Synthesis and crystal structure of unprecedented oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes

Two new polynuclear oxo/hydroxo-bridged polynuclear gallium(III) aqua complexes are obtained upon treatment of Ga(3+)(aq) with pyridine: the supramolecular compound of macrocyclic cavitand cucurbit[6]uril with gallium complex containing 32 metal atoms [Ga(32)(mu(4)-O)(12)(mu(3)-O)(8)(mu(2)-O)(7)(mu(2)-OH)(39)(H(2)O)(20)](PyH subsetC(36)H(36)N(24)O(12))(3)(NO(3))(6).53H(2)O (1) and the tridecanuclear complex [Ga(13)(mu(3)-OH)(6)(mu(2)-OH)(18)(H(2)O)(24)](NO(3))(15).12H(2)O (2). It follows that two modes of nucleation exist when Ga(3+)(aq) is hydrolyzed: one around the tetrahedral GaO(4) units (complex 1) and the other around the octahedral GaO(6) units (complex 2). This is the first time that polynuclear oxo/hydroxo-bridged aqua complexes of Ga(III) have been isolated without the use of other ligands to control or block olygomerization.     

Quantitative adsorption and local structures of gallium(III) at the water-alpha-FeOOH interface

The adsorption of Ga(III) at the water-alpha-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3-11 and surface coverages of 0.9-3.2 micromol/m2, Ga(III) was found to adsorb strongly to alpha-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)4- than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water-alpha-FeOOH interface, with practically no structural variations as a function of pH or total gallium concentration. Analysis of the first coordination shell required an anharmonic model indicating a distorted geometry of the GaO6 octahedra, with mean Ga-O distances at 1.96-1.98 angstroms. A method based on the continuous Cauchy wavelet transforms (CCWT) was used to identify backscattering atoms in the higher coordination shells. This analysis indicated predominately Fe backscattering, and the quantitative data fitting resulted in three Ga-Fe paths at 3.05, 3.2, and 3.55 angstroms, which correspond to two edge-sharing and one corner-sharing linkage, respectively. The collective results from EXAFS spectroscopy showed that Ga(III) adsorbs to Fe equivalent sites at the surface alpha-FeOOH as an extension of the rows of Fe octahedra in the bulk structure. This interpretation was further corroborated by a Ga-Fe-Fe multiple scattering path at 6.13 angstroms. The quantitative adsorption and proton data were modeled using a surface complexation formalism based on a 1 pK(a) constant capacitance model. In agreement with the EXAFS results, the model obtained included one predominating surface complex with the stoichiometry [triple bond]FeOGa(OH)2(-0.5) and the stability constant log beta(intr.) = -2.55 +/- 0.04 ([triple bond]FeOH(-0.5) + Ga3+ + 2H2O <--> [triple bond]FeOGa(OH)2(-0.5) + 3H+).     

Effect of alkyl substitueras in hydrophobic 8-quinolinol on the extraction of gallium(III) and applications to the separation of gallium(III) from aluminum(III)

The extraction of gallium(III) with newly prepared 5-alkyloxymethyl-8-quinolinol derivatives with alkyl substituent at the 2-position in 8-quinolinol moiety has been studied. The Ga(III)-5-octyloxymethyl-8-quinolinol (HO(8)Q), Ga(III)-2-methyl-5-octyloxymethyl-8-quinolinol (HMO(8)Q), Ga(III)-2-methyl-5-hexyloxymethyl-8-quinolinol (HM-O(6)Q), and Ga(HI)-2-n-butyl-5-hexyloxymethyl-8-quinolinol (HNBO(6)Q) complexes extracted in heptane from a perchloric acid medium were Ga(O(8)Q)(3), Ga(OH)(H(2)O)(MO(8)Q)(2), Ga(OH)(H(2)O)(MO(6)Q)(2) and Ga(OH)H(2)O)(NBO(6)Q)(2), respectively. The 2-tert-butyl-5-hexyloxymethyl-8-quinolinol did not exhibit any reactivity toward gallium(III). The extraction constants for Ga(O(8)Q)(3) (K(ex) = [Ga(O(8)Q)(3)](org) [H(+)](3)/[Ga(3+)][HO(8)Q](org)(3)), Ga(OH)(H(2)O)(MO(8)Q)(2) (K(ex) = [Ga(OH) (H(2)O)(MO(8)Q)(2)](org) [H(+)](3)/[Ga(3+)][HMO(8)Q](org)(2)), Ga(OH)(H(2)O)(2)(MO(6)Q)(2) and Ga(OH)(H(2)O)(NBO(6)Q)(2), which were extracted in heptane from an acidic solution, are 10(3.21 +/- 0.12), 10(-4.24 +/- 0.16), 10(-3.84 +/- 0.16) and 10(-4.07 +/- 0.07), respectively at I = 0.1 M and 25 degrees C. HNBO(6)Q exhibited very high selectivity toward gallium(III) in the presence of aluminum(III). Even in the presence of a 100 fold excess of aluminum(III) to gallium(III) (1.43 x 10(-5) M), gallium(III) was completely extracted and the distribution ratio of aluminum(III) was found to be less than 2.0 x 10(-3).     

