The direct electrochemical synthesis of neutral and anionic halogen complexes of uranium(IV) and uranium(VI)

The electrochemical oxidation of anodic uranium into acetonitrile solutions of X₂ (X = Cl, Br) under nitrogen gives rise to UCl₄·4CH₃CN or UBr₄·2CH₃CN in good yield. These compounds are easily converted to other UX₄ adducts. In the presence of oxygen, solutions of UO₂X₂ are produced by the electrolysis, and the parent halide, or neutral addition compounds, are readily obtained from these. Addition of R₄NX to the cell results in the direct synthesis of (R₄N)₂UX₆ under nitrogen, or (R₄N)₂UO₂X₄ under oxygen. The only iodo compound which could be formed by electrolysis into N,N- dimethylformamide (=dmf) was UI₄·4dmf.     

Dioxouranium(VI) complexes of L-arginine

Complexes of dioxouranium(VI) with the amino acid L-arginine have been prepared and studied by ir and pmr measurements. The results indicate the formation of UO₂L XnH₂O (L = Arg^?; X = NO₃^?, CH₃COO^?, or ClO₄^?; n = 2 or 3). The bonding involves carboxylato-, amino-, and probably guanido groups of the ligand. The coordination sphere of dioxouranium(VI) also includes nitrate or acetate, but not the perchlorate group. Uranyl(VI) may reach the coordination number of 5 in the equatorial plane by the coordination of moleclues of H₂O.     

Synthesis, characterization and crystal structure of novel mononuclear peroxotungsten(VI) complexes. Insulinomimetic activity of W(VI) and Nb(V) peroxo complexes

Two new mononuclear peroxo complexes of tungsten of the formula (gu)₂[WO₂(O₂)₂] (1) and (gu)[WO(O₂)₂(quin-2-c)] (2a) (where gu⁺ = guanidinium ion, and quin-2-c = quinoline-2-carboxylate ion) have been synthesized and characterized by elemental analysis, infrared, Raman, UV-visible and ¹H NMR spectroscopies. The crystal structure of (gu)[WO(O₂)₂(quin-2-c)] · H₂O (2b) determined by X-ray diffraction indicates that the side-on peroxo groups and the bidentate quinaldate ligand bind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a counterion and the hydrogen-bound interactions stabilize the complexes. The in vitro insulin-mimetic effect of the complexes has been evaluated by the inhibitory effect on free fatty acid release in isolated fat adipocytes treated with epinephrine. Moreover the niobate analogues, synthesized and characterized previously, (gu)₃[Nb(O₂)₄] and (gu)₂[Nb(O₂)₃(quin-2-c)] · H₂O have been tested for the insulin-like activity.     

Ruthenium(VI) and osmium(VI) nitrido complexes with halogenated phenoxide and thiophenoxide ligands

Treatment of [Buⁿ₄N][Ru(N)Cl₄] with Na(OR) afforded [Buⁿ₄N][Ru(N)(OR)₄] (R = C₆F₅ (1), C₆F₄H (2), C₆Br₅ (3)), whereas that with [Buⁿ₄N][Os(N)Cl₄] gave [Buⁿ₄N][Os(N)(OR)₃Cl] (R = C₆F₅ (4), C₆F₄H (5), C₆Br₅ (6)). Treatment of [Buⁿ₄N][M(N)Cl₄] with Na(SC₆F₄H) and Na(Sxyl) (xyl = 2,6-dimethylphenyl) afforded [Buⁿ₄N][M(N)(SC₆F₄H)₄] (M = Ru (7), Os (8)) and [Buⁿ₄N][M(N)(Sxyl)₄] (M = Ru (9), Os (10)), respectively. The crystal structures of compounds 1, 6 and 9 have been determined.     

Oxovanadium(IV) and dioxouranium(VI) complexes with thiocarbohydrazones

Oxovanadium(IV) and dioxouranium(VI) complexes with thiocarbohydrazones have been prepared in an ethanolic medium and characterised by elemental analysis and molecular weight determination. They have 1:1 stoichiometry. The IR observations suggest that the ligands have coordinated through azomethine nitrogen atoms and reacted through hydroxy groups. The v(MN) and v(MO) vibrations have been assigned. The PMR spectral information supports the IR inference. The oxovanadium(IV) complexes show magnetic moments in the range of 1.74–1.94 B.M. The electronic spectra have been interpreted in the light of the BG model. Various NSH parameters have been calculated. The ESR spectra also render support for the spectral information. On the basis of this information it is suggested that oxovanadium(IV) complexes exhibit coordination number five and dioxouranium coordination number six.     

