From Gas Phase Observations to Solid State Reality: The Identification and Isolation of Trinuclear Salicylaldoximato Copper Complexes.

Conditions have been identified in which phenolic aldoximes and ketoximes of the types used in commercial solvent extraction processes can be doubly deprotonated and generate polynuclear Cu complexes with lower extractant:Cu molar ratios than those found in commercial operations. Electrospray mass spectrometry has provided an insight into the solution speciation in extraction experiments and has identified conditions to allow isolation and characterization of polynuclear Cu-complexes. Elevation of pH is effective in enhancing the formation of trinuclear complexes containing planar {Cu-μ-O} or {Cu-μ-OH} units.

Proton Chelating Ligands Drive Improved Chemical Separations for Rhodium.

Current methods for the extraction of rhodium carry the highest carbon footprint and worst pollution metrics of all of the elements used in modern technological applications. Improving upon existing methods is made difficult by the limited understanding of the molecular-level chemistry occurring in extraction processes, particularly in the hydrometallurgical separation step. While many of the precious metals can be separated by solvent extraction, there currently exist no commercial extractants for Rh.

Reversible Pressure-Controlled Depolymerization of a Copper(II)-Containing Coordination Polymer.

A unique pressure-induced Cu-N bond breaking/bond forming reaction is reported. The variation of pressure on a single crystal of a one-dimensional copper- (II)-containing coordination polymer (Cu L (1-methylpiperazine) ] , where H L is 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione)), was monitored using single crystal X-ray diffraction with the aid of a diamond anvil cell. At a very low elevated pressure (≈0.

Ditopic receptors containing urea groups for solvent extraction of Cu(ii) salts.

The ditopic receptor L3 [1-(2-((7-(4-(tert-butyl)benzyl)-1,4,7,10-tetraazacyclododecan-1-yl)methyl)phenyl)-3-(3-nitrophenyl)urea] containing a macrocyclic cyclen unit for Cu(ii)-coordination and a urea moiety for anion binding was designed for recognition of metal salts. The X-ray structure of [CuL3(SO)] shows that the sulfate anion is involved in cooperative binding via coordination to the metal ion and hydrogen-bonding to the urea unit. This behaviour is similar to that observed for the related receptor L1 [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea], which forms a dimeric [CuL1(μ-SO)] structure in the solid state.

A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources.

Waste electrical and electronic equipment (WEEE) such as mobile phones contains a plethora of metals of which gold is by far the most valuable. Herein a simple primary amide is described that achieves the selective separation of gold from a mixture of metals typically found in mobile phones by extraction into toluene from an aqueous HCl solution; unlike current processes, reverse phase transfer is achieved simply using water. Phase transfer occurs by dynamic assembly of protonated and neutral amides with [AuCl4 ](-) ions through hydrogen bonding in the organic phase, as shown by EXAFS, mass spectrometry measurements, and computational calculations, and supported by distribution coefficient analysis.

A Comparison of the Selectivity of Extraction of [PtCl6](2-) by Mono-, Bi-, and Tripodal Receptors That Address Its Outer Coordination Sphere.

Extraction and binding studies of [PtCl6](2-) are reported for 24 mono-, bi-, and tripodal extractants containing tris(2-aminoethyl)amine (TREN) or tris(3-aminopropyl)amine (TRPN) scaffolds. These reagents are designed to recognize the outer coordination sphere of [PtCl6](2-) and to show selectivity over chloride anion under acidic conditions. Extraction from 0.

Preorganized tridentate analogues of mixed hydroxyoxime/carboxylate nickel extractants.

A series of 22 tridentate unsaturated mono-anionic ligands having the atom-sequence Y-C[double bond, length as m-dash]C-N=CH-C=C-Z(-1), with Y = N, O, or S and Z = O or S, has been studied to establish whether this backbone could be used to develop strong solvent extractants for nickel(II) which will preferably also show a high selectivity over iron(III) in the pH-dependent process: 2LH(org) + NiSO4 ⇌ [(L)2Ni]org + H2SO4. All are capable of forming octahedral [(L)2Ni] complexes with a mer-arrangement of the YNZ(-1) donor set. X-ray crystal structures of three salicylaldimine proligands derived from 3-bromo-5-t-butyl-2-hydroxybenzaldehyde show these to have pre-organised donor sets in which the three donors are held in an approximately orthogonal arrangement by intramolecular hydrogen bonds.

Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants.

Alkyl-substituted phenolic pyrazoles such as 4-methyl-2-[5-(n-octyl)-1H-pyrazol-3-yl]phenol (L2H) are shown to function as Cu-extractants, having similar strength and selectivity over Fe(iii) to 5-nonylsalicylaldoxime which is a component of the commercially used ACORGA® solvent extraction reagents. Substitution in the phenol ring of the new extractants has a major effect on their strength, e.g.

Anion Receptor Design: Exploiting Outer-Sphere Coordination Chemistry To Obtain High Selectivity for Chloridometalates over Chloride.