Simultaneous determination of gallium(III) and indium(III) by derivative spectrophotometry

A simple, selective and sensitive derivative spectrophotometric method is proposed for the simultaneous determination of gallium(III) and indium(III) in mixtures using 1-(2-pyridylazo)-2-naphthol in cationic micellar medium, without any prior separation. Beer's law is obeyed between 2.80x10(-1)-3.63 and 4.60x10(-1)-9.20 mug ml(-1) concentration of Ga(III) and In(III) at 550 and 542 nm, the isodifferential points of indium and gallium complexes in the first-order derivative mode, respectively. The proposed method is successfully applied for the determination of gallium and indium in standard reference materials and synthetic binary mixtures with a relative error of +/-2.07 and +/-2.55%, respectively.     

Reactions of a gallium(II)-diazabutadiene dimer, [{{[(H)C(Bu(t))N]2}GaI}2], with [ME(SiMe3)2] (M = Li or Na; E = N, P, or As): structural, EPR, and ENDOR characterization of paramagnetic gallium(III) pnictide complexes

The reactions of the paramagnetic gallium(II) complex [{(Bu(t)-DAB)GaI}2] (Bu(t)-DAB = {(Bu(t))NC(H)}2) with the alkali metal pnictides [ME(SiMe3)2] (M = Li or Na; E = N, P, or As) have been carried out under a range of stoichiometries. The 1:2 reactions have led to a series of paramagnetic gallium(III)-pnictide complexes, [(Bu(t)-DAB)Ga{E(SiMe3)2}I] (E = N, P, or As), while two of the 1:4 reactions afforded [(Bu(t)-DAB)Ga{E(SiMe3)2}2] (E = P or As). In contrast, treatment of [{(Bu(t)-DAB)GaI}2] with 4 equiv of [NaN(SiMe3)2] resulted in a novel gallium heterocycle coupling reaction and the formation of the diradical species [(Bu(t)-DAB)Ga{N(SiMe3)2}{[CC(H)N2(Bu(t))2]Ga[N(SiMe3)2]CH3}]. The mechanism of this unusual reaction has been explored, and evidence suggests it involves an intramolecular transmethylation reaction. The X-ray crystal structures of all prepared complexes are reported, and all have been characterized by EPR and ENDOR spectroscopies. The observed spin Hamiltonian parameters provide a detailed picture of the distribution of the unpaired spin density over the molecular frameworks of the complexes.     

Fluorimetric determination of trace amounts of aluminium and gallium with salicylaldehyde-1-phthalazinohydrazone

Fluorimetric determinations of aluminium and gallium, based on the formation of fluorescence complexes between Al(III) or Ga(III) and salicylaldehyde-1-phthalazinohydrazone, SAPhH, are proposed. The Al(III)-SAPhH complex exhibits fluorescence with maximum emission at 475 nm when excited at 414 nm; the Ga(III)-SAPhH chelate has emission and excitation maxima at 480 and 410 nm, respectively. For both determinations the range of application is 10–100 ng/ml. Aluminium has been determined in waters, and gallium in aluminium and nickel alloys.     

