Takaharu Honjo

USE OF 1-ALKYL-3-METHYLIMIDAZOLIUM HEXAFLUOROPHOSPHATE ROOM TEMPERATURE IONIC LIQUIDS AS CHELATE EXTRACTION SOLVENT WITH 4,4,4-TRIFLUORO-1-(2-THIENYL)-1,3-BUTANEDIONE

Possible use of room temperature ionic liquids (RTILs) as chelate extraction solvent was evaluated by using 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF(6)]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF(6)]). These RTILs showed high extraction performance for divalent metal cations with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta). The extracted metals were back-extracted into 1moldm(-3) nitric acid quantitatively. Furthermore, the extracted species were estimated as neutral hydrated complexes M(tta)(2)(H(2)O)(n) (n= 1 or 2) for M = Ni, Cu and Pb and anionic complexes M(tta)(3)(-) for M = Mn, Co, Zn and Cd.

An imidazole-based P–N bridging ligand and its binuclear copper(I), silver(I) and palladium(I) complexes: synthesis, characterizations and X-ray structures

Abstract Reaction of 1-methylimidazole with n-BuLi in tetrahydrofuran at −78°C followed by addition of chlorodiphenylphosphine afforded a P–N bridging ligand, 2-(diphenylphosphino)-1-methylimidazole (dpim) in good yield. The structure of the ligand was determined by single crystal X-ray analysis. Reaction of a stoichiometric amount of the ligand with [Cu(MeCN)4]ClO4 in acetonitrile led to the binuclear complex [Cu2(μ-dpim)3(MeCN)](ClO4)2·2CH3CN (1·2CH3CN), whose structure was determined by single crystal X-ray analysis. The solid state structure shows that the two copper ions are held by three dpim ligands and the coordination geometry around each metal atom is different, one being three- and the other being four-coordinated. One of the copper ions forms a distorted tetrahedral array with two P and one N atoms from the dpim ligand and an additional N atom from an acetonitrile ligand, whereas the other copper ion is three coordinated with two N and one P atoms from the dpim ligand. The nitrate-bridged polymeric silver(I) complex, {[Ag2(μ-dpim)2(NO3)](NO3)}n (2) was prepared by the reaction of equimolar amounts of the ligand and silver nitrate in methanol and was characterized by IR, NMR and X-ray analysis. The dimeric unit, [Ag2(μ-dpim)2], possesses an eight-membered annular core structure with two ligands bridging the two metal ions in a head-to-tail configuration. Two types of nitrate ions are present in 2: one makes an infinite one-dimensional chain by joining the dimeric units through its two oxygen atoms in an anti–anti bridging mode whereas the other is disordered with a half occupancy and is located at the left and right sides of the chain. The dynamic behavior of 2 in acetone was also studied by variable temperature 31P NMR. The binuclear palladium(I) complex [Pd2Cl2(dpim)2] (4) was prepared by a conproportionation reaction between complex [PdCl2(dpim)2] (3) and [Pd(dba)2] (dba=dibenzylideneaceton). Only one geometric isomer, probably head-to-tail (HT), was formed in this reaction. Complex 3 was prepared by treating [PdCl2(PhCN)2] with two moles of ligand in dichloromethane solution. In this complex the ligand acts as a P-monodentate. In solution it exists as a mixture of cis and trans isomers.

Ion-pair extraction behavior of divalent transition metal cations as charged complexes with N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane and its analogues

The use of neutral di-Schiff base ligands, N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) and its analogues, N,N′-bis[1-(2-pyridyl)ethylidene]-1,2-diiminoethane (BPEE) and N,N′-bis(2-pyridylmethylidene)-trans-1,2-diiminocyclohexane (BPIC), as complexation reagents for ion-pair extraction of divalent transition metal cations into nitrobenzene with picrate anion was investigated. The results of numerical analysis concerning the extraction behavior indicated that they act as imine-N bidentate ligands in the extraction system. Furthermore, the introduction of the alkyl substituents onto imine-C on BPIE led to the change in the extraction selectivity by steric distortion of the cationic complexes, whereas that onto ethylene-C only caused the enhancement of the extractability.

