Terdentate Ligand Research Articles

Easy synthesis of ‘half-units’: their use as ligands or as precursors of non-symmetrical Schiff base complexes

This paper is devoted to a particular reaction able to give singly condesed Schiff base derivatives of ß-diketones (called ‘half-units’) in an easy way. Indeed, 1,2-diamino-2-methylpropane, which possesses an amine function sterically hindered by two methyl groups, reacts with a diketone such as 2,4-pentanedione or 2-hydroxyacetophenone only by its non-hindered amine function, yielding a ‘half-unit’. In a following step, this terdentate ligand can react with an aldehyde function to give a non-symmetrical tetradentate Schiff base. Such a reaction can be performed on the free ‘half-unit’ or on its ‘complexed form’. Some examples of nickel and copper complexes are given. A particular interest has been given to the use of imidazole-2-carboxaldehyde which yields non-symmetrical Schiff base complexes with a free nitrogen atom not included in the N 3O coordination site. According to the procedure of ‘complexes as ligands’, it is possible to isolate bimetallic complexes with imidazole bridges. Their genuine identity has been confirmed by NMR (nickel) and also by thermal variation of the magnetic susceptibility (copper).

Thermodynamic stability and formation mechanism of iron(III) complex with N-pyridoxyl- o-hydroxyaniline: role of phenolate oxygen on the enhancement of the stability

A new terdentate ligand, N-pyridoxyl- o-hydroxyaniline ( 1, H 2pha), was synthesized and the formation of its iron(III) complex was thermodynamically and kinetically investigated (0.10 mol dm −3 NaClO 4; 25°C). The ligand forms a very stable bis(ligand)iron(III) complex (log β 12 = 45.8±0.2; β 12 (mol −2 dm 6) = [Fe(Hpha) 2 +]/[Fe 3+][Hpha −] 2) in comparison with other N α -pyridoxyl-L-amino acid-type terdentate ligands with benzyl ( 2), methyl ( 3), and indolylmethyl ( 4) groups, indicating that an intramolecular interaction as well as a high affinity of phenolato oxygen to the central metal atom greatly contributes to the stability of the bis(ligand)iron(III) complex of 1. The rate constants for the iron(III) complex of 1 are (1.40±0.20) × 10 2 mol −1 dm 3 s −1 for the two parallel pathways of Fe 3+ + H 3pha + ( k 33) and FeOH 2+ + H 4pha 2+ ( k 24) ( k 33 + k 24 K OH 11 Ka (amNH), where K OH 11 and Ka (amNH) are the hydrolysis constant of iron(III) and protonation constant of 1 at the amino nitrogen) and (2.44±0.30) × 10 2mol −1 dm 3 s −1 for the pathway of FeOH 2+ + H 3pha + ( k 23). The comparison of these rate constants with those of the iron(III) complexes of 2, 3, and 4 suggest that the complex formation mechanism is given by the rate-determining coordination of the phenolato oxygen of pyridoxyl moiety to iron(III), followed by the rapid donations of other ligating groups.

Synergistic Extraction of Rare Earths(III) with β-Diketone and Nitrogen-Containing Terdentate Ligand, 2,2′:6′,2″-Terpyridine

Abstract The synergistic extraction of rare earth(III) ions (RE: La, Sm, Tb, and Lu) was investigated using a β-diketone (HA), i.e., trifluoroacetylacetone (Htfa) or hexafluoroacetylacetone (Hhfa), in the presence of a terdentate ligand, 2,2′:6′,2″-terpyridine (terpy) into benzene. The formation of complexes such as RE(A)2+ or RE(A)2+ in the aqueous phase was observed. The synergistic enhancement is attributed to the formation of an adduct RE(A)3terpy in the benzene phase. The adduct formation constants (βS,1) and the synergistic extraction constants were determined. For each RE(III), the βS,1 value in the Htfa–terpy system is smaller than that in the Hhfa–terpy system. The βS,1 values decrease with increasing atomic number of RE(III) in the Htfa–terpy system, but the βS,1 value for La(III) is smaller than that for the other RE(III) in the Hhfa–terpy system.

STRUCTURES AND PROPERTIES OF COPPER(II) COMPLEXES WITH IMINODIACETATO AND IMIDAZOLE OR RELATED LIGANDS. I. CRYSTAL STRUCTURE OF AQUA(IMIDAZOLE) (IMINODIACETATO)COPPER(II) MONOHYDRATE AND (IMIDAZOLE)(N-CARBOXYMETHYL-D,L-THREONINATO)COPPER(II)

Abstract The crystal structures of two mixed-ligand copper(II) complexes having iminodiacetate(2-) (IDA) or N-carboxymethyl-D,L-threoninato(2-) ion (CMT) as terdentate ligands and imidazole (ImH) as an N-heterocyclic ligand are reported. Both compounds crystallize in the orthorhombic system, space group Pbca with Z = 8. Aqua(imidazole)(iminodiacetato)copper(II) monohydrate (I,R = 0.065, R w = 0.075) consists of H2O molecules and [Cu(IDA)(ImH)(H2O)] complex units in a hydrogen bonding network. The structure of imidazole(N-carboxymethyl)-D,L-threoninatocopper(II) (IV, R = 0.066, Rω 0.078) is built up of hydrogen bonded polynuclear chains. In both compounds the Cu(II) ion exhibits a flattened and distorted square-based pyramidal coordination, with a terdentate aminoacidate ion, IDA or CMT, and one ImH ligand at the base and H2O (in I) or the oxygen atom of the OH side chain from one adjacent CMT ion (in IV) as the fifth apical ligand. The nearly coplanar conformation of the two five-membered chelate rings in I and IV is discussed in connection with the known structure of corresponding aquacomplexes (with H2O instead of ImH) and the ability of terdentate aminoacids to give ternary Cu(II) complexes having two N-heterocyclic donors (2 ImH or one 2,2′-bipy) per Cu(II) atom.

Crystal structures of the solvates trans-[RhCl 2(MeOH){C 6H 3-2,6-(CH 2PCy 2) 2}]. 0.41CH 2Cl 2 and trans-[RhCl 2(EtOH){C 6H 3-2,6-(CH 2PCy 2) 2}]. H 2O. Factors influencing the reactions of C 6H 4-1,3-(CH 2PR 2) 2 with RhCl 3

The terdentate ligands C 6H 3-2,6-(CH 2PCy 2) 2 (PCP: Cy = cyclohexyl) in the octahedral solvento complexes trans-[RhCl 2(MeOH)(PCP)] and trans-[RhCl 2(EtOH)(PCP)] adopt conformations which minimise the interactions between the sterically demanding Cy groups and the trans chlorides. Comparison of these structures with those of related molecules, including square-pyramidal and square-planar species, suggests an explanation for the different structural types obtained as products from reactions of RhCl 3.3H 2O and various ligands C 6H 4-1,3-(CH 2ER 2) 2 with E = N or P.

Kinetics and mechanism of complex formation reaction of iron(II) with 4-methyl-8-DI(Carboxymethyl)aminomethyl umbelliferrone: Role of the fourth chelating group in tripodal (NO 3)-type tetradentate ligand structure on the stabilization of the iron(II) complex

Thermodynamic stability and kinetics and mechanism of the formation of the iron(II) complex of 4-methyl-8-di(carboxymethyl)aminomethyl umbelliferrone ( 1, H 3muia) have been studied spectrophotometrically in an aqueous sodium perchlorate solution (0.10 mol dm −3) at 25°C. A 1:1 (metal:ligand) complex of iron(II) with 1 forms in an acidic medium with a stability constant, log β 11 (mol dm −3), of 14.42±0.20, in contrast to no formation of the iron(II) complex with related terdentate ligands having a mono(carboxymethyl) ligating group. This complex formation reaction proceeds through a single pathway of Fe 2+ with Hmuia 2− ligand species with a rate constant, k 2 (mol −1 dm 3 s −1), of (7.04±0.20) × 10 4. The coordination reaction mechanism is discussed in detail.

The Benzodiphosphaalkene Ligand and Its PdII and PtII Complexes: Their Synthesis, Structure, and an ESR Study of Their Reduction Products

