Reactivity studies on Fe(III)-(O2(2-))-Cu(II) compounds: influence of the ligand architecture and copper ligand denticity

Heme-Cu/O2 adducts are of interest in the elucidation of the fundamental metal-O2 chemistry occurring in heme-Cu enzymes which effect reductive O-O cleavage of dioxygen to water. In this report, the chemistry of four heme-peroxo-copper [FeIII-(O22-)-CuII]+ complexes (1-4), varying in their ligand architecture, copper-ligand denticity, or both and thus their structures and physical properties are compared in their reactivity toward CO, PPh3, acids, cobaltocene, and phenols. In 1 and 2, the copper(II) ligand is N4-tetradentate, and the peroxo unit is bound side-on to iron(III) and end-on to the copper(II). In contrast, 3 and 4 contain a N3-tridentate copper(II) ligand, and the peroxo unit is bound side-on to both metal ions. CO "displaces" the peroxo ligand from 2-4 to form reduced CO-FeII and CO-CuI species. PPh3 reacts with 3 and 4 displacing the peroxide ligand from copper, forming (porphyrinate)FeIII-superoxide plus CuI-PPh3 species. Complex 2 does not react with PPh3, and surprisingly, 1 reacts neither with PPh3 nor CO, exhibiting remarkable stability toward these reagents. The behavior of 1 and 2 compared to that of 3 and 4 correlates with the different denticity of the copper ligand (tetra vs tridentate). Complexes 1-4 react with HCl releasing H2O2, demonstrating the basic character of the peroxide ligand. Cobaltocene causes the two-electron reduction of 1-4 giving the corresponding micro-oxo [FeIII-(O2-)-CuII]+ complexes, in contrast to the findings for other heme-peroxo-copper species of different design. With t-butyl-substituted phenols, no reaction occurs with 1-4. The results described here emphasize how ligand design and variations influence and control not only the structure and physical properties but also the reactivity patterns for heme-Cu/O2 adducts. Implications for future investigations of protonated heme/Cu-peroxo complexes, low-spin analogues, and ultimately O-O cleavage chemistry are discussed.     

Stability and thermodynamics of La(III)-, Pr(III)-, Nd(III)-, Gd(III)- and Eu(III)-p-nitrobenzaldehyde thiosemicarbazone systems

Three complexes containing bidentate N-2,3-dimethylphenylglycine, (2,3-HDPG), N-2,4-dimethylphenylglycine, (2,4-HDPG) and N-2-ethylphenylglycine, (2-HEPG) acids have been prepared and characterized. These compounds have the general formula Zn(2,3-DPG)₂·2 H₂O, Zn(2,4-DPG)₂ and Zn(2-EPG)₂·2 H₂O, respectively. The structure of the complexes as inferred from their chemistries have been found to be compatible with the infrared spectral data. The thermal behaviour of these complexes has been studied from their TG, DTG and DSC diagrams obtained in a dynamic atmosphere of pure air. Heats of dehydration have been calculated from DSC curves.     

Complexation Studies of Bidentate Heterocyclic N-Donor Ligands with Nd(III) and Am(III)

A new bidentate nitrogen donor complexing agent that combines pyridine and triazole functional groups, 2-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)pyridine (PTMP), has been synthesized. The strength of its complexes with trivalent americium (Am³⁺) and neodymium (Nd³⁺) in anhydrous methanol has been evaluated using spectrophotometric techniques. The purpose of this investigation is to assess this ligand (as representative of a class of similarly structured species) as a possible model compound for the challenging separation of trivalent actinides from lanthanides. This separation, important in the development of advanced nuclear fuel cycles, is best achieved through the agency of multidentate chelating agents containing some number of nitrogen or sulfur donor groups. To evaluate the relative strength of the bidentate complexes, the derived constants are compared to those of the same metal ions with 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2-pyridin-2-yl-1H-benzimidazole (PBIm). At issue is the relative affinity of the triazole moiety for trivalent f element ions. For all ligands, the derived stability constants are higher for Am³⁺ than Nd³⁺. In the case of Am³⁺ complexes with phen and PBIm, the presence of 1:2 (AmL₂) species is indicated. Possible separations are suggested based on the relative stability and stoichiometry of the Am³⁺ and Nd³⁺ complexes. It can be noted that the 1,2,3-triazolyl group imparts a potentially useful selectivity for trivalent actinides (An(III)) over trivalent lanthanides (Ln(III)), though the attainment of higher complex stoichiometries in actinide compared with lanthanide complexes may be an important driver for developing successful separations.     