Sulfonamide-type di-Schiff base ligands as chelate extraction reagents for divalent metal cations

Abstract The nature of sulfonamide-type di-Schiff base ligands, such as N,N′-bis[phenyl[o-(p-toluenesulfonamido)phenyl]methylidene]ethylenediamine (H2tsben-Ph2) and its analogs, as chelate extraction reagents for divalent metal cations such as Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ was investigated including comparison with that of respective phenol-type ones. These sulfonamide-type ligands acted as dianionic-quadridentate ones to form 1:1 complexes with the divalent cations in the system, which were confirmed from numerical analysis of relationship between distribution ratio of the metals and pH or ligand concentration. Furthermore, they showed unique extraction selectivity that extraction performance for Ni2+ was suppressed and that for Zn2+ was enhanced, which is originated mainly from the use of sulfonamide-donors on the complexation. This tendency was remarkable on H2tsben-Ph2 ( log K ex =−10.57±0.11 for Zn2+), and may be controlled by structural rigidity of the ligands including spread of π-conjugation system including the sulfonamide-donor.

Selective extraction of gallium from aluminum and indium using tripod phenolic ligands

Solvent extraction of trivalent group 13 metal cations such as aluminum, gallium and indium with tripod quadridentate phenolic ligand, tris(2-hydroxy-3,5-dimethylbenzyl)amine (H(3)tdmba), was investigated as fundamental study for their mutual separation. Gallium was extracted almost quantitatively as Ga(tdmba) (logK(ex)=-6.66+/-0.06 on using chloroform as extraction solvent), whereas aluminum and indium were hardly extracted due to steric hindrance on complexation of them with the ligand. The extracted Ga species was estimated as trigonal bipyramidal complex with one H(2)O molecule. Furthermore, extractability of Ga was increased by changing the ligand to more acidic tris(5-chloro-2-hydroxy-3-methylbenzyl)amine (H(3)tcmba) (logK(ex)=-6.18+/-0.18 on using dichloroethane as extraction solvent).

Ion-pair extraction behavior of transition metal(II) cations as charged complexes with ethylenediamine derivatives having heterocyclic pendant arms

Abstract The use of N , N , N ′, N ′-tetrakis(1′-pyrazolylmethyl)-1,2-diaminoethane (tpzen), N , N , N ′, N ′-tetrakis(3′,5′-dimethylpyrazol-1′-ylmethyl)-1, 2-diaminoethane (Me 8 tpzen) and N , N , N ′, N ′-tetrakis(2′-pyridylmethyl)-1,2-diaminoethane (tpen) as complexation reagents for ion-pair extraction of metal(II) cations into nitrobenzene was investigated. The order of extractability of the metals was tpen > Me 8 tpzen > tpen. Although these molecules have four nitrogen-containing heterocyclic pendant arms and act as sexadentate ligands normally in aqueous solution, the result of numerical analysis concerning the extraction behavior indicated that they act as bidentate ligands in the extraction system. The pendant arms were not concerned in chelate formation and the arms acted to raise the hydrophobicity and the extractability of the complexes.

Separation and determination of trace amounts of barium as its thenoyltrifluoroacetone complex with dibenzo-18-crown-6 by means of synergistic extraction and flame photometry

SummaryA new method for the separation and determination of trace amounts of barium at the ppb-ppm level in water as its thenoyltrifluoroacetone (TTA) complex with dibenzo-18-crown-6 (DB18C6) comprises synergistic extraction and back extraction combined with flame photometry. The effect of various factors (solvent, size of crown ether, reagent concentration, shaking time, preconcentration factor, foreign ions etc.) on the extraction and back extraction of barium has been investigated. The barium TTA chelate in o-dichlorobenzene forms stable adducts with DB18C6 [Ba(TTA)2 · nDB18C6, n=1∼2]; the stability constants (βn) of the adducts determined by means of the curve fitting method are log β1=3.77 and log β2=7.91. The content of barium in sodium chloride and sodium nitrate of guaranteed reagent grade was found to be 9.67±0.08 μg/g and 7.86±0.09 μg/g, respectively.