High anion selectivity for PtCl6(2-) over Cl(-) is shown by a series of amidoamines, R(1)R(2)NCOCH2CH2NR(3)R(4) (L1 with R(1) = R(4) = benzyl and R(2) = R(3) = phenyl and L3 with R(1) = H, R(2) = 2-ethylhexyl, R(3) = phenyl and R(4) = methyl), and amidoethers, R(1)R(2)NCOCH2CH2OR(3) (L5 with R(1) = H, R(2) = 2-ethylhexyl and R(3) = phenyl), which provide receptor sites which extract PtCl6(2-) preferentially over Cl(-) in extractions from 6 M HCl solutions. The amidoether receptor L5 was found to be a much weaker extractant for PtCl6(2-) than its amidoamine analogues. Density functional theory calculations indicate that this is due to the difficulty in protonating the amidoether to generate a cationic receptor, LH(+), rather than the latter showing weaker binding to PtCl6(2-).

EPR/ENDOR and Computational Study of Outer Sphere Interactions in Copper Complexes of Phenolic Oximes.

Copper complexes of the phenolic oxime family of ligands (3-X-salicylaldoximes) are used extensively as metal solvent extractants. Incorporation of electronegative substituents in the 3-position, ortho to the phenol group, can be used to buttress the interligand H-bonding, leading to an enhancement in extractant strength. However, investigation of the relevant H-bonding in these complexes can be exceedingly difficult.

Catalytic epoxidation by perrhenate through the formation of organic-phase supramolecular ion pairs.

Organic-phase supramolecular ion pair (SIP) host-guest assemblies of perrhenate anions (ReO4(-)) with ammonium amide receptor cations are reported. These compounds act as catalysts for the epoxidation of alkenes by aqueous hydrogen peroxide under biphasic conditions and can be recycled several times with no loss in activity.

Solvent extraction: the coordination chemistry behind extractive metallurgy.

The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, M(n+), metalate anions, MXx(n-), or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes.

Exploiting outer-sphere interactions to enhance metal recovery by solvent extraction.

Interactions, particularly hydrogen bonds, between ligands in the outer coordination spheres of metal complexes have a major effect on their stabilities in the hydrocarbon solvents used in commercial solvent extraction and it is now possible to use these interactions to tune the strength and selectivity of extractants.

Outer-sphere coordination chemistry: amido-ammonium ligands as highly selective tetrachloridozinc(II)ate extractants.

Eight new amido functionalized reagents, L(1)-L(8), have been synthesized containing the sequence of atoms R(2)N-CH(2)-NR'-CO-R″, which upon protonation forms a six-membered chelate with a hydrogen bond between the tertiary ammonium N-H(+) group and the amido oxygen atom. The monocationic ligands, LH(+), extract tetrachloridometal(II)ates from acidic solutions containing high concentrations of chloride ions via a mechanism in which two ligands address the "outer sphere" of the [MCl(4)](2-) unit using both N-H and C-H hydrogen bond donors to form the neutral complex as in 2L + 2HCl + MCl(2) ⇌ [(LH)(2)MCl(4)]. The strengths of L(1)-L(8) as zinc extractants in these pH-dependent equilibria have been shown to be very dependent on the number of amide groups in the R(3-n)N(CH(2)NR'COR″)(n) molecules, anti-intuitively decreasing with the number of strong hydrogen bond donors present and following the order monoamides > diamides > triamides.

Cobalt(III) complexes as functional ligands for metal (oxide) surfaces.

Co(III) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation.

Design and function of pre-organised outer-sphere amidopyridyl extractants for zinc(II) and cobalt(II) chlorometallates: the role of C-H hydrogen bonds.

Four new sterically hindered pyridines, L(1)-L(4)-containing amido substituents at the 2-position act as efficient solvent extractants for [CoCl(4)](2-) or [ZnCl(4)](2-) from acidic chloride solutions through protonation of the pyridino N-centre to form the neutral outer-sphere complexes [(LH)(2)MCl(4)]. These ionophores show very high selectivity for chlorometallate anions over chloride ion and are readily stripped to liberate the free-metal chlorides without the formation of inner-sphere complexes [ML(2)Cl(2)]. Single-crystal X-ray structure determinations of [(L(2)H)(2)CoCl(4)] and [(L(2)H)(2)ZnCl(4)] (L(2) = 2-(4,6-di-tert-butylpyridin-2-yl)-N,N'-dihexylmalonamide) coupled with (1)H NMR spectroscopy and DFT calculations on L(2)H(+) and other complexes of [ZnCl(4)](2-) confirm that the pyridinium NH group does not address the outer co-ordination sphere of the metallanion, but rather forms a hydrogen bond to the pendant amide groups and thus pre-organizes the ligand to present both C-H and amido N-H hydrogen-bond donors to the [MCl(4)](2-) ions.