Equilibrium study of the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate, 3-mercaptopropionate and 2-mercaptobenzoate

Equilibrium studies were carried out by pH-potentiometry on the systems of aluminium(III), gallium(III) and indium(III) with mercaptoacetate (MerAc^2?), 3-mercaptopropionate (MerPr^2?) and 2-mercaptobenzoate (MerBe^2?). It was found that the complex-forming properties of the Al³⁺ ion towards these mercaptocarboxylic acid ligands differ from those of Ga³⁺ and Al³⁺. Under the conditions of the study, Al³⁺ forms only hydroxo complexes, while Ga³⁺ and In³⁺ form relatively stable complexes involving the simultaneous coordination of the carboxylate and the deprotonated mercapto group. In all cases the equilibrium systems can be described without the assumption of polynuclear complexes. The complexes Ga(MerAc)₂ and Ga(MerBe)₂ show marked stability; this was interpreted in terms of back-coordination and of interaction between the d¹⁰ electrons of the Ga³⁺ ion and the empty d orbitals of the S donor atom. Complexes of composition ML_i are not formed in the Ga³⁺-MerPr^2? system; this points to the importan roles of the number of atoms in the chelate ring and the higher stability of the Ga(III)-hydroxo complexes.     

Oxidation reactions of an anionic gallium(I) N-heterocyclic carbene analogue with group 16 compounds

The reactivity of an anionic gallium(I) heterocycle, [K(tmeda)][:Ga([N(Ar)C(H)]2)], Ar = C6H3Pr(i)2-2,6, towards sources of elemental chalcogens and diorgano-dichalcogenides has been investigated and comparisons drawn with the reactivity of the valence isoelectronic N-heterocyclic carbene class of ligand. The reactions of the heterocycle with N2O or (Te)PEt3 yielded the dimeric, dianionic gallium(III) complexes, [K(L)]2[(mu-E)Ga([N(Ar)C(H)]2)]2, E = O, L = tmeda; E = Te, L = THF. Treatment of [K(tmeda)][:Ga([N(Ar)C(H)]2)] with the diphenyl dichalcogenides, PhEEPh, E = Se or Te, gave the one dimensional polymer, [K[(PhSe)2Ga([N(Ar)C(H)]2)]]infinity and the monomeric complex, [K(OEt2)3][(PhTe)2Ga([N(Ar)C(H)]2)], respectively. The X-ray crystal structures of the four complexes are reported.     

A redox series of gallium(III) complexes: ligand-based two-electron oxidation affords a gallium-thiolate complex

We have prepared a series of gallium(III) complexes of the redox active iminopyridine ligand (IP). Reaction of GaCl(3) with iminopyridine ligand (IP) in the presence of either two or four equivalents of sodium metal resulted in the formation of deep green (IP(-))(2)GaCl (1), or deep purple [(DME)(3)Na][(IP(2-))(2)Ga] (2a), respectively. Complex 1 is paramagnetic with a room temperature magnetic moment of 2.3 μ(B) which falls to 0.5 μ(B) at 5 K. These observations indicate that two ligand radicals comprise a triplet at room temperature which becomes a singlet due to antiferromagnetic coupling at low temperature. Complex 2 is diamagnetic. Cyclic voltammograms recorded on 0.3 M Bu(4)NPF(6) THF solutions of [Na(THF)(6)][(IP(2-))(2)Ga](-) (2b) indicate that oxidation of 2b occurs in two two-electron steps at -1.31 V and -0.54 V vs. SCE. The observation of two-electron redox events indicates that electronic coupling through the gallium(III) center is minimal and that the two IP ligand on 2b are oxidized concurrently. Oxidation of 2 with one equivalent of MeS-SMe afforded the two-electron oxidized product (IP(-))(2)Ga(SMe) (3). This complex has an electronic structure analogous to 1. Accordingly, both 1 and 3 are deep green in color and magnetic susceptibility measurements performed on 3 confirm the triplet character of the complex at room temperature. Electron paramagnetic resonance experiments on 1 and 3 display a quartet signal at g = 2.0 which confirmed the triplet nature of the compounds, and a half field signal consistent with the integer spin state.     

Bis(allyl)gallium cation, tris(allyl)gallium, and tetrakis(allyl)gallate: synthesis, characterization, and reactivity

A series of cationic, neutral, and anionic allylgallium complexes has been isolated and fully characterized. It includes neutral [Ga(η(1)-C(3)H(5))(3)(L)] (1, L = THF; 2, L = OPPh(3)), cationic [Ga(η(1)-C(3)H(5))(2)(THF)(2)](+)[A](-) (3, [A](-) = [B(C(6)F(5))(4)](-); 4, [A](-) = [B(C(6)H(3)Cl(2))(4)](-)), as well as anionic [Cat](+)[Ga(η(1)-C(3)H(5))(4)](-) (5, [Cat](+) = K(+); 6, [Cat](+) = [K(dibenzo-18-c-6](+); 7, [Cat](+) = [PPh(4)](+)). Binding modes of the allyl ligand in solution and in the solid state have been studied comparatively. Single crystal X-ray analyses revealed a four-coordinate neutral gallium center in 2, a five-coordinate cationic gallium center in 4 and [4·THF], and a four-coordinate anionic gallium center with a bridging μ(2)-η(1):η(2) coordination mode of the allyl ligand in 6. The reactivity of this series of allylgallium complexes toward benzophenone and N-heteroaromatics has been investigated. Counterion effects have also been studied. Reactions of 1 and 5 with isoquinoline revealed the first examples of organogallium complexes reacting under 1,2-insertion with pyridine derivatives.     