A new tripod PPN bridging ligand and its copper, silver and palladium complexes: syntheses, characterizations and X-ray structures

Abstract A new tripod bridging ligand 2-{bis(diisopropylphosphino)methyl}-1-methylimidazole, MeImCH(Pi-Pr2)2 (PPN) was synthesized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-1-methylimidazole and chlorodiisopropylphosphine. The dicationic dinuclear complex [Cu2(PPN)2][ClO4]2 (1) was prepared by the reaction of the ligand with [Cu(MeCN)4]ClO4 in acetonitrile. The reaction of the ligand with AgNO3 in propane-2-ol followed by addition of NH4PF6 led to the formation of a similar type complex [Ag2(PPN)2][PF6]2 (2). The X-ray diffraction studies of 1 and 2 revealed a μ2-η1:η2 tripod-like bonding of the PPN ligand, with one P and one N atom chelating to one metal ion and the remaining one P atom binds to another metal ion, affording a face-to-face type molecule. An eight-membered M2P4C2 and a 10-membered M2P2N2C4 ring are thus formed with this new functional diphosphine ligand. In both complexes the two metal ions are held in very close proximity [2.6707 A for 1 and 2.859(3) A for 2]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinuclear complexes the ligand also afforded a mononuclear palladium complex, [PdCl2(PPN)] (3), when it was treated with an equimolar amount of [PdCl2(PhCN)2] in benzene. In 3 the ligand acts as a bidentate chelate through its two phosphorus atoms, leaving the imidazole donor dangling. On the other hand, a P,P-bridged dinuclear Pd(I) complex [Pd2Cl2(PPN)2] (4) was achieved by reacting two moles of the ligand with one mole of [PdCl2(PhCN)2], followed by the addition of one mole of Pd(dba)2 [dba=dibenzylideneacetone].

Ion chromatography using a charged complex anion-exchange group

Abstract Novel ion chromatography using a cationic coordination–unsaturated (hydrated) complex immobilized on a packing material as an anion-exchange group was investigated. This group, named as ‘charged complex anion-exchange group (CCAG)’, has not only normal anion-exchange ability, but also ligand-exchange ability because of its Lewis-acidic nature, and this novel chromatographic system can have specific anion-exchange selectivity different from normal anion chromatography. Several CCAGs, such as copper(II) and cadmium(II) complexes with bis(2-pyridylmethyl)amino group bonded on a hydrophilic vinyl polymer, showed unique anti-Hofmeister-type selectivity patterns for monovalent inorganic cations. During chromatographic comparison between many CCAGs formed from various divalent metal cations and several immobilized ligands having 2-pyridylmethyl and/or 2-quinolylmethyl pendant arm(s), it was found that the anion-exchange selectivity of CCAGs is controlled mainly by the hardness/softness of their central metal cations as Lewis acids, and their steric nature such as extent of shielding on their ligand-exchange cite and their steric bulkiness. Furthermore, the use of CCAGs formed from these metals and N,N-bis(2-pyridylmethyl)octadecylamine pre-coated on a reversed-phase HPLC column was discussed.

Highly sensitive spectrofluorometry of europium(III) as its benzoyltrifluoroacetone complex with trioctylphosphine oxide by means of solvent extraction and vacuum sublimation

SummaryA new method for the highly sensitive fluorometric determination of europium(III) as its benzoyltrifluoroacetone (BFA) complex with trioctylphosphine oxide (TOPO) without uncombined BFA in n-hexane has been established by means of solvent extraction and vacuum sublimation. The effect of various factors on the fluorescence intensity of europium(III) was investigated. The fluorescence intensity was measured at 620 nm against rhodamine B as an internal standard under the excitation at 335 nm. It was found that a heating treatment gave rise to the enhancement of the fluorescence intensity for about twice times compared with that without heating treatment. Excellent linearity of the calibration curve of europium(III) was obtained in the range of 0–100 ppb. A few ppb of europium(III) can still be detected with this method. All 13 rare earth metals and cobalt(II) tested gave a somewhat positive error. Aluminium(III), iron(III), and copper(II) caused a negative error. The interference of aluminium(III) and iron(III) was removed by extraction with 0.1 mol/l 8-quinolinol in chloroform at pH 4.0, while the problem of cobalt(II) and copper(II) was solved by masking with 0.1 mol/l Na2S2O3 in aqueous solution.