Piezochromism in nickel salicylaldoximato complexes: tuning crystal-field splitting with high pressure.

The crystal structures of bis(3-fluoro-salicylaldoximato)nickel(II) and bis(3-methoxy-salicylaldoximato)nickel(II) have been determined at room temperature between ambient pressure and approximately 6 GPa. The principal effect of pressure is to reduce intermolecular contact distances. In the fluoro system molecules are stacked, and the Ni⋅⋅⋅Ni distance decreases from 3.

Linking [M(III)3] triangles with "double-headed" phenolic oximes.

Strapping two salicylaldoxime units together with aliphatic α,Ω-aminomethyl links in the 3-position gives ligands which allow the assembly of the polynuclear complexes [Fe(7)O(2)(OH)(6)(H(2)L1)(3)(py)(6)](BF(4))(5)·6H(2)O·14MeOH (1·6H(2)O·14MeOH), [Fe(6)O(OH)(7)(H(2)L2)(3)](BF(4))(3)·4H(2)O·9MeOH (2·4H(2)O·9MeOH) and [Mn(6)O(2)(OH)(2)(H(2)L1)(3)(py)(4)(MeCN)(2)](BF(4))(5)(NO(3))·3MeCN·H(2)O·5py (3·3MeCN·H(2)O·5py). In each case the metallic skeleton of the cluster is based on a trigonal prism in which two [M(III)(3)O] triangles are tethered together via three helically twisted double-headed oximes. The latter are present as H(2)L(2-) in which the oximic and phenolic O-atoms are deprotonated and the amino N-atoms protonated, with the oxime moieties bridging across the edges of the metal triangles.

Structural, magnetic, and electronic properties of phenolic oxime complexes of Cu and Ni.

Square planar complexes of the type Ni(L(1))(2), Ni(L(2))(2), Cu(L(1))(2), and Cu(L(2))(2), where L(1)H = 2-hydroxy-5-t-octylacetophenone oxime and L(2)H = 2-hydroxy-5-n-propylacetophenone oxime, have been prepared and characterized by single-crystal X-ray diffraction, cyclic voltammetry, UV/vis spectroscopy, field-effect-transistor measurements, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, and, in the case of the paramagnetic species, electron paramagnetic resonance (EPR) and magnetic susceptibility. Variation of alkyl groups on the ligand from t-octyl to n-propyl enabled electronic isolation of the complexes in the crystal structures of M(L(1))(2) contrasting with π-stacking interactions for M(L(2))(2) (M = Ni, Cu). This was evidenced by a one-dimensional antiferromagnetic chain for Cu(L(2))(2) but ideal paramagnetic behavior for Cu(L(1))(2) down to 1.

Using the outer coordination sphere to tune the strength of metal extractants.

A series of 3-substituted salicylaldoximes has been used to demonstrate the importance of outer-sphere interactions on the efficacy of solvent extractants that are used to produce approximately one-quarter of the world's copper. The distribution coefficient for extraction of copper by 5-tert-butyl-3-X-salicylaldoximes (X = H, Me, (t)Bu, NO(2), Cl, Br, OMe) varies by more than two orders of magnitude. X-ray structure determinations of preorganized free ligand dimers (10 new structures are reported) indicate that substituents with a hydrogen-bond acceptor atom attached to the 3-carbon atom, ortho to the phenolic oxygen, buttress the intermolecular hydrogen bond from the oximic proton.

Hexa- and octanuclear iron(III) salicylaldoxime clusters.

The syntheses, structures and magnetic properties of six iron complexes stabilised with the derivatised salicylaldoxime ligands Me-saoH(2) (2-hydroxyethanone oxime) and Et-saoH(2) (2-hydroxypropiophenone oxime) are discussed. The four hexanuclear and two octanuclear complexes of formulae [Fe(8)O(2)(OMe)(4)(Me-sao)(6)Br(4)(py)(4)]·2Et(2)O·MeOH (1·2Et(2)O·MeOH), [Fe(8)O(2)(OMe)(3.85)(N(3))(4.

Double loading of ZnCl(2) by polytopic ligands which co-extract Zn(2+) and tetrachloridozincate.

Combining cation- and anion-binding functionalities in a salen-type extractant leads to multiple loading of ZnCl(2). Zn(ii) cations are bound by the salen N(2)O(2)(2-) donor set, and chlorozincate anions are associated with protonated pendant amine groups.

Collision induced dissociation (CID) to probe the outer sphere coordination chemistry of bis-salicylaldoximate complexes.

Ligand-ligand interactions in the outer coordination sphere make an important contribution to the effects of 3-substituents on the stabilities of anionic Cu(II) salicylaldoximato complexes [CuL(L-H)](-). When substituents contain a different number of bonds the interpretation of CID tandem mass spectrometry must take into account the ability of ions to redistribute energy acquired in collisions within different numbers of vibrational modes.

Cation and anion selectivity of zwitterionic salicylaldoