Synthesis and properties of a thermally stable methyltitanium(IV) compound: Cyclopentadienylmethyldichlorotitanium(IV)

η⁵C₅H₅Ti(CH₃)Cl₂ and η⁵-C₅H₅Ti(C₂H₅TiCl₂ have been synthesized. The reactivity of the methyl compound is much greater than that of the closely related sandwich compound, (η⁵-C₅H₅)₂Ti(CH₃)Cl, but the thermal stability is comparable.     

Synthesis and structural characterization of a molecular plutonium(IV) compound constructed from dimeric building blocks

Single crystals of Na(8)Pu(2)(O(2))(2)(CO(3))(6) x 12H(2)O, exhibiting bridging mu(2),eta(2)-O(2) ligands in unprecedented Pu(IV) dimeric units, were obtained at ambient temperature from an aqueous Pu(IV) peroxide carbonate solution.     

Kinetic studies on the reduction of a nickel (III) oxime-imine complex by sulphur(IV) and selenium(IV)

The kinetics of the reduction of [Ni^III(L¹)]²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02 and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC₂·H₂O and HSO ₃ ⁻ is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO ₃ ²⁻ seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of HSeO _l3 ⁻ is ≈ 10³ times slower than that of H₂SeO₃. The kinetic data indicate that the oxidation of sulphur(IV) by [Ni^IIIL¹)]²⁺ is much more favourable as compared to the corresponding oxidation of selenium(IV).     

An X-ray study of the complex anionbis(N-hydroxy-iminodiacetate) vanadate(IV), a model for a vanadium-containing biologic compound

The structure of ammonium tetramethylammoniumbis(N-hydroxy-iminodiacetate)vanadate(IV) was determined by x-ray analysis. One independent anion and two cations were found in the asymetric unit. The crystal is monoclinic, space group C2/c, with a=15.820(9), b=16.450(6), c=16.311(4) å,=118.92(3) deg., V=3715(3) å³, Z=8, D_x=1.56g cm^–3,(M_o-K_a)=5.59 cm^–1, F(OOO)=2028, M=434.9 for C₁₂H₂₄N₄O₁₀V. The structure was solved and refined to R(F)=0.029 and R_w(F)=0.040.The complex anion does not contain the oxovanadium(IV) group, but contains vanadium(IV) as the central atom. This is the first example of a vanadium(IV) complex octacoordinated to nitrogen and oxygen atoms exhibiting a highly distorted dodecahedral geometry. The chelation is along twoa and fourg edges. As the angles ones are bonding distances (N—O, 1.381(3), 1.382(4) å) the angles around the central atom are very different from those usually observed in the dodecahedral complexes. The V—O distances range from 1.973(3) to 2.071(3) å and the V—N distances range from 2.002(3) to 2.003(4) å.     

Dioxobridged complexes of molybdenum (IV) and tungsten (IV) with N-alkylphenothiazines and their interactions with L-cysteine and L-histidine

Six new dioxobridged complexes of molybdenum (IV) and tungsten (IV) with N-alkylphenothiazines having the general formula M₂O₄(L)₂(H₂O)₂ [where M = molybdenum or tungsten and L = N-alkylphenothiazines] have been synthesised. The complexes have been characterised on the basis of analytical, molar conductance, magnetic susceptibility, spectral data, TGA and DTA. The low magnetic moments for the complexes are due to spin-spin interaction or metal-metal bonding. The interactions of these complexes with some biologically important amino acids have been studied.     

Kinetic studies on the stripping of thorium (IV) and uranium (IV) from tributylphosphate-kerosene with dilute nitric acid solution

The cold solution of a pyrophosphate kit was prepared and dispensed into 2-ml fractions which were stored at −20°C for one week. The solution was prepared by using two protection methods. The first was nitrogen purging to exclude air and the second one the addition of the well known antioxydant ascorbic acid. The aim was to determine the stability of^99mTc(Sn)-PyP obtained by labeling these fractions prepared under the given experimental conditions. The content of^99mTc-pertechnetate in the unprotected samples raises with time. Nitrogen purging provides some protection but already after a few days the content of pertechnetate exceeds 5%. The addition of ascorbic acid gave good results. The content of pertechnetate was 1–2% after seven days in the presence of 50 μg of acid per ml of the cold kit.     