A macrocyclic ligand able to bind gallium(III) by preorganized pendant arms; coordination and kinetic studies

The equilibria and kinetics of the binding of gallium(III) to 4-(N),10-(N)-bis[2-(3-hydroxo-2-oxo-2-H-pyridine-1-y1)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) were investigated in acidic medium at ionic strength 1 M (NaClO4). Spectrophotometric titrations in the UV region revealed that L is able to bind Ga3+ also at high H+ concentration. The kinetic (stopped-flow) experiments are interpreted on the basis of three parallel reaction paths (i) M3+ + H2L2+ = M(H2L)5+ where M(H2L)5+ is in a steady state, (ii) M(OH)2+ + H2L2+ = M(HL)4+ + H2O and (iii) M(OH)2+ + HL+ = ML3+ + H2O. The first-order rate constants for conversion of the outer-sphere into the inner-sphere complexes are similar to those of the Ga(III)/tropolone system which is known to react according to the dissociative Id mechanism and to the relevant rate constants for water exchange at the metal ion. The effects of pH on the UV-Vis absorption, fluorescence emission properties and NMR spectral features on the Ga(III)/L system were also investigated. Spectrophotometric titrations in the UV region reveal that, in acid medium the prevailing species is M(HL)4+ whereas the chelate ML3+ prevails for [H+] < 0.01 M. The results indicate metal coordination at the oxygen atoms of the 3-hydroxo-2-oxopyridine residues.     

Electron transfer. 147. Reductions with gallium(I)

Solutions 0.03-0.05 M in gallium(I) can be generated by treatment of the "mixed" halide Ga(I)Ga(III)Cl(4) with cold water under argon and then removing the precipitated metallic gallium and Ga(OH)(3) by centrifugation. Ga(I) is lost from such preparations with a half-life of about 3 h at 0 degrees C. These solutions, which may be handled by conventional techniques, readily reduce I(3)(-), IrCl(6)(2)(-), Fe(bipy)(3)(3+), Fe(NCS)(2+), aquacob(III)alamin, and a group of ring-substituted derivatives of Ru(NH(3))(5)(py)(3+) but are inert to (NH(3))(5)CoCl(2+) and (NH(3))(5)CoBr(2+). All reactions give Ga(III). Reduction of HCrO(4)(-) in 2-ethyl-2-hydroxybutanoate buffers (pH 3.6) yields a Cr(IV) chelate of the buffering anion but forms Cr(III) when carried out in 0.01 M H(+). Reactions of le(-) oxidants proceed via successive single changes with the conversion Ga(II) --> Ga(III) much more rapid than Ga(I) --> Ga(II). Only for the reactions of I(3)(-) and Fe(NCS)(2+) is there evidence for redox bridging.     

Fluorimetric determination of gallium in a nickel alloy and aluminium with N-oxalylamine(salicylaldehyde hydrazone)

A fluorimetric determination of gallium, based on the formation of the fluorescent chelate with N-oxalylamine(salicylaldehyde hydrazone) (OSH)-Ga(III), is proposed. The complex has excitation and emission maxima at 395 and 475 nm, respectively. The detection limit is 3 ng/ml and Ga can be determined up to 277 ng/ml. The method has been applied to the determination of gallium in a nickel alloy and aluminium. Extraction with n-butyl acetate from 6M hydrochloric acid medium has been used to separate Ga from the interfering elements in the alloys.     

Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: synthetic, structural and theoretical studies

The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar'2E=EAr'2, E = Ge, Sn or Pb, Ar' = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar'2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar'Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies.     

Extractive recovery of gallium(III) from acid sulfate solutions with primary amines

Liquid extraction of Ga(III) ions with technical-grade aliphatic amines from sulfate media at a temperature of 20 ± 5°C was studied. The composition of the complex being extracted was determined and the equation of the reaction of Ga(III) extraction with primary amines was derived. The equilibrium constant of the reaction of gallium(III) extraction from acid sulfate solutions was found.     

Trialkylphosphine-stabilized copper(I) gallium(III) phenylchalcogenolate complexes: crystal structures and generation of ternary semiconductors by thermolysis

A series of organometallic trialkylphosphine-stabilized copper gallium phenylchalcogenolate complexes [(R(3)P)(m)Cu(n)Me(2-x)Ga(EPh)(n+x+1)] (R = Me, Et, (i)Pr, (t)Bu; E = S, Se, Te; x = 0, 1) has been prepared and structurally characterized by X-ray diffraction. From their molecular structures three groups of compounds can be distinguished: ionic compounds, ring systems, and cage structures. All these complexes contain one gallium atom bound to one or two methyl groups, whereas the number of copper atoms, and therefore the nuclearity of the complexes, is variable and depends mainly on size and amount of phosphine ligand used in synthesis. The Ga-E bonds are relatively rigid, in contrast to flexible Cu-E bonds. The lengths of the latter are controlled by the coordination number and steric influences. The Ga-E bond lengths depend systematically on the number of methyl groups bound to the gallium atom, with somewhat shorter bonds in monomethyl compounds compared to dimethyl compounds. Quantum chemical computations reproduce this trend and show furthermore that the rotation of one phenyl group around the Ga-E bond is a low energy process with two distinct minima, corresponding to two different conformations found experimentally. Mixtures of different types of chalcogen atoms on molecular scale are possible, and then ligand exchange reactions in solution lead to mixed site occupation. In thermogravimetric studies the complexes were converted into the ternary semiconductors CuGaE(2). The thermolysis reaction is completed at temperatures between 250 and 400 °C, typically with lower temperatures for the heavier chalcogens. Because of significant release of Me(3)Ga during the thermolysis process, and especially in case of copper excess in the precursor complexes, binary copper chalcogenides are obtained as additional thermolysis products. Quaternary semiconductors can be obtained from mixed chalcogen precursors.     

(Cyclophan-Metall)-Komplexe: Synthese und Kristallstruktur von ([3.3]Paracyclophan)gallium(I)-tetrabromgallat(III)

Cyclophane-Metal Complexes: Synthesis and Crystal Structure of ([3.3]Paracyclophane)gallium(I) Tetrabromogallate(III) [3.3]Paracyclophane forms 1:1 complexes 2a and 2b with both Ga[GaCl₄] and Ga[GaBr₄]. The crystalline products obtained from toluene solution at room temperature are much less sensitive to air and moisture than most other arene complexes of Ga(I). Solubilities in standard organic solvents are very low, suggesting coordination polymers. The X-ray diffraction analysis of 2b confirms the presence of a two-dimensional network. Both aromatic rings of each cyclophane molecule are η⁶-coordinated from the outer side to Ga(I)-atoms. The position of these metal cations is 2.75 Å above the ring centres. The arene rings are parallel within each cyclophane, but tilted by 48.5° with respect to those of the neighbouring cyclophane. The coordination sphere of the Ga(I) centres is completed by two Br-atoms of two GaBr anions, which link the Ga(I) cations to give … Ga[GaBr₄] Ga[GaBr₄]Ga … strands. The double interconnection of the Ga(I)-atoms gives rise to a two-dimensional sheet structure, which is thus different from the structure of the previously described Ga[GaBr₄] complex of [2.2]paracyclophane, where a three-dimensional network was observed.     

Chalcone-derived thiosemicarbazones and their zinc(II) and gallium(III) complexes: spectral studies and antimicrobial activity

Chalcone-derived 3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCTPh) (1), 3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4ClPh) (2), 3-(4-bromophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4BrPh) (3), and 3-(4-nitrophenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4NO₂Ph) (4) were obtained as well as their gallium(III) and zinc(II) complexes [Ga(PyCTPh)₂]NO₃ (Ga1), [Ga(PyCT4ClPh)₂]NO₃ (Ga2), [Ga(PyCT4BrPh)₂]NO₃ (Ga3), [Ga(PyCT4NO₂Ph)₂]NO₃ (Ga4), [Zn(PyCTPh)₂] (Zn1), [Zn(PyCT4ClPh)₂] (Zn2), [Zn(PyCT4BrPh)₂] (Zn3), and [Zn(PyCT4NO₂Ph)₂] (Zn4). The chalcones, thiosemicarbazones, and zinc(II) complexes were not active against Pseudomonas aeruginosa. The thiosemicarbazones proved to be more active than the parent chalcones against Staphylococcus aureus and Candida albicans. Coordination to zinc(II) resulted in activity improvement of most thiosemicarbazones against S. aureus. Coordination to gallium(III) significantly improved the antimicrobial activity of all thiosemicarbazones against the studied micro-organisms, suggesting this to be an effective strategy for antimicrobial activity enhancement.     