The new diphosphaalkene 1,3-bis[2-(2,4,6-tri-tert-butylphenyl)phosphanediylmethyl]benzenLe,, h as been synthesized. Due to the presence of two P=C bonds three isomers (EE, EZ, ZZ) were observed by 31P NMR, and the crystal structures of two of them could be determined (EE, ZZ). The electrochemical behavior of L has been studied by cyclic voltametry: a quasi-reversible reduction occurs at -1.89 V/SCE and corresponds to the formation of a radical anion which has been studied by ESR at variable temperature. The experimental 31P and 'H hyperfine constants are consistent with free rotation about the P=C and Cphosphaalkene-Cbenzene bonds at room temperature and agree with ab initio predictions. One of the isomers of L forms complexes with palladium(I1) and platinum(I1) ions. The crystal structures show that L is orthometalated and acts as a terdentate ligand by coordinating the metal with each phosphorus atom. These complexes are electrochemically reduced between -0.92 and - 1.29 V, and the resulting paramagnetic species are studied by ESR in liquid and frozen solutions. This reduction process was shown to be a ligand-centered process, an appreciable part of the unpaired electron is localized on each of the phosphaalkene carbons (20%) and phosphorus atoms (5%).

Preparation and crystal structure of trans-[NiBr{C 6H 3-2,6-(CH 2PCy 2) 2}

The synthesis of trans-[NiBr{C 6H 3-2,6-(CH 2PCy 2) 2}], Cy = cyclohexyl, and its characterisation by spectroscopy and single crystal X-ray analysis are described. The constraints imposed by the bulky terdentate ligand lead only to minor distortions of the square planar nickel(II) coordination (PNiP = 161.6(1)°). The nickel coordination is compared with those found in related complexes with terdentate N- and P-donor ligands.

Synthesis and physicochemical studies of the chloride and bromide complexes of yttrium and lanthanides with 4-N-(4′-antipyryl-methylidene)aminoantipyrine

Twenty new complexes of chlorides and bromides of yttrium and lanthanides with the Schiff base 4-N-(4′-antipyrylmethylidene)aminoantipyrine (AA) have been prepared and characterised. They have the general formula, [Ln(AA)2Cl3] and [Ln(AA)2Br2]Br where Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho and Er. Molar conductance studies indicate slight dissociation for the chloride complexes and 1:1 electrolytic behaviour for the bromide complexes. The magnetic moments of all the complexes agree well with Van Vleck values. The infrared spectra reveal that AA functions as a terdentate ligand in all these complexes coordinating through the oxygens of both the carbonyl groups and the azomethine nitrogen. Electronic spectra of Nd, Ho and Er for the chloride complexes and that of Pr, Nd, Ho and Er for the bromide complexes show weak covalency in the metal-ligand bond.

Substitution of nitrido by the oxo group in reactions of [ReNCl2(PPh3)2] with multidentate N,O–-donor chelates. Crystal structure of [ReOCl2(PPh3)(HL)][H2L = 2,6-bis(hydroxymethyl)pyridine

The complex [ReNCl2(PPh3)2] reacts with the potentially bidentate 8-hydroxyquinoline (Hquin) and N-phenylsalicylideneimine (Hpsal), and potentially terdentate ligands di-2-pyridyl ketone and 2,6-bis(hydroxymethyl)pyridine (H2L) to form the products [ReOCl(quin)2], [ReOCl2(PPh3)(psal)], [ReOCl2{(C5H4N)2C(O)(OH)}] and cis-[ReOCl2(PPh3)(HL)], respectively. The first three products are identical to those isolated earlier by the reactions of trans-[ReOCl3(PPh3)2] with these ligands, while in the latter product the HL– ligand acts as a bidentate N,O–-donor, spanning one axial (O–trans to ReO) and one equatorial co-ordination site. These reactions present an alternative synthetic route to monooxorhenium(V) complexes. The complexes cis-[ReOCl2(PPh3)(HL)] crystallizes in the orthorhombic space group P212121 with cell parameters a= 10.019(3), b= 12.457(6), c= 19.53(1)A, U= 2436.5 A3, Z= 4, R= 0.059 and R′= 0.074 for 1330 reflections with Fo > 4σ(Fo).

Conventional and cyclometallated complexes of ruthenium(II) with ambidentate terdentate ligands displaying N3 or N2C binding modes

