Pertechnetates - A Structural Study Across the Periodic Table.

The number of crystal structures of pertechnetates derived from aqueous solutions has been expanded from seven to over 30. We report the conversion of NH4TcO4 to aqueous HtcO4 via acidic cation exchange. This is followed by the synthesis and structural elucidation of pertechnetate salts of alkaline earth (AE), transition metal I and lanthanoids (Ln) elements. Various degrees of hydration and coordination are discussed. Where possible, a comparison with the perrhenate homologues is made. The described syntheses and materials may be used as novel starting materials for extended technetium research.

Influence of alkali metal cations on the formation of the heterobimetallic actinide tert-butoxides [AnM3(OtBu)7] and [AnM2(OtBu)6] (AnIV = Th, U; MI = Li, Na, K, Rb, Cs).

Heterobimetallic tert-butoxides of alkali metal cations with tetravalent actinide centers exhibit two distinctive structural motifs, [AnM2(OtBu)6] and [AnM3(OtBu)7] (AnIV = Th, U and MI = Li, Na, K, Rb, Cs), evidently governed by the size of the alkali metal ions. Both [AnM3(OtBu)7] AnM3 (AnIV = U, MI = Li; AnIV = Th, MI = Li, Na) and [AnM2(OtBu)6] AnM2 (AnIV = U, MI = Na-Cs; AnIV = Th, MI = K-Cs) compounds are obtained in nearly quantitative yields by reacting actinide and alkali metal silyl amides with an excess of tert-butyl alcohol. The AnM3 complexes form a cubane-type coordination motif, whereas the AnM2 complexes display a geometry resembling two face-shared bipyramids. The sodium derivatives of thorium and uranium (ThNa3 and UNa2) allow the determination of the structural transition threshold as a function of the ratio of the ionic radii ri(AnIV)/ri(MI). The AnM3 complexes are formed for ratios above 0.92 and the AnM2 type is formed for ratios below 0.87. All compounds are unambiguously characterized in both solution and solid states by NMR and IR spectroscopic studies and single crystal X-ray diffraction analyses, respectively.

High-Yield 99mTc Labeling of Gold Nanoparticles Carrying Atropine and Adrenaline.

This work focuses on the synthesis, purification, and analytical characterization of novel multifunctional Au NPs radiolabeled with 99mTc. These mixed-ligand shell Au NPs represent pharmacologically relevant samples for potential application in theragnostics. A ligand using a plain linker with a rather long chain consisting of 10 CH2 groups and a thiol moiety along with the PADA chelator has been used for both the attachment to the Au NP surface and for the 99mTc(CO)3+ complexation. We have combined this with our approach of stabilizing Au NP without any PEG or other stabilizing groups. Thus, monoligand shell Au NPs were radiolabeled by different strategies (prelabeling and postlabeling). Additionally, pharmacologically relevant Au NPs were synthesized carrying both a biofunctionalization with either atropine or adrenaline and the 99mTc radiolabel. All samples were obtained in very good yields (up to 80% of the total activity loaded onto the column) and completely/particularly purified using desalting columns. Detailed analytical characterization of the Au NPs before and after radiolabeling has proven the NPs' robustness throughout the process. Their intact functionalization, shape, and stability was confirmed by transmission electron microscopy (TEM), ultraviolet/visible (UV/vis) spectroscopy, dynamic light scattering (DLS), and infrared (IR) spectroscopy. The presented strategy represents a versatile building block system that can be adapted to a variety of bioactive molecules and may be of high relevance for theragnostic applications.

Heterobimetallic uranyl(VI) alkoxides of lanthanoids: formation through simple ligand exchange.

Lanthanoid and actinoid silylamides are versatile starting materials. Herein we show how a simple ligand exchange with tert-butanol leads to the formation of the first trimeric heterobimetallic uranyl(VI)-lanthanoid(III) alkoxide complexes. The µ3 coordination of the endogenous uranyl oxo atom results in a significant elongation of the bond length and a significant deviation from the linear uranyl arrangement.

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride.

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH4 )2 [TcO(OTf)5 ]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO3 (OTf)], and intermediate TcVI species. 99 Tc nuclear magnetic resonance (NMR) has been used to study the TcVII compound and electron paramagnetic resonance (EPR), 99 Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH4 )2 [TcO(OTf)5 ] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH4 )4 [{TcO(TcO4 )4 }4 ] ⋅10 H2 O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species.

