Tetravalent Metal Ions Research Articles

Design, formation and properties of tetrahedral M(4)L(4) and M(4)L(6) supramolecular clusters.

The rigid tris- and bis(catecholamide) ligands H(6)A, H(4)B and H(4)C form tetrahedral clusters of the type M(4)L(4) and M(4)L(6) through self-assembly reactions with tri- and tetravalent metal ions such as Ga(III), Fe(III), Ti(IV) and Sn(IV). General design principles for the synthesis of such clusters are presented with an emphasis on geometric requirements and kinetic and thermodynamic considerations. The solution and solid-state characterization of these complexes is presented, and their dynamic solution behavior is described. The tris-catecholamide H(6)A forms M(4)L(4) tetrahedra with Ga(III), Ti(IV), and Sn(IV); (Et(3)N)(8)[Ti(4)A(4)] crystallizes in R3(-)c (No. 167), with a = 22.6143(5) A, c = 106.038(2) A. The cluster is a racemic mixture of homoconfigurational tetrahedra (all Delta or all Lambda at the metal centers within a given cluster). Though the synthetic procedure for synthesis of the cluster is markedly metal-dependent, extensive electrospray mass spectrometry investigations show that the M(4)A(4) (M = Ga(III), Ti(IV), and Sn(IV)) clusters are remarkably stable once formed. Two approaches are presented for the formation of M(4)L(6) tetrahedral clusters. Of the bis(catecholamide) ligands, H(4)B forms an M(4)L(6) tetrahedron (M = Ga(III)) based on an "edge-on" design, while H(4)C forms an M(4)L(6) tetrahedron (M = Ga(III), Fe(III)) based on a "face-on" strategy. K(5)[Et(4)N](7)[Fe(4)C(6)] crystallizes in I43(-)d (No. 220) with a = 43.706(8) A. This M(4)L(6) tetrahedral cluster is also a racemic mixture of homoconfigurational tetrahedra and has a cavity large enough to encapsulate a molecule of Et(4)N(+). This host-guest interaction is maintained in solution as revealed by NMR investigations of the Ga(III) complex.

Complexes of poly(acrylic acid) with some divalent, trivalent and tetravalent metal ions

The formation of metal complexes between poly(acrylic acid) and divalent, trivalent and tetravalent metal ions was studied. For divalent and pseudodivalent metal ions, the stability constants determined according to the method of Gregor et al. [J. Phy. Chem. 59 (1954) 34] are in the order Cu 2+>VO 2+>Co 2+>Ni 2+, Zn 2+. The values were nearly insensitive to the ligand to metal concentration ratio in the range R=1–10. Trivalent and tetravalent ions also induced a strong decrease of the pH but stability constants could not be determined from the formation curves. The metal ions were divided in four groups depending on the shape of the curve ΔpH vs α. These groups differ from one another by (i) the speed of water exchange or (ii) by the speed of ligand exchange in the coordination sphere of the metal in the case of lanthanide's.

Separation of carrier-free 90Y from high level waste by supported liquid membrane using KSM-17

A generator system has been developed for the preparation of carrier-free 90Y from 90Sr present in the high level waste (HLW) of the Purex process by employing a supported liquid membrane (SLM) using 2-ethylhexyl-2-ethylhexyl phosphonic acid (KSM-17 equivalent to PC 88A) supported on a polytetrafluoro ethylene (PTFE) membrane. When uranium depleted Purex HLW at appropriate acidity is passed sequentially through octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) sorbed on chromosorb-102 (abbreviated as CAC) and Zeolite AR1 (synthetic mordenite) columns, all the trivalent, tetravalent and hexavalent metal ions and monovalent 137Cs ions are sorbed. After adjusting to pH 2 with NaOH the resulting effluent is used as feed in a single stage membrane cell partitioned with a PTFE membrane impregnated with KSM-17 and having a feed and receiver compartment with 5.0 ml capacity each. The receiver compartment was filled with a 0.5M HNO3 or 0.5M HCl stripping solution. 90Y alone is preferentially transported across the membrane leaving behind all the impurities viz. 90Sr, 125Sb, 106Ru, 106Rh, etc. in the feed compartment. This technique can yield 90Y in mCi levels in a pure and carrier-free form for medical applications. The feed can be reused repeatedly after allowing for 90Y buildup.