The potentially terdentate N-donor ligands 6-(2-dimethylaminophenyl)-2,2′-bipyridine (L1) and 2-(2-dimethylaminophenyl)-1,10-phenanthroline (L2), which comprise a dimethylaminophenyl group attached to 2,2′-bipyridine or 1,10-phenanthroline fragments respectively, have been prepared. The ruthenium(II) complexes [RuL2][PF6]2(L = L11 or L22) and [RuL(L - H)][PF6](L = L13 or L24) have been prepared and characterised by conventional spectroscopic, electrochemical and X-ray diffraction methods. In complexes 1 and 2 the ligands both co-ordinate in the expected N3-donor mode to give RuN6 centres. The Ru–N(amine) bonds (2.22 and 2.24 A respectively) are considerably longer than the Ru–N(pyridine) bonds (2.0–2.1 A). In complexes 3 and 4 one ligand is bound as a conventional N3 donor, but in the second the phenyl ring is turned around such that it co-ordinates in a cyclometallated fashion via C6 with the NMe2 substitutent directed outwards. The Ru–C bonds (ca. 2.03 A) are similar in length to typical Ru–N(pyridine) bonds, and their strongly electron-donating capability results in a lengthening of the trans Ru–N bonds. Detailed comparison of the structures of 1 with 3, and 2 with 4, allows the structural effects of cyclometallation to be clarified. The RuII–RuIII couples for 1 and 2 are cathodically shifted by ca. 0.1 V with respect to the RuN6 centre of [Ru(terpy)2]2+(terpy = 2,2′ :6′,2″-terpyridine) which is consistent with the greater σ-donating and poorer π-accepting characteristics of tertiary amine ligands compared to pyridines; for 3 and 4, where the formally anionic carbon donor is a much stronger σ donor, the RuII–RuIII couple is shifted cathodically by a further 0.84 V in each case. The electronic spectra of 1–4 are also discussed.

Partially encapsulated copper(I) complexes of mono(o-aryl)-substituted derivatives of 2,2′-bipyridine and 1,10-phenanthroline

Copper(I) complexes of the potentially terdentate ligands 6-(2-dimethylaminophenyl)-2,2′-bipyridine (L1) and 2-(2-dimethylaminophenyl)-1,10-phenanthroline (L2), [CuL2][PF6](L = L11 or L22) have been prepared. Both complexes have highly distorted tetrahedral structures in which only the α,α′-diimine fragments are co-ordinated; the C6H4NMe2 fragments are pendant, and are twisted with respect to the co-ordinated bipyridine and phenanthroline fragments such that the pendant aromatic ring of one ligand lies stacked with the co-ordinated fragment of the other ligand. This results in ‘partial encapsulation’ of the copper(I) centres which confers chemical stability (no autoxidation in the presence of O2) and electrochemical stability (wide ‘redox-existence ranges’ for the CuI oxidation states) on the complexes. The inter-ligand stacking also results in distortion away from pseudotetrahedral geometry at the metal centres towards square planar (θ, the angle of intersection of the two CuN2 planes, is 75° for 1 and 76° for 2); 1H NMR and electronic spectra show that this is maintained in solution. Neither complex is luminescent at room temperature, possibly due to intramolecular quenching via transient co-ordination of the pendant amine groups. Oxidation of 1 and 2 to the copper(II) complexes 1+ and 2+ with ferrocenium affords stable solutions whose EPR spectra indicate that the metals now have geometries that are much more flattened towards square-planar geometry; this would not be possible with more highly encapsulated complexes of bipyridines or phenanthrolines with two pendant aryl substituents in the ortho positions.

New Soluble Polysiloxane Polymers Containing a Pendant Terdentate Aryldiamine Ligand Substituent Holding a Highly Catalytically Active Organometallic Nickel(II) Center

A new type of grafted polysiloxane polymer is described in which an aryldiamine substituent, [CsH3(CHzNMe2)2-2,61-, provides a pendant terdentate ligand environment for a catalytically active (0rgano)nickel center. The novel strategy employed involves initial grafting of the aryl bromide 5-amino-2-bromo-1,3-bis[(dimethylamino)methyllbenzeinnet o the side chain of poly((2-(chlorocarbonyl)ethyl)methylsiloxane~f ollowed by nickel incorporation through an oxidative addition reaction with [Nio(COD)21 (COD = cycloocta-1,5-diene). Soluble polymers with different amounts of nickel incorporation have been prepared and characterized by NMR, FT-IR, and W/vis spectroscopy as well as by differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). These polymeric materials having an immobilized organonickel(I1) center show good catalytic activity in the Kharasch addition reaction of polyhalogenated alkanes to alkenes that is of the same order of magnitude as for the comparable model organonickel(I1) complex [Ni{ CsH2(CH2NMe2)2-2,6-N(H)C(O)- Me-4)BrI.