Rhodium(III) Dihalido Complexes: The Effect of Ligand Substitution and Halido Coordination on Increasing Cancer Cell Potency.

This work presents the synthesis of eight new rhodium(III) dihalido complexes, [RhX2(L)(LH)] (where X = Cl or I), which incorporate two bidentate N-(3-halidophenyl)picolinamide ligands. The ligands have different binding modes in the complexes, whereby one is neutral and bound via N,N (LH) coordination, while the other is anionic and bound via N,O (L) coordination. The solid state and solution studies confirm multiple isomers are present when X = Cl; however, after a halide exchange with potassium iodide (X = I) the complexes exist exclusively as single stable trans isomers. NMR studies reveal the Rh(III) trans diiodido complexes remain stable in aqueous solution with no ligand exchange reported over 96 h. Chemosensitivity data against a range of cancer cell lines show two cytotoxic complexes, where L = N-(3-bromophenyl)picolinamide ligand. The results have been compared to the analogous Ru(III) complexes and overall highlight the Rh(III) trans diiodido complex to be ∼78× more cytotoxic than the analogous Rh(III) dichlorido complex, unlike the Ru(III) complexes which are equitoxic against all cell lines. Additionally, the Rh(III) trans diiodido complex is more selective toward cancerous cells, with selectivity index (SI) values >25-fold higher than cisplatin against colorectal carcinoma.

Correction: Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands.

Correction for 'Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands' by Anaïs Pitto-Barry et al., Dalton Trans., 2017, 46, 15676-15683.

Preparation of Heterobimetallic Ketimido-Actinide-Molybdenum Complexes.

During our attempts to prepare paddlewheel actinide-molybdenum complexes of the type [(X)An(MesNPR2)3Mo(CO)3] (Mes= 2,4,6-trimethylphenyl; X = Cl or I; An = U or Th; R = iPr or Ph) we have found that under certain conditions acetonitrile insertion reactions occur to give the heterobimetallic bridging ketimido species [ClAn(µ-MesNPiPr2)2(µ-MesNPiPr2{µ-NCMe})Mo(CO)3] (An = U, 1; Th, 2), [ClAn(µ-MesNPPh2)2(µ-MesNPPh2{µ-NCMe})Mo(CO)3] (An = U, 3; An = Th, 4), and [IAn(η2-MesNPiPr2)(µ-MesNPiPr2){µ-NC(Me)N(Mes)PiPr2}Mo(CO)3] (An = U, 5; Th, 6). Structural and spectroscopic data confirm the assignment of a ketimido ligand bridging An(IV) and Mo(0) centers. The isolation of 1-6 is in contrast to our previously reported preparations of [(X)An(MesNPPh2)3Mo(CO)3] (An = U or Th; X= Cl or I; Chem. Commun. 2018, 54, 13515-13518) with the difference in reactivity being attributable to a combination of ancillary phosphino-amide, reaction solvent, and temperature variation. Complexes 1-5 represent the first examples of structurally characterized ketimido-bridged actinide-transition metal linkages and demonstrate the profound differences in reaction outcomes that can occur from relatively minor experimental changes.

Fast, Facile and Solvent-Free Dry-Melt Synthesis of Oxovanadium(IV) Complexes: Simple Design with High Potency towards Cancerous Cells.

A range of oxobis(phenyl-1,3-butanedione) vanadium(IV) complexes have been successfully synthesized from cheap starting materials and a simple and solvent-free one-pot dry-melt reaction. This direct, straightforward, fast and alternative approach to inorganic synthesis has the potential for a wide range of applications. Analytical studies confirm their successful synthesis, purity and solid-state coordination, and we report the use of such complexes as potential drug candidates for the treatment of cancer. After a 24 hour incubation of A549 lung carcinoma cells with the compounds, they reveal cytotoxicity values elevenfold greater than cisplatin and remain non-toxic towards normal cell types. Additionally, the complexes are stable over a range of physiological pH values and show the potential for interactions with bovine serum albumin.

ß-Ketoiminato Iridium(III) Organometallic Complexes: Selective Cytotoxicity towards Colorectal Cancer Cells HCT116 p53-/.