Concentration effects during the formation of poly (acrylic acid)-metal complexes in aqueous solutions

The formation of metal complexes between poly (acrylic acid) and divalent, trivalent and tetravalent metal ions was studied. For divalent metal ions, the formation constants determined according to the method of Gregor et al. strongly decrease with increasing ligand concentration in the range 25–280 mM but are nearly insensitive to the ligand to metal concentration ratio. The metal ions were divided in four groups depending on their effect on the pH decrease of the solution. These groups differ from one another by i) the speed of water exchange or ii) by the speed of ligand exchange in the coordination sphere of the metal. The increase of the ligand concentration or of the ligand to metal ratio always led to an increase of the exchange speed of both water and carboxyl groups.

Preparation and Viscoelastic Behavior of Methacrylate Ionomers Crosslinked by Titanium (IV) and Zirconium (IV)

Ionomers of poly(methyl methacrylate-co-methacrylic acid) crosslinked by titanium (IV) (Ti4+) and zirconium (IV) (Zr4+) ions were prepared, and their structures, optical absorption and viscoelastic properties were investigated. IR measurement revealed that tetravalent metal ions were coordinated by -COO- groups of deprotonated methacrylic acid and functioned as crosslinkers. The coordination of -COO- to the Ti4+ especially brought about strong UV absorption below 360-370 nm owing to charge transfer. Dynamic mechanical thermal analysis (DMTA) showed storage modulus (E′) below glass transition temperature (Tg) and a peak temperature of tan δ for every ionomer not to increase regardless of metal ion content. This was attributed to residual alcohols. E′ above Tg increased with metal ions content, and DMTA for every ionomer was measured up to 350°C. Crosslinking by tetravalent metal ions thus greatly improves heat resistance of host polymers.

Adsorption of Tetravalent Metal Ions to Chelating Resins Containing Iminodiacetic Acid Groups

Abstract With respect to the selectivities, the compositions of species formed by the adsorption of tetravalent metal ions (M4+) to chelating resins containing iminodiacetic acid groups (-LH2) were estimated from the shapes of the adsorption curves and the infrared absorption spectra of the polymer complexes: [-LM(OH)2] for Zr4+ and Hf4+, while [(-LH)4M], [(-L)(-LH)2M], and [(-L)2M] for Th4+.

On the Hydrolysis of Tetravalent Metal Ions

ABSTRACTThe stability constants of the hydroxide complexes of zirconium(IV) and uranium(IV) have been measured at 15, 25 and 35°C [in 1.0 mol dm−3 (Na, H)ClO4] using potentiometry. For zirconium(IV), the results indicate the presence of Zr(OH)3+ and the polymeric species Zr3(OH)48+ and Zr4(OH)88+ whereas the results for uranium(IV) indicate the presence of U(OH)3+ and the polymeric species U4(OH)124+. The hydrolysis of both metal ions was studied at three temperatures allowing the determination of ΔH° and ΔS° of reaction for each species. The results were compared with previous results determined for thorium(IV) under the same experimental conditions to ascertain whether thorium should be used as an analogue for other tetravalent metal ions in safety assessment studies of nuclear repositories.

Point Defect Energies for Strontium Titanate: A Pair-Potentials Study

A crystal potential has been derived for strontium titanate and used to calculate the intrinsic defect properties of the room temperature cubic phase. Interactive potentials for a number of uni-, di-, tri-, and tetra-valent metal ions with O2−, Sr2+, and Ti4+has been derived by well-tried methods, using HFSCF calculations of the ionic charge densities and the conserved density approximation. Kinetic energy, exchange, and correlation contributions to the total interaction energy are approximated by the corresponding contributions to an electron gas of the same charge density as the sum of the two SCF ionic charge densities at each separationR. These impurity×host lattice potentials are then used to calculate the solubility of these ions in cubic SrTiO3as well as the possible mobility of these substituents.