Synthesis and characterization of heteroscorpionate dioxo-tungsten(VI) complexes

Twelve new dioxo W(VI) complexes of a family of heteroscorpionate ligands of the type [(L)WO₂Y], where L = N₂X ligand and Y = Cl or OR, have been synthesized and characterized. With the more sterically bulky ligands we show that these complexes exist as isolable cis and trans isomers and compare the rate of such isomerization with their corresponding dioxo Mo(VI) analogs.     

The microwave synthesis of platinum(II) phosphine complexes

The microwave synthesis of a series of platinum(II) phosphine complexes is reported. The complexes dppePtCl₂ (dppe = bis(diphenylphosphino)ethane), dpppPtCl₂ (dppp = bis(diphenylphosphino)propane), dppmPtCl₂ (dppm = bis(diphenylphosphino)methane) and cis-(Ph₃P)₂PtCl₂ are synthesized from the reaction of potassium tetrachloroplatinate(II) and the phosphine. The isolated yields are 65% or better.     

Dioxouranium(VI) complexes with 2,6-acetylpyridinebenzoylhydrazones and -semicarbazones

Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H₂L¹), 2,6-diacetylpyridinebis(N4-phenylsemicarbazone) (H₂L²) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)(N4-phenylsemicarbazone) (H₂L³) give yellow products of the composition [UO₂(L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions.X-ray diffraction studies on [UO₂(L¹)(DMSO)], [UO₂(L²)], [UO₂(L²)(DMSO)] and [UO₂(L³)] show relatively short U-O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U-N bond lengths: 2.502(7)-2.671(7) Å). The addition of a sixth ligand to the equatorial coordination sphere results in a lengthening of the metal-pyridine bonds.     

Transesterification of oxo-osmium(VI) ligand complexes of thymine derivatives

We have measured the rate of transesterification reactions between glycols (L_O′) and oxo-osmium(VI) esters formed from thymine derivatives and a variety of nitrogen-containing ligands, L_OML_N, according to the equation: L_OML_N + L_O′

L_O′ML_N + L_O. We have also measured the rates of transesterification for this system with the addition of external nitrogen-containing ligands, L_N′. The order of effectiveness of the nitrogen-containing ligands in slowing the rate of transesterification is different depending on whether the ligand is present in the ester (L_N) or whether it is added externally (L_N′). Bathophenanthroline disulfonic acid is the most effective ligand when present in the ester. It forms exceptionally inert complexes. N,N,N′,N′-Tetramethylethylenediamine is the most effective ligand when added externally. The order of effectiveness of the nitrogen-containing ligand does not depend on the nature of either L_O or L_O′ but the nature of the glycol affects both the rate and the equilibria. We present mechanistic proposals, with limiting assumptions, to account for our findings.     

Multinuclear NMR study of the complexes of 6-phospho-D-gluconic acid with W(VI) and Mo(VI)

Multinuclear ((1)H, (13)C, (17)O, (31)P, (95)Mo, (183)W) magnetic resonance spectroscopy (1D and 2D) has been used to show that 6-phospho-d-gluconic acid forms three complexes with tungsten(VI) and six complexes with molybdenum(VI) in aqueous solution, depending on pH and concentration. Two isomeric 1:2 (metal-ligand) complexes are detected both with tungstate(VI) and molybdate(VI), having MO(2)(2+) centres and involving the carboxylate and the adjacent OH groups in addition to one 2:1 (metal-ligand) complex possessing a M(2)O(5)(2+) centre, with the ligand being coordinated by the carboxylate group and the three consecutive OH groups in positions 2, 3 and 4. Molybdate(VI) forms three additional species, which are not detected with tungstate. One of them is a 2:1 complex with a Mo(2)O(5)(2+) centre, with the ligand being tetradentate via O-3, O-4, O-5 and the phosphate group. The other two are 12:4 species, which can be seen as two 1:2 complexes bound together in a ring through two diphosphomolybdate moieties each derived from heptamolybdate by inclusion of two phosphate groups from the ligands.     

Neutral mononuclear dioxomolybdenum(VI) and dioxouranium(VI) complexes of oxolinic acid: Characterization and biological evaluation

The interaction of the first-generation quinolone antibacterial drug oxolinic acid (Hoxo) with the dioxomolybdenum(VI) and dioxouranim(VI) ions leads to the formation of the neutral mononuclear complexes MoO₂(oxo)₂ and UO₂(oxo)₂, respectively. The structure of the complexes has been characterized physicochemically and spectroscopically. The lowest energy model structure of the complexes has been determined with molecular modeling calculations. The antimicrobial activity of the complexes has been evaluated against three different microorganisms. The interaction of the complexes with calf-thymus DNA has been investigated with electronic and circular dichroism spectroscopies.     