This report presents a new library of organometallic iridium(III) compounds of the type [Cp*IrCl(L)] (Cp*=pentamethylcyclopentadienyl and L=a functionalized ß-ketoiminato ligand) showing moderate to high cytotoxicity against a range of cancer cell lines. All compounds show increased activity towards colorectal cancer, with preferential activity observed against the immortalized p53-null colorectal cell line, HCT116 p53-/-, with sensitivity factors (SF) up to 26.7. Additionally, the compounds have excellent selectivity for cancerous cells when tested against normal cell types, with selectivity ratios (SR) up to 35.6, contrary to that of cisplatin, which is neither selective nor specific for cancerous cells (SF=0.43 and SR=0.7-2.3). This work provides a preliminary understanding of the cytotoxicity of iridium compounds in the absence of p53 and has potential applications in treatment of cancers for which the p53 gene is absent or mutant.

Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study.

The uranyl(vi) 'Pacman' complex [(UO2)(py)(H2L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp2Ti(η2-Me3SiC[triple bond, length as m-dash]CSiMe3) and [Cp2TiCl]2 to oxo-titanated uranyl(v) complexes [(py)(Cp2TiIIIOUO)(py)(H2L)] 1 and [(ClCp2TiIVOUO)(py)(H2L)] 2. Combination of ZrII and ZrIV synthons with A yields the first ZrIV-uranyl(v) complex, [(ClCp2ZrOUO)(py)(H2L)] 3. Similarly, combinations of Ae0 and AeII synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)2(ClMgOUO)(py)(H2L)] 4, [(py)2(thf)2(ICaOUO)(py) (H2L)] 5; the zinc complexes [(py)2(XZnOUO)(py)(H2L)] (X = Cl 6, I 7) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(v) complexes; monomeric [(py)3(RbOUO)(py)(H2L)] 8 and hexameric [(MOUO)(py)(H2L)]6 (M = Rb 8b or Cs 9). In these uranyl(v) complexes, the pyrrole N-H atoms show strengthened hydrogen-bonding interactions with the endo-oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M4 edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(v) in 7 (ZnI)) to compare the covalent character in the UV-O and O-M bonds and show the 5f orbitals in uranyl(vi) complex A are unexpectedly more delocalised than in the uranyl(v) 7 (ZnI) complex. The Oexo-Zn bonds have a larger covalent contribution compared to the Mg-Oexo/Ca-Oexo bonds, and more covalency is found in the U-Oexo bond in 7 (ZnI), in agreement with the calculations.

Actinide-transition metal bonding in heterobimetallic uranium- and thorium-molybdenum paddlewheel complexes.

We report the preparation of four heterobimetallic uranium- and thorium-molybdenum paddlewheel complexes. The characterisation data suggest the presence of Mo → An σ-interactions in all cases. These complexes represent unprecedented actinide-group 6 metal-metal bonds, where before heterobimetallic uranium-metal bonds were restricted to group 7-11 metals.

Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands.

Half-sandwich metal complexes are of considerable interest in medicinal, material, and nanomaterial chemistry. The design of libraries of such complexes with particular reactivity and properties is therefore a major quest. Here, we report the unique and peculiar reactivity of eight apparently 16-electron half-sandwich metal (ruthenium, osmium, rhodium, and iridium) complexes based on benzene-1,2-dithiolato and 3,6-dichlorobenzene-1,2-dithiolato chelating ligands. These electron-deficient complexes do not react with electron-donor pyridine derivatives, even with the strong σ-donor 4-dimethylaminopyridine (DMAP) ligand. The Ru, Rh, and Ir complexes accept electrons from the triphenylphosphine ligand (σ-donor, π-acceptor), whilst the Os complexes were found to be the first examples of non-electron-acceptor electron-deficient metal complexes. We rationalised these unique properties by a combination of experimental techniques and DFT/TDFT calculations. The synthetic versatility offered by this family of complexes, the low reactivity at the metal center, and the facile functionalisation of the non-innocent benzene ligands is expected to allow the synthesis of libraries of pseudo electron-deficient half-sandwich complexes with unusual properties for a broad range of applications.