Preparation and characterization of diphenyllead(IV) and triphenyllead(IV) complexes with N-protected amino-acids and the dipeptides

The diphenyllead(IV) derivatives of N-benzoyl-(glycine, DL -alanine); N-formyl and N-acetyl-L -phenylalanine; N-monochloroacetyl-L -phenylalanine; N-benzoyl-(glycylglycine, DL -alanylglycine), and N-formyl- N-acetyl- and N-monochloroacetyl-(L -phenylalanylglycine) have been prepared in 1:2 molar ratio by reaction of diphenyllead dichloride with the appropriate amino-acid or dipeptide. Corresponding triphenyllead(IV) derivatives have been prepared in 1:1 molar ratio by reaction of triphenyllead chloride with the thallium(I) salts of the amino-acid or the dipeptide. These complexes have been characterized by elemental analysis, IR and ¹H NMR spectral studies. A polymeric hexacoordinated octahedral structure for diphenyllead(IV), and a five-coordinated distorted trigonalbipyramidal chain-type structure for triphenyllead(IV), complexes is confirmed by IR spectra. The carboxylate group acts in a bidentate manner, not as in diorgano and triorganotin(IV) complexes with these acids, where it is monodentate. The available bonding sites such as amide and peptide carbonyl (CO) and amide and peptide nitrogen atoms are not involved in bonding with lead (IV) and thus are available for bonding with the biological systems. The presence of different N-protecting groups does not affect the coordination sites around lead(IV). The triphenyllead(IV) compounds are relatively more stable than the diphenyllead(IV) compounds.     

Single crystal electron spin resonance of bis(tetraphenylphosphonium) bis(quinoxaline-2,3-dithiolato)oxovanadate(IV) as a pure compound and diluted in the isomorphous molybdenum(IV) compound

Single crystal e.s.r. spectra at room temperature and Q-band frequencies on [PPh₄]₂ [(Mo/V)O(qdt=₂] (qdt = quinoxaline-2,3-dithiolate) containing ca 3% vanadium gave the spin-Hamiltonian parameters g₁ = 1.977 ± 0.001, g₂ = 1.985 ± 0.001, g₃ = 1.987 ± 0.001, A₁ = (−38.5 ± 0.3) × 10⁻⁴, A₂ = (−45.1 ± 0.3) × 10⁻⁴, A₃ = (−133.2 ± 0.3) × 10⁻⁴ cm⁻¹, and Q′ = −(0.15±0.05) × 10⁻⁴ cm⁻¹. The g and A tensor axes are not coincident. The principal values of the g and A tensors have been analysed via an angular overlap treatment. Proton spin-flip transitions were observed in the spectra at X-band frequencies. Single crystal e.s.r. spectra of undiluted [PPh₄]₂ [VO(qdt)₂] at both X- and Q-band frequencies are interpreted in terms of a two-dimensional weak exchange model with J₀ = −48 ± 2G (ferromagnetic).     

Synthesis and characterization of a novel tetranuclear 5f compound: a new synthon for exploring U(IV) chemistry

In the course of structurally characterizing previously reported complexes based on the 1,2-bis(dimethylphosphino)ethane)) (dmpe) ligand ([(dmpe)(2)UCl(4)] (1) and [(dmpe)(2)UMe(4)] (2)), we find that adjusting the U/dmpe ratio leads to an unprecedented species. Whereas the use of two or three equivalents of dmpe relative to UCl(4) produces 1 as a blue-green solid, the use of a 1:1 dmpe/UCl(4) stoichiometry yields [(dmpe)(4)U(4)Cl(16)]·2CH(2)Cl(2)·(3·2CH(2)Cl(2)) as a green solid. In turn, 3 is used to prepare a mixed-chelating ligand complex featuring the bidentate ligand 4,4'-dimethyl-2,2'-bipyridine (dmbpy), [(dmpe)(dmbpy)UCl(4)] (4). The measured magnetic susceptibilities for 1-4 trend toward nonmagnetic ground states at low temperatures.     

Kinetic studies of the interaction between organotin(IV)chlorides and tetraaza Schiff bases: Synthesis and characterization of some novel tin(IV) Schiff base complexes

In this article the kinetics of the interaction between the teteraaza Schiff bases as donor with organotin(IV)chlorides as acceptor was studied in acetonitrile. Teteraaza Schiff bases are (Me₄‐Bzo₂[14]tetraeneN₄) (tmtaa), (Me₄‐4‐CH₃Bzo₂[14]tetraeneN₄) (Metmtaa), (Me₄‐4‐ClBzo₂[14]tetraeneN₄) (Cltmtaa), i.e., [(Me₄‐Bzo₂[14]tetraeneN₄)] means that (5,7,12,14‐tetramethyldibenzo[b,i][1,4,8,11] tetraazacyclotetradecine) (tmtaa) and organotin(IV)chlorides are methyltin(IV) trichloride, phenyltin(IV)trichloride, dimethyltin (IV)dichloride, diphenyltin(IV) dichloride, and dibutyltin(IV)dichloride. The kinetic parameters and the second‐order k₂ rate constants show the donor properties of tetraaza Schiff bases as Me₄‐4‐CH₃Bzo₂[14]tetraeneN₄ > Me₄‐Bzo₂[14]tetraeneN₄ > Me₄‐4‐ClBzo₂[14]tetraeneN₄ and also the acceptor properties of organotin(IV)chlorides as PhSnCl₃ > MeSnCl₃ > Ph₂SnCl₂ > Me₂SnCl₂ > Bu₂SnCl₂. An excellent linearity of k_obs vs. the molar concentration of the acceptor, the high span of k₂ values, the large negative values of ΔS^≠, and the low ΔH^≠ values suggest an associative (A) mechanism for the acceptor–donor interaction. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 247–254, 2011     