Organic/Inorganic Langmuir−Blodgett Films Based on Metal Phosphonates. 3. An Azobenzene-Derivatized Phosphonic Acid Forms Continuous Lattice Layers with Divalent, Trivalent, and Tetravalent Metal Ions1

Metal phosphonate Langmuir−Blodgett (LB) films of an azobenzene-functionalized phosphonic acid amphiphile, (4-(4‘-tetradecyloxyphenyldiazenyl)phenyl)butylphosphonic acid (A4), have been prepared with Zr4+, La3+, Gd3+, Ba2+, Mn2+, and Cd2+. Film formation and quality are characterized with optical spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The azobenzene chromophores are strongly H-aggregated in all of the metal phosphonate LB films. With divalent and trivalent ions, the in-plane metal phosphonate structure observed in the LB films is the same as that found in analogous solid-state layered phosphonates and depends on the identity of the metal ion. Films of A4 with the lanthanide ions La3+ and Gd3+ form with stoichiometry MH(O3PR)2. When Ba2+ is incorporated into the films, the M(HO3PR)2 structure-type is adopted, while Mn2+ and Cd2+ give rise to films of A4 with the stoichiometry M(O3PR)...

Dipyridyl Amide-Functionalized Polymers Prepared by Ring-Opening-Metathesis Polymerization (ROMP) for the Selective Extraction of Mercury and Palladium

Ring-opening-metathesis polymerization (ROMP) was used for the preparation of a dipyridylcarbamide-functionalized polymer suitable for solid-phase extraction of metal ions from aqueous solutions. Resins were prepared by the copolymerization of the functional monomer N,N-di-2-pyridyl-endo-norborn-2-ene-5-carboxamide (I) with 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene (II), using the well-defined Schrock catalyst Mo(N-2,6-i-Pr2C6H3)CHCMe2Ph(OCMe(CF3)2)2 (III). The polymerization proceeds in a living manner, allowing the stoichiometric buildup of polymers. NMR investigations proved the expected backbone structure of the resulting polymers, where the binding site of the monomer remains unaffected in course of the polymerization. The new materials were investigated in terms of their complexation behavior versus a large variety of mono-, di-, tri-, and tetravalent metal ions employing UV−vis spectroscopy as well as AAS and ICP−OES techniques. The polymer-bound dipyridylamide ligand showed exc...

12-B heteropolyanions as ligands: Synthesis, spectral characterisation and solution studies of [MnIVThMo12O42]4−, [MnIVUMo12O42]4− and [VIVCeMo12O42]4−

Interaction of 12-B heteropolyanions, [XMo12O42]8−, whereX=Ce, Th and U, with tetravalent transition metal ions MnIV and VIV results in the formation of three well defined complexes, viz., (NH4)4[MnIVThMo12O42]·10H2O (I), (NH4)4[MnIVUMo12O42]·8H2O (II) and (NH4)4[VIVCeMo12O42]·8H2O (III), which are characterised by IR, Raman and EPR spectroscopies. Negative shift in the stretching frequency of Mo-Ot bond in IR spectra and appearance of a strong band at 818 cm−1 in Raman spectra support the formation of these complexes. EPR spectra of complexes (I) and (II) show a predominant signal atg=4 and a weak signal atg=2 (with hyperfine coupling from55Mn), characteristic of d3 system, (S=3/2 andI=5/2) with large zero field splitting, showing distortion from octahedral symmetry. EPR parameters of the vanadium complex (III) show thed-electron to be more localised on vanadium(IV) supporting the formulation of vanadium not to be a part of the “Mo12” unit. The oxidising property of complexes (I) and (II) is studied using glucose as the substrate.