CRYSTAL STRUCTURE AND INFRARED SPECTRA OF A LANTHANUM COORDINATION COMPOUND WITH GLYCINE, {[La(Gly)s·2H2O]·(ClO4)3}n

Abstract A lanthanum coordination compound with glycine {[La(Gly)3·2H2O]·(ClO4)3}n (Gly = NH+ 3-CH2-COO−) was synthesized and obtained in the form of single crystals. Its X-ray crystal structure has been determined and the IR spectrum has been studied. Crystallographic data for the compound are Mr = 698.6, triclinic, space group Pi, with a = 10.730(4), b = 12.958(4), c = 8.806(3) A, a = 97. 10(2), β = 113.05(3), γ = 71.52(3)°, V = 1068.55 (0.67) As, Z = 2; D calc = 2.17 cm−3, μ = 25.1 cm−1; T = 298K; λ(MoKα). = 0.71069 A, 2 θmax = 60.0°. Final R = 0.044 for 5554 observed reflect with I > 3σ (I). Glycine molecules coordinate with lanthanum atoms through alternate “two-four carboxylate bridges” to form a one-dimensional chain compound of infinite length. Some of the glycine molecules coordinate to lanthanum atoms as bridging bidentates ligands and the others as bridging-chelating terdentate ligands. The IR spectrum of the compound is compared with that of {[Sm2(Gly)6·4H2O]·(ClO4)6·5H2O}n. Differences in the...

O-hydroxyaroyl-isonicotinoyl hydrazones as chelating agents with divalent transition metal ions

Two series of bivalent metal complexes of the type M(Sal)· xH2O and M(Naph) have been synthesized; where M = Co, Ni, Cu, Zn, Pd and Cd, and H2-Sal and H2-Naph are salicylaldehyde and o-hydroxynaphthaldehyde isonicotinoyl hydrazones which acted as dibasic terdentate ligands. The polymeric nature and coordination sites of the complexes have been characterized by elemental, d.t.a. and t.g.a analyses, molar conductance, pH, room temperature magnetic susceptibility and spectral (i.r., 1H n.m.r, u.v.) measurements. The protonation constants of the ligands have been determined potentiometrically at different temperatures, ionic strengths and at different EtOH-H2O compositions.

Organonickel(II) complexes containing aryl ligands with chiral pyrrolidinyl ring systems; syntheses and use as homogeneous catalysts for the Kharasch addition reaction

AbstractNew chiral organonickel(II) complexes 3a‐d have been synthesized containing monoanionic terdentate ligands of the type 2,6‐bis[(1‐pyrrolidinyl)methyl]phenyl. Chirality is introducedmagnified imageat the nitrogen donor atoms, which are part of the pyrrolidinyl ring systems, by placing substituents on the 2 or 5 positions of the rings. The complexes have been characterized variously by 1H‐ and 13C‐NMR spectroscopy, UV/Vis spectroscopy and X‐ray crystallography.Crystals of 3b are monoclinic, space group P21, with a = 11.572(2), b = 11.804(2), c = 13.249(3) Å, β = 107.00(2)°, Z = 4, final R = 0.043 for 3043 observed reflections. Crystals of 3c are tetragonal, space group P412121, with a = b = 12.2957(14) Å, c = 26.418(3) Å, Z = 8, final R = 0.052 for 1479 observed reflections. Crystals of 3d are tetragonal, space group P412121, with a = b = 11.0869(5), c = 21.718(2) Å, Z = 4, final R = 0.046 for 1469 observed reflections.The catalytic ability of the nickel complexes in the addition reaction of polyhalogenated compounds with alkenes (Kharasch addition) is markedly influenced by the geometry around the nickel atom and only 3a and 3b prove to be effective catalysts. The highest enantiomeric excesses of 16‐17% obtained with 3b and L‐menthyl methacrylate in this catalytic reaction indicate that the C2 chiral fence produced by the Me‐substituted pyrrolidinyl rings is not very effective for the transfer of chiral information.