Synthesis,characterization and antimicrobial activities of triorganotin(IV) complexes with azo-azomethine carboxylate ligands: crystal structure of a tributyltin(IV) and a trimethyltin(IV) complex

Triorganotin(IV) complexes with polyaromatic azo-azomethine carboxylate ligands viz. 2-{4-hydroxy-3-[(2/4-hydroxyphenylimino)methyl]phenylazo}benzoic acids [H₃L¹/H₃L²] were synthesized by reacting the ligands with either bis-tri-n-butyltin(IV) oxide (for 1 and 4) or trimethyltin(IV) chloride in presence of triethylamine (for 2 and 5) or triphenyltin(IV) hydroxide (for 3 and 6). The complexes were characterized by elemental analysis, UV, IR, NMR, and mass spectrometry. NMR spectroscopic studies of the compounds suggested that the complexes adopt four-coordinate tetrahedral geometry around tin in solution. Molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. Both complexes have distorted trigonal bipyramidal geometry around tin in the solid state. Compound 1 is a one-dimensional (1-D) double chain coordination polymer which can be described as two different 24- and 30-membered non-porous macrocyclic rings constructed from two tributyltin units and two ligand moieties. The structure of 2 comprises a discrete cyclic centrosymmetric dimer with two lattice water molecules per formula unit. In the dimer, two trimethyltin entities are bridged by two ligand moieties. The dimers are further interconnected with lattice water molecules by multiple O–H?O hydrogen bonds to form a 1-D H-bonded network. The complexes were also screened for their antimicrobial activities.     

Kinetic study of the reaction betweentrans-tetracyanodioxomolybdate(IV) and fluoride ions

Summary The kinetics of the reaction between [MoO₂(CN)₄]^4– and F^– have been studied in the pH range 8 to 11. The results indicated that the diprotonated form, [MoO(OH₂)(CN)₄]^2–, is the only reactive species and that the aqua-ligand is substituted by the F^– ion according to the following reaction. The k₁ and k_–1 values are 8.8(2) M^–1 s^–1 and 0.6(1)s^–1, respectively, at 15°C. A dissociative substitution process is proposed.     

A mixed-valence polyoxovanadate(III,IV) cluster with a calixarene cap exhibiting ferromagnetic V(III)-V(IV) interactions

A series of compounds (cat)[V6O6(OCH3)8(calix)(CH3OH)] was obtained under anaerobic conditions and solvothermal reaction of VOSO4 with p-tert-butylcalix[4]arene (calix) in methanol using different types of bases (Et4NOH, NH4OH, pyridine, Et3N). All compounds contain the same polyoxo(alkoxo)hexavanadate anion [V6O6(OCH3)8(calix)(CH3OH)]- (1) exhibiting a mixed valence {VIIIVIV5O19} core with the so-called Lindqvist structure coordinated to a calix[4]arene macrocycle and cocrystallizing with the conjugated acid of the base (cat = Et4N+, NH4(+), pyridinium, Et3NH+) involved in the synthesis process. The structures have been fully established from X-ray diffraction on single crystals and the mixed valence state has been confirmed by bond valence sum calculations. The magnetic behavior of all compounds are the same because of the polyalkoxohexavanadate anion [V6O6(OCH3)8(calix)(CH3OH)]- (1) and have been interpreted by DFT calculations. Thus the V(III)...V(IV) interactions are found to be weakly ferromagnetic (<5.5 cm(-1)) while the V(IV)...V(IV) are antiferromagnetic (-17.6; -67.6 cm(-1)). The set of the coupling exchange parameters allows a good agreement with the magnetic experimental data.     

Bis(diisopropylammonium) thiosulfate and bis(tert‐butylammonium) thiosulfate

Two new dialkylammonium thiosulfates, namely bis(diisopropylammonium) thiosulfate, 2C₆H₁₆N⁺·S₂O₃²⁻, (I), and bis(tert‐butylammonium) thiosulfate, 2C₄H₁₂N⁺·S₂O₃²⁻, (II), have been characterized. The secondary ammonium salt (I) crystallizes with Z = 4, while the primary ammonium salt (II), with more hydrogen‐bond donors, crystallizes with Z = 8 and a noncrystallographic centre of inversion. In both salts, the organic cations and thiosulfate anions are linked within extensive N—H...O and N—H...S hydrogen‐bond networks, forming extended two‐dimensional layers. Layers are parallel to (10) in (I) and to (002) in (II), and have a polar interior and a nonpolar hydrocarbon exterior. The layered structure and hydrogen‐bond motifs observed in (I) and (II) are similar to those in related ammonium sulfates.     