Solid compounds of Ce(III), Pr(III), Nd(III), and Sm(III) ions with chrysin

New solid amorphous compounds of Ce(III), Pr(III), Nd(III), and Sm(III) with 5,7-dihydroxyflavone (L,chrysin) were obtained. Their composition and some physicochemical properties were studied by elementary analysis, thermogravimetric analysis, magnetic measurements, ¹H NMR, UV/Vis, and infrared spectroscopies. Upon heating, the hydrated compounds [LnL₂(H₂O)₂Cl]·2H₂O decomposed to the oxides. Structure of the compounds was elucidated on the basis of obtained results. It was found that chelation of the metal ion occurs at the 5-hydroxy-4-keto site.     

The influence of ligand conformation on the thermal spin transitions in iron(III) saltrien complexes

We report the syntheses of six new salts of the iron(III) complexes of four hexadentate Schiff bases of the saltrien-type derived from 1,8-diamino-3,6-diazaoctane and 2 equiv. of the appropriate salicylaldehyde derivative. Three of these new compounds undergo gradual spin-transitions centred between 155-204 K in the solid state, that proceed to 35-50% completeness. One of the other compounds remains high-spin on cooling, another is low-spin, while the last undergoes spin-crossover centred above room temperature. This spin-state variability is typical of solid compounds of this type. As an aid to understanding this behaviour, the crystal structures and magnetochemistry of the known spin-crossover salts [Fe(saltrien)]PF6, [Fe(saltrien)]ClO4 and [Fe(saltrien)]BPh4 have also been reexamined. The structural chemistry of all three salts was found to differ significantly from what has been previously reported. Correlation of the crystal structures and magnetic behaviour of the compounds in this and previous work suggests that the disposition of the two ligand phenoxy groups plays an important role in determining whether high-spin [Fe(saltrien)]+ complexes can undergo thermal spin-transitions.     

Neodimium(III) luminescence in the mixed ligand compounds with β-diketones

The luminescent spectral characteristics of neodymium(III) tris- and tetrakis-β-diketonates and β-diketonate acido complexes were investigated. The dependence between the intensity of the luminescence and the composition of the coordination sphere of the complexes was revealed. The most intense luminescence in the IR region possess the neodymium(III) compounds which are the mixed ligand complexes with β-diketones and phosphorus-containing neutral ligands.     

Thermal behaviour and non-isothermal decomposition kinetics of some Nd(III) coordination compounds

The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.     

Sensitized near-infrared lanthanide luminescence from Nd(III)- and Yb(III)-based cyclen-ruthenium coordination conjugates

The development of novel mixed lanthanide-transition-metal (f-d) based supramolecular self-assemblies made from neodymium- and ytterbium-based tetraamide-functionalized cyclen complexes bearing a single 1,10-phenanthroline moiety coordinating to a RuII(bipy)2 (bipy = bipyridine) unit is described. Excitation of the Ru(II) metal-to-ligand charge-transfer band in water gave rise to long-wavelength sensitized emission from the Yb(III) or Nd(III) centers, observed in the near-infrared.     

Studies on mixed ligand complexes of samarium(III), europium(III) and dysprosium(III) with 1-nitroso-2-naphthol and trioctylphosphine oxide

The extraction behavior of Sm(III), Eu(III) and Dy(III) with 1-nitroso-2-naphthol (HA) and trioctylphosphine oxide (TOPO) in methyl isobutyl ketone (MIBK) from aqueous NaClO₄ solutions in the pH range 4–9 at 0.1M ionic strength has been studied. The equilibrium concentrations of Sm and Dy were measured using their short-lived neutron activation products,¹⁵⁵Sm and^165mDy, respectively. In the case of Eu, the concentrations were assayed through the^152,154Eu radiotracer. The distribution ratios of these elements were determined as a function of pH, 1-nitroso-2-naphthol and TOPO concentrations. The extractions of Sm, Eu and Dy were found to be quantitative with MIBK solutions in the pH range 5.9–7.5, 5.6–7.5 and 5.8–7.5, respectively. Quantitative extraction of Eu was also obtained between pH 5.8 and 8.8 with chloroform solutions. The results show that these lanthanides (Ln) are extracted as LnA₃ chelates with 1-nitroso-2-naphthol alone, and in the presence of TOPO as LnA₃(TOPO) and LnA₃(TOPO)₂ adducts. The extraction constants and the adduct formation constants of these complexes have been calculated.     

Non additivity of ligand effects on 59Co NMR chemical shifts in Co(III) complex compounds

⁵⁹Co chemical shift in a number of Co(III) complexes of the type CoA_6-xB_x(x = 0–6, A and B denote corresponding ligators) containing mono- and/or bidentate ligands, was measured. In almost all cases studied it was found that chemical shift appear at lower field than expected on the basis of the Rule on Additivity of Ligand Effects on ⁵⁹Co chemical shift. The non additivity of the ligand effects on ⁵⁹Co chemical shift has been discussed in terms of ligand field theory. It was shown that negative deviations from additivity has to be expected.     