Solvation and reactivity of iron(II)–diimine complexes in dimethyl sulfoxide–water mixtures

Kinetics of the base hydrolysis of several iron(II)–diimine complexes, including two with terdentate ligands and one with an encapsulating ligand, and of the peroxodisulfate oxidation of three ternary iron(II)–diimine–cyanide complexes, are reported for reaction in dimethyl sulfoxide (DMSO)–water mixtures at 298.15 K. Solubilities of simple and complex salts have been determined in these mixtures, both to extend the range of simple and complex ion-transfer chemical potentials and to provide the basis for initial-state/transition-state analyses of reactivity trends for several of the base hydrolysis and peroxodisulfate oxidations. Cases are identified where the destabilisation of hydroxide ions, OH–(aq), by added DMSO increases the rate of base hydrolysis. We also identify cases where compensation effects result in only a small change in rate constant for oxidation by peroxodisulfate where DMSO is added.

Synthesis and characterization of ruthenium complexes which utilize a new family of terdentate ligands based upon 2,6-bis(pyrazol-1-yl)pyridine

To demonstrate the synthetic utility of a new family of terdentate ligands based on 2,6-bis(pyrazol-1-yl)pyridine (bpp), reaction conditions were developed to generate a variety of [RuL(NO2)(PMe3)2]+ complexes [L = bpp, 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine(bdmpp), 2,6-bis(3-phenylpyrazol-1-yl)pyridine (bppp) or 2,6-bis(3-p-chlorophenylpyrazol-1-yl)pyridine (bcppp)]. These complexes were characterized by elemental analysis, 1H and 13C NMR, infrared and UV/VIS spectroscopies, cyclic voltammetry, and single-crystal X-ray diffraction studies. The substituents of the terdentate bpp ligands sterically affected the Ru–N(pyrazole) bond lengths, the displacement of the nitrogen atoms of the nitro ligands from the RuL plane, and the twisting of the N–O vectors of the nitro ligand from that plane. Also the substituents affected the potentials and peak-current ratios of the RuIII–RuII couples. The log (ipc/ipa) values (ipc= cathodic peak current, ipa= anodic peak current) are linearly correlated with the steric size of the substituents as estimated by Tolman's cone angles and with the distance of the nitro ligand out of the RuL plane. A linear correlation was also found between the differences in infrared absorbances due to the N–O symmetric and asymmetric stretches and the ratio of the N–O bond distances observed from the four crystal structures.

Halogenotrimethylplatinum(IV) complexes of 2,6-bis(p-tolylthiomethyl)pyridine (L1): nuclear magnetic resonance studies of their solution state stereodynamics and the crystal structure of fac-[PtBrMe3L1

Under mild conditions 2,6-bis(p-tolylthiomethyl) pyridine (L1) reacted with halogenotrimethylplatinum(IV) to afford complexes of the type fac-[PtXMe3L1](X = Cl or Br). This potentially terdentate ligand acts here in a five-membered S/N chelate bidentate fashion. Solution dynamic NMR studies revealed the presence of three fluxional processes: pyramidal inversion of the co-ordinated sulfur atom, S-S switching with correlated pyramidal inversion, and S-S switching. The mechanism for the S-S exchange process was elucidated by two-dimensional NMR exchange spectroscopy. The crystal structure of fac-[PtBrMe3L1] confirms the bidentate chelate nature of the ligand in the solid state, with a N-Pt-S(1) angle of 81.5°. IR data for the Pt-C, Pt-N and Pt-X stretching modes in these complexes are also presented.

Matrix effects on palladium(II) chelation by two macroporous polystyrene resins with 2,6-bis(methylthiomethyl) pyridine groups

Two commercially available macroporous polystyrenes (3% DVB) with different physical characteristics, Janssen-MPs and XAD-2, have been chloromethylated and subsequently reacted with the terdentate ligand 2,6-bis(methylthiomethyl)-3-hydroxypyridine. The level of functionalization as well as the sorption ability of the resulting chelating resins (MPs-SNS and XAD-2-SNS) towards Pd(II) from acidic chloride aqueous solutions strongly depend on the morphology of the polymeric matrices. Despite a lower functionalization degree, the XAD-2 based chelating resin, derived from a polymeric support with higher surface area and lower pore average diameter, showed higher performances. Both uptake of Pd(II) and stripping of the sorbed Pd(II) were fairly rapid, indicating a better accessibility to the chelating sites. The saturation capacity suggests the formation of a 1:1 complex. In addition, the XAD-2 based resin displays superior selectivity in the extraction of Pd(II) from mixtures of Pd(II)-Cu(II) at pH 1, essentially quantitative separation of Pd(II) being achieved even with Cu(II) present in 150-fold excess. The sorption levels of Fe(III), Co(II), Ni(II) and Zn(II) at pH 1 were not detectable.