Studies of glutathione transferase P1-1 bound to a platinum(IV)-based anticancer compound reveal the molecular basis of its activation

Platinum-based cancer drugs, such as cisplatin, are highly effective chemotherapeutic agents used extensively for the treatment of solid tumors. However, their effectiveness is limited by drug resistance, which, in some cancers, has been associated with an overexpression of pi class glutathione S-transferase (GST P1-1), an important enzyme in the mercapturic acid detoxification pathway. Ethacraplatin (EA-CPT), a trans-Pt(IV) carboxylate complex containing ethacrynate ligands, was designed as a platinum cancer metallodrug that could also target cytosolic GST enzymes. We previously reported that EA-CPT was an excellent inhibitor of GST activity in live mammalian cells compared to either cisplatin or ethacrynic acid. In order to understand the nature of the drug-protein interactions between EA-CPT and GST P1-1, and to obtain mechanistic insights at a molecular level, structural and biochemical investigations were carried out, supported by molecular modeling analysis using quantum mechanical/molecular mechanical methods. The results suggest that EA-CPT preferentially docks at the dimer interface at GST P1-1 and subsequent interaction with the enzyme resulted in docking of the ethacrynate ligands at both active sites (in the H-sites), with the Pt moiety remaining bound at the dimer interface. The activation of the inhibitor by its target enzyme and covalent binding accounts for the strong and irreversible inhibition of enzymatic activity by the platinum complex.     

Synthesis and evaluation of carbamate prodrugs of a phenolic compound

A series of carbamates of the phenolic compound 1 were prepared and evaluated in vivo as its prodrug. Each carbamate was orally administered to rats, and plasma concentrations of the parent compound 1 were measured with the passage of time. We judged which carbamate was suitable for the prodrug of 1 from both the AUC value of 1 and absence of the carbamate in plasma. The AUC value of 1 after oral administration of 2b was approximately 40-fold higher than that for an administration of 1, and the bioconversion from 2b to 1 was excellent. As a whole, di-substituted carbamates resulted in higher plasma concentrations of 1 than did mono-substituted ones. However di-substituted carbamates were almost always detected in plasma. As a result, we found that the ethycarbamoyl derivative 2b demonstrates the best prodrug property in this series.     

Complexation of Thorium(IV) and Uranium(IV) by a Hexaacetic Hexaaza Macrocycle: Kinetic and Thermodynamic Topomers of Actinide Chelates with a Large Cavity Ligand

The solution behavior of the Th(IV) chelate with a polyaza polycarboxylic ligand, HEHA (1,4,7,10,13,16-hexaazacyclooctadecane-N,N ',N ",N "',N ",N "'-hexaacetic acid), is investigated by one- and two-dimensional NMR spectroscopy. [Th(HEHA)](2)(-) exhibits a very unusual irreversible topomerization process from a kinetically stable topomer of C(2) symmetry to a thermodynamically stable topomer of remarkably high symmetry (S(6)). The metal ion appears to be 12-coordinated in both geometries with a pseudoicosahedral arrangement of the chelating groups. The activation energy of the irreversible topomerization is exceedingly high (199 kJ.mol(-)(1)), and the slow kinetics of conversion is assigned to a complete reorganization of the chelate. U(IV) forms directly a stable entity of C(2) symmetry with HEHA and no reorganization of the complex is observed. The unusual topomerization phenomenon undergone by HEHA, is thus strongly dependant on the ionic radius of the encapsulated metal ion. The corresponding lanthanide chelates are totally asymmetric.     

Thermodynamic and Kinetic Parameters of Cerium(IV) Complexes with Some Dicarboxylic Acids

The thermodynamic and kinetic parameters of the cerium(IV) complexes formed in the initial stage of oxidation of dicarboxylic acids (H₂L), like pentanedioic, butanedioic, propanedioic, and ethanedioic acids, by cerium(IV) sulfate were studied by the spectrophotometric and pH-potentiometric methods with the aid of integral kinetic methods at an ionic strength I = 2 mol/L within the pH range of–0.3–1.6 in a sulfuric acid medium and at temperature of 293.15 K. The composition of these complexes, the form of organic ligand existence therein, the thermodynamic parameters of their formation, and the kinetic parameters of their intramolecular redox decomposition were determined. Linear correlations between the found thermodynamic and kinetic parameters of the examined complexes [CeOHL]⁺ were obtained. The rate equation of the redox process occurring in the systems Ce⁴⁺–H₂L was established and the corresponding reaction model was considered.