantane-κP)cobalt(II) dichloromethane hemisolvate, [Co(pdt)₂(PTA)]·0.5C₂H₄Cl₂ or [Co(C₁₄H₁₀S₂)₂(C₆H₁₂N₃P)]·0.5C₂H₄Cl₂, contains two phenyl­dithiol­ene (pdt) ligands and a 1,3,5-tri­aza-7-phosphaadamantane (PTA) ligand bound to cobalt with the solvent 1,2-di­chloro­ethane mol­ecule located on an inversion center. The cobalt core exhibits an approximately square-pyramidal geometry with partially reduced thienyl radical monoanionic ligands. The supra­molecular network is consolidated by hydrogen-bonding inter­actions primarily with nitro­gen, sulfur and chlorine atoms, as well as parallel displaced π-stacking of the aryl rings. The UV–vis, IR, and CV data are also consistent with monoanionic di­thiol­ene ligands and an overall Co^II oxidation state.