Axially Symmetric U-O-Ln- and U-O-U-Containing Molecules from the Control of Uranyl Reduction with Simple f-Block Halides.

The reduction of UVI uranyl halides or amides with simple LnII or UIII salts forms highly symmetric, linear, oxo-bridged trinuclear UV /LnIII /UV , LnIII /UIV /LnIII , and UIV /UIV /UIV complexes or linear LnIII /UV polymers depending on the stoichiometry and solvent. The reactions can be tuned to give the products of one- or two-electron uranyl reduction. The reactivity and magnetism of these compounds are discussed in the context of using a series of strongly oxo-coupled homo- and heterometallic poly(f-block) chains to better understand fundamental electronic structure in the f-block.

Inner-sphere vs. outer-sphere reduction of uranyl supported by a redox-active, donor-expanded dipyrrin.

The uranyl(vi) complex UO2Cl(L) of the redox-active, acyclic diimino-dipyrrin anion, L- is reported and its reaction with inner- and outer-sphere reductants studied. Voltammetric, EPR-spectroscopic and X-ray crystallographic studies show that chemical reduction by the outer-sphere reagent CoCp2 initially reduces the ligand to a dipyrrin radical, and imply that a second equivalent of CoCp2 reduces the U(vi) centre to form U(v). Cyclic voltammetry indicates that further outer-sphere reduction to form the putative U(iv) trianion only occurs at strongly cathodic potentials. The initial reduction of the dipyrrin ligand is supported by emission spectra, X-ray crystallography, and DFT; the latter also shows that these outer-sphere reactions are exergonic and proceed through sequential, one-electron steps. Reduction by the inner-sphere reductant [TiCp2Cl]2 is also likely to result in ligand reduction in the first instance but, in contrast to the outer-sphere case, reduction of the uranium centre becomes much more favoured, allowing the formation of a crystallographically characterised, doubly-titanated U(iv) complex. In the case of inner-sphere reduction only, ligand-to-metal electron-transfer is thermodynamically driven by coordination of Lewis-acidic Ti(iv) to the uranyl oxo, and is energetically preferable over the disproportionation of U(v). Overall, the involvement of the redox-active dipyrrin ligand in the reduction chemistry of UO2Cl(L) is inherent to both inner- and outer-sphere reduction mechanisms, providing a new route to accessing a variety of U(vi), U(v), and U(iv) complexes.

Correction: Inner-sphere vs. outer-sphere reduction of uranyl supported by a redox-active, donor-expanded dipyrrin.

[This corrects the article DOI: 10.1039/C6SC02912D.].

Subtle Interactions and Electron Transfer between U(III) , Np(III) , or Pu(III) and Uranyl Mediated by the Oxo Group.

A dramatic difference in the ability of the reducing An(III) center in AnCp3 (An=U, Np, Pu; Cp=C5 H5 ) to oxo-bind and reduce the uranyl(VI) dication in the complex [(UO2 )(THF)(H2 L)] (L="Pacman" Schiff-base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At-first contradictory electronic structural data are explained by combining theory and experiment. Complete one-electron transfer from Cp3 U forms the U(IV) -uranyl(V) compound that behaves as a U(V) -localized single molecule magnet below 4 K. The extent of reduction by the Cp3 Np group upon oxo-coordination is much less, with a Np(III) -uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np(IV) U(V) but single-crystal X-ray diffraction and SQUID magnetometry suggest a Np(III) -U(VI) assignment. DFT-calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu(III) -U(VI) interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.

Catalytic one-electron reduction of uranyl(VI) to Group 1 uranyl(V) complexes via Al(III) coordination.

Reactions between the uranyl(VI) Pacman complex [(UO2)(py)(H2L)] of the Schiff-base polypyrrolic macrocycle L and Tebbe's reagent or DIBAL result in the first selective reductive functionalisation of the uranyl oxo by Al to form [(py)(R2AlOUO)(py)(H2L)] (R = Me or (i)Bu). The clean displacement of the oxo-coordinated Al(III) by Group 1 cations has enabled the development of a one-pot, DIBAL-catalysed reduction of the U(VI) uranyl complexes to a series of new, mono-oxo alkali-metal-functionalised uranyl(V) complexes [(py)3(MOUO)(py)(H2L)] (M = Li, Na, K).