MAGNETIC BEHAVIOUR OF LiMg FERRITES WITH TETRAVALENT SUBSTITUENTS

Magnetic ceramics belonging to lithiun ferrite and magnesium ferrite inherently possess rectangular hysteresis loop and have found extensive use in microwave components. Molecular engineering of the ferrite composition and employment of appropriate process parameters are exploited to tailor the material properties for specific needs. Substitution of various tetravalent metal ions in combination with divalent magnesium have been attempted in lithium ferrite. Inclusion of germanium and titanium up to 0.5 ions/FU and tin up to 0.2 ions/FU yielded single phase spinels while with silicon a ferrite-glass composite was formed. Compositions with zirconium resulted in multiphase materials. The different magnetic properties of technical importance for their utility in components have been investigated and the observed behaviour is discussed on the basis of site occupation of the metal ions in the crystal structure and accompanying microstructural developments.

Phenoxyl Radical Complexes of Gallium, Scandium, Iron and Manganese

The hexadentate macrocyclic ligands 1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (L CH 3H3 ), 1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (L(Bu) H3 ) and 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane (L OCH 3-H3 ) form very stable octahedral neutral complexes LM(III) with trivalent (or tetravalent) metal ions (Ga(III) , Sc(III) , Fe(III) , Mn(III) , Mn(IV) ). The following complexes have been synthesized: [L(Bu) M], where M = Ga (1), Sc (2), Fe (3); [L(Bu) Mn(IV) ]PF6 (4'); [L OCH 3M], where M = Ga (1 a), Sc (2 a), Fe (3 a); [L OCH 3Mn(IV) ]PF6 (4 a'); [L CH 3M], where M = Sc (2 b), Fe (3 b), Mn(III) (4 b); [L CH 3Mn(IV) ]2 (ClO4 )3 (H3 O)(H2 O)3 (4 b'). An electrochemical study has shown that complexes 1, 2, 3, 1 a, 2 a and 3 a each display three reversible, ligand-centred, one-electron oxidation steps. The salts [L OCH 3Fe(III) ]ClO4 and [L OCH 3Ga(III) ]ClO4 , have been isolated as stable crystalline materials. Electronic and EPR spectra prove that these oxidations produce species containing one, two or three coordinated phenoxyl radicals. The Mössbauer spectra of 3 a and [3 a](+) show conclusively that both compounds contain high-spin iron(III) central ions. Temperature-dependent magnetic susceptibility measurements reveal that 3 a has an S = 5/2 and [3a](+) an S = 2 ground state. The latter is attained through intramolecular antiferromagnetic exchange coupling between a high-spin iron(III) (S1 = 5/2) and a phenoxyl radical (S2 = 1/2) (H = - 2JS1 S2 ; J = - 80 cm(-1) ). The manganese complexes undergo metal- and ligand-centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxyl radical Mn(IV) complex [Mn(IV) L OCH 3](2+) is accessible.

Complexes With Biologically Active Ligands. Part 1. Synthesis ofCoordination Compounds of Diazoxide With Transition‐ andMain‐Group Cations

Complexes of diazoxide (3-methyl-7-chloro-1,2,4-benzothiadiazine-1,1-dioxide) - an antihypertensive and hyperglycemic pharmacological agent - with a series of transition- and main-group di-, triand tetravalent metal ions were prepared and characterized by elemental analysis, spectroscopic, thermogravimetric, magnetic and conductimetric measurements. The complexes were tested as inhibitors of the enzyme carbonic anhydrase (CA), proving modest activity towards CA II and better inhibition of CA I.

The effect of electrostatic potentials on lithium insertion for perovskite oxides

Lithium was electrochemically inserted into perovskite oxides, SrVO 3 − δ, La 2 3 TiO 3 − δ and (La, Li)TiO 3 − δ, by using a galvanic cell: Li ¦1M LiClO 4 in PC ¦perovskite oxide. The tetravalent transition metal ion (Ti, V) can be reduced to the minimum valence of 3 by lithium insertion. This fact was explained by the effect of valence on the lattice self-potential and site-potential in the ideal perovskite oxide ABO 3. We tried to explain the lithium insertion and high lithium conductivity in the perovskite oxide from the view point of electrostatic potentials.