Sorption of microamounts of gallium(III) on Fe(OH)3 and Fe2O3 precipitates

Summary The sorption of microamounts of gallium(III) on Fe(OH)₃ and Fe₂O₃ precipitates was studied by using⁶⁷Ga as radioactive indicator. The dependence of sorption of microamounts of gallium(III) on pH, sorbent concentration, and duration of the contact between gallium-(III) and Fe(OH)₃ precipitate, was established. In the presence of sodium citrate the sorption of microamounts of gallium (III) on Fe₂O₃ markedly decreased. Iron(III) hydroxide and Fe₂O₃ precipitates are suitable collectors for the preconcentration of gallium (III) traces in solution.

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Zusammenfassung Die Adsorption von Mikromengen Ga(III) an Niederschlägen von Fe(OH)₃ und Fe₂O₃ wurde mit Hilfe von⁶⁷Ga als radioaktivem Indikator untersucht. Die Abhängigkeit der Adsorption vom pH, von der Konzentration des Sorptionsmittels und von der Dauer des Kontakts zwischen Ga(III) und Fe(0H)₃ wurde festgestellt. In Gegenwart von Na-Citrat wird die Sorption an Fe₂O₃ merklich geringer. Eisen (III)hydroxid- und Fe₂O₃-Niederschläge eignen sich als Kollektoren zur Anreicherung von Ga(III)-Spuren in einer Lösung.

     

Phenylthiyl radical complexes of gallium(III), iron(III), and cobalt(III) and comparison with their phenoxyl analogues.

Three hexadentate, asymmetric pendent arm macrocycles containing a 1,4,7-triazacyclononane-1,4-diacetate backbone and a third, N-bound phenolate or thiophenolate arm have been synthesized. In [L(1)](3)(-) the third arm is 3,5-di-tert-butyl-2-hydroxybenzyl, in [L(2)](3)(-) it is 2-mercaptobenzyl, and in [L(3)](3)(-) it is 3,5-di-tert-butyl-2-mercaptobenzyl. With trivalent metal ions these ligands form very stable neutral mononuclear complexes [M(III)L(1)] (M = Ga, Fe, Co), [M(III)L(2)] (M = Ga, Fe, Co), and [M(III)L(3)] (M = Ga, Co) where the gallium and cobalt complexes possess an S = 0 and the iron complexes an S = (5)/(2) ground state. Complexes [CoL(1)].CH(3)OH.1.5H(2)O, [CoL(3)].1.17H(2)O, [FeL(1)].H(2)O, and [FeL(2)] have been characterized by X-ray crystallography. Cyclic voltammetry shows that all three [M(III)L(1)] complexes undergo a reversible, ligand-based, one-electron oxidation generating the monocations [M(III)L(1)(*)](+) which contain a coordinated phenoxyl radical as was unambiguously established by their electronic absorption, EPR, and M?ssbauer spectra. In contrast, [M(III)L(2)] complexes in CH(3)CN solution undergo an irreversible one-electron oxidation where the putative thiyl radical monocationic intermediates dimerize with S-S bond formation yielding dinuclear disulfide species [M(III)L(2)-L(2)M(III)](2+). [GaL(3)] behaves similarly despite the steric bulk of two tertiary butyl groups at the 3,5-positions of the thiophenolate, but [Co(III)L(3)] in CH(2)Cl(2) at -20 to -61 degrees C displays a reversible one-electron oxidation yielding a relatively stable monocation [Co(III)L(3)(*)](+). Its electronic spectrum displays intense transitions in the visible at 509 nm (epsilon = 2.6 x 10(3) M(-)(1) cm(-)(1)) and 670sh, 784 (1.03 x 10(3)) typical of a phenylthiyl radical. The EPR spectrum of this species at 90 K proves the thiyl radical to be coordinated to a diamagnetic cobalt(III) ion (g(iso) = 2.0226; A(iso)((59)Co) = 10.7 G).