A series of new ternary and quaternary compounds in the Li(I)-Ga(III)-Te(IV)-O system

Systematic explorations of new compounds in the Li(I)-Ga(III)-Te(IV)-O system led to two new isomeric ternary gallium tellurites, namely, α-Ga(2)(TeO(3))(3) and β-Ga(2)(TeO(3))(3), and two new quaternary lithium gallium tellurites, namely, HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) and Li(9)Ga(13)Te(21)O(66). α-Ga(2)(TeO(3))(3) is a noncentrosymmetric structure (I4?3d) and displays a moderately strong second-harmonic-generation response that is comparable with that of KDP (KH(2)PO(4)). Its structure features a condensed three-dimensional (3D) network alternatively connected by GaO(4) tetrahedra and TeO(3) trigonal pyramids via corner sharing. β-Ga(2)(TeO(3))(3) is centrosymmetric (P6(3)/m) and features a 3D open framework composed of Ga(2)O(9) dimers bridged by TeO(3) groups with one-dimensional (1D) 12-MR channels along the c axis. Although both HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) and Li(9)Ga(13)Te(21)O(66) crystallized in the same space group R3?, they belong to different structure types. The structure of HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) can be viewed as the 1D tunnels of the 3D gallium tellurite being occupied by Li(+) and H(+) ions whereas the structure of Li(9)Ga(13)Te(21)O(66) is a complicated 3D framework composed of alternating gallium tellurite layers and GaO(6) octahedral layers with Li(+) cations being located at the cavities of the structure. Optical diffuse-reflectance spectrum measurements indicate that all four compounds are insulators and transparent in the range of 300-2500 nm.     

Studies on synthesis, infrared and fluorescence spectra of new europium (III) and terbium (III) complexes with an beta-diketonate-type ligand

A new beta-diketonate-type ligand, N-(2-amino-6-methyl-pyridinyl)ketoacetamide (L) and its complexes with europium (III) and terbium (III) were synthesized. The complexes were characterized by elemental analysis, infrared spectra and conductivity. The europium (III) and terbium (III)-ions were found to coordinate to the CO oxygen atoms and pyridine nitrogen atoms. The fluorescence properties of these complexes in solid, DMF and CH3OH were studied. The solvent factors influencing the fluorescent intensity are discussed.     

Extraction of Nd(III), Tb(III) and Lu(III) with picrolonic acid in methylisobutylketone

The extraction of Nd(III), Tb(III) and Lu(III) as representatives of lanthanide(III) ions with picrolonic acid (HPA) in methylisobutylketone (MIBK) has been studied from pH 1-2 buffer solutions. The composition of the organic species formed in the organic phase after extraction has been determined by slope analysis to be M(PA)₃ [M = Nd(III), Tb(III) and Lu(III)]. The equilibrium constant values, log k _ex This revised version was published online in July 2006 with corrections to the Cover Date.     

(Chloromethyl)thallium(III) compounds

Aryl(chloromethyl)thallium chlorides, Ar(ClCH₂)TlCl (Ar=C₆H₅, p-CH₃C₆H₄) have been prepared by treatment of arylthallium dichlorides with diazomethane. The derived carboxylates, Ar(ClCH₂)TlX, react with HgX₂ to give the dicarboxylates, (ClCH₂)TlX₂ (X = OCOCH₃, OCOC₃H₇-i) and with tetramethyltin to give CH₃(ClCH₂)TlX compounds. R(ClCH₂)TIX compounds (R = CH₃, C₆H₅, p-CH₃C₆H₄) undergo disproportionation in methanol to R₂TlX and (ClCH₂)₂TlX compounds.     

Thermal phase transitions in antimony (III) oxides

Previous reports of the thermal behaviour of antimony trioxide show significant disagreement on the values for the temperatures associated with specific thermal events. In this reappraisal, samples of both polymorphs of Sb₂O₃ (senarmontite and valentinite) have been analysed using X-ray diffraction and simultaneous differential thermal/thermogravimetric analysis techniques. The senarmontite-valentinite phase transition has been observed to occur as a multi-stage event commencing at temperatures as low as 615±3 °C—evidence of oxidation to Sb₂O₄ under inert atmosphere may indicate that the depression is related to surface- or bulk-bound water. Valentinite produced by mechanical milling of senarmontite exhibits the reverse phase transition to senarmontite at a lower than normal temperature (445±3 °C). Oxidation temperatures of 531±4 °C for senarmontite and 410±3 °C for mechanically derived valentinite were also recorded.