Structural Features of Organic Reagents Suitable for Spectrophotometric or Fluorometric Determination of Fluoride Based on Mixed-Ligand Complex Formation

Complexes of tetravalent metal ions with chromogenic chelating reagents having only one methyliminodiacetate group ortho to OH group were examined for spectrophotometric or fluorometric determination of fluoride. Zirconium(IV) and hafnium(IV) were superior to thorium(IV) as a central metal ion. Three triphenylmethane dyes showed comparable sensitivities. Although two azo dyes had lower blank values and higher sensitivities than triphenylmethane dyes, further modification involving enhancement of solubilities is required for practical use. Zirconium(IV) complex of a new fluorescent reagent derived from sulfonefluorescein showed an increase in fluorescence intensity on the reaction with fluoride. The mechanism of this change in spectroscopic properties is discussed.

Structure of the blue forms of bisphthalocyanines of rare-earth elements

Using electron spectroscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy, the blue forms of bisphthalocyanines of rare-earth elements were found to have structures of sandwich-type complexes with isoelectronic phthalocyanine ligands linked with tetravalent metal ions, [Pc2−Ln4+Pc2−]0. A comparative spectral and electrochemical study of the blue and green forms oftert-butyl-substituted bisphthalocyanines was carried out for almost the whole series of rare-earth metals. Lutetium octa(perfluoro-tert-butyl)- and perchlorobisphthalocyanines were synthesized for the first time.

Determination of fluoride in the presence of tetravalent metal ions with an ion-selective electrode: application to raw materials of fluoride glasses

The performance of masking reagents, viz., ethylenediamine-N,N,N′,N′-tetraacetic acid, trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid, diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) and triethylenetetramine-N,N,N′,N″,N″′,N″′-hexaacetic acid(TTHA), was studied for the determination of fluoride in the presence of HfIV and ThIV using an ion-selective electrode. Hafnium(IV) was effectively masked using an excess of DTPA at pH 6. TTHA was the best reagent for masking ThIV, while DTPA provided an alternative for fluoride concentrations of <1 × 10–5 mol dm–3. The masking reaction was rapid and contamination from membrane-dissolution was negligible. Fluoride contents in raw materials of fluoride glasses, viz., ZrF4, HfF4, and ThF4, were determined.

Neutron inelastic scattering studies of UF4 and NpF4

Neutron inelastic scattering experiments have been performed on UF4 and NpF4. We had anticipated observing a number of sharp magnetic transitions in these experiments because the tetravalent metal ions are expected to have localized f states. However, very few transitions were observed, three and two in UF4 and NpF4, respectively. Except for the lowest-lying level (at 1.5 meV) in UF4 the transitions are wider than the instrumental resolution, suggesting a strong interaction between the electronic states and lattice vibrations. The levels observed do not correspond to those predicted by a crystal-field scheme recently proposed from optical spectroscopy. However, the paucity of observed levels in our experiments excludes us proposing an alternative scheme. The 1.5 meV energy level in UF4 is in good agreement with that deduced from specific heat and magnetic susceptibility data.

Electronic structure and chemical bonding in Ba-Cu-O layer systems

The cluster method of discrete variation was used to study compounds containing chains of plane-coordinated copper ions separating oxygen-copper planes. We also examined real YBa2Cu3O7 and hypothetical MBa3Cu4O9 systems (M is a tetravalent metal ion). A study was carried out on the transformation of the valence band and structure of the molecular orbitals in the Fermi level in going from YBa2Cu3O7 to MBa3Cu4O9. The chemical bonding was analyzed and the role of the “interchain” interaction in the bonding of the copper and oxygen atoms in different crystallographic positions was determined.