Spectroscopic and structural characterizations of ammonium peroxo-carboxylato molybdate(VI) complexes

New ammonium derivatives of peroxo-carboxylato molybdenum(VI) complexes of general formula (NH₄)₂[MoO(O₂)₂(H_xL)] · nH₂O with L=oxalate (ox), citrate (cit), tartrate (tart), glycolate (glyc) and malate (mal) and (NH₄)₂[MoO₂(O₂)(L)] with L=oxalate (ox) have been prepared and characterized on the basis of elemental and thermal analysis as well as by IR and ¹³C NMR spectroscopy. These last two spectroscopic methods have been used to suggest the coordination mode of the ligand in the complexes. The X-ray crystal structures of the compounds (NH₄)₂[Mo₂O₂(O₂)₂(OH)₂(ox)₂], (NH₄)₂[MoO(O₂)₂(ox)] and (NH₄)₂[MoO(O₂)₂(glyc)] · 0.5EtOH have been determined, all showing a sevenfold-coordinated Mo atom with bidentate peroxides and carboxylate ligands.     

The triphenyltin(VI) complexes of NSAIDs and derivatives. Synthesis, crystal structure and antiproliferative activity. Potent anticancer agents

The novel triphenyltin(IV) esters of flufenamic acid (1), Hflu, [Ph₃Sn(flu)] (2), and of [2-(2,3-dichlorophenylamino)benzoic acid] (3), Hdcpa, [Ph₃Sn(dcpa)] (4) have been structurally characterized by means of vibrational and ¹H, ¹³C NMR spectroscopic studies. The crystal and molecular structures of [SnPh₃(dcpa)(DMSO)] 4a are described. The molecular structure of 4a reveals that the Sn atom has a distorted trigonal bipyramidal coordination geometry with equatorial phenyl groups and the carboxylate and dimethylsulfoxide oxygen atoms occupying axial positions. The crystal structure of 4a is self-assembled by C-H---π and π-π stacking interactions. The in vitro cytotoxic activity of 1-4 and of the related non-steroidal anti-inflammatory drugs, NSAIDs, [2-(2,6-dimethylphenylamino)benzoic acid], Hdmpa (5), [Ph₃Sn(dmpa)] (6), [2-(2,3-dimethylphenylamino)benzoic acid], mefenamic acid, Hmef (7) and [Ph₃Sn(mef)] (8) has been evaluated against the cancer cell lines MCF-7, T-24, A-549 and L-929. The ligands exhibited very poor cytotoxic activity against the four cancer cell lines. Complex 6 exhibits the highest activity and selectivity against A-549 and MCF-7 cancer cell lines and complex 8 the highest activity and selectivity against T-24 cancer cell line. The cytotoxic results indicate that coupling of Hdmpa and Hmef with R₃Sn(IV) metal center results in complexes with important biological properties and remarkable cytotoxic activity, since they display IC₅₀ values in a μΜ range better to that of the antitumor drug cis-platin. Complexes 6 and 8 are considered as excellent antitumor compounds and the results of this study represent the discovery of triphenyltin(IV)esters as a potential novel class of anticancer agents.     

Uranium(VI) complexes with phospholipid model compounds--a laser spectroscopic study

We present the complex formation of the uranyl ion (UO(2)(2+)) in the aqueous system with phosphocholine, O-phosphoethanolamine and O-phosphoserine. These phosphonates (R-O-PO(3)(2-)) represent the hydrophilic head groups of phospholipids. The complexation was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH=2-6. An increase of the fluorescence intensity, connected with a strong red-shift of about 8 nm compared to the free uranyl ion, indicates a complex formation between UO(2)(2+) and the phosphonates already at pH=2. Even at pH=6 these complexes prevail over the uranyl hydroxide and carbonate species, which are generated naturally at this pH. At pH=4 and higher a 1:2 complex between uranyl and O-phosphoserine was found. Complexes with a metal-to-ligand ratio of 1:1 were observed for all other ligands. Fluorescence lifetimes, emission maxima and complex stability constants at T=22+/-1 degrees C are reported. The TRLFS spectra of uranyl complexes with two phosphatidic acids (1,2-dimyristoyl-sn-glycero-3-phosphate and 1,2-dipalmitoyl-sn-glycero-3-phosphate), which represent the apolaric site of phospholipids, show in each case two different species.     

The synthesis and structural characterisation of two polynuclear hafnium(IV) complexes

Attempts to form extended supramolecular structures incorporating hafnium(IV) complexes of p-sulfonatocalix[6]arene resulted in the serendipitous formation of two polynuclear-hafnium clusters. Subsequent reaction between hafnium triflate and 1 M sulfuric or p-toluenesulfonic acid solutions also led to the formation of the same clusters, identified as cations based on Hf₁₇ and Hf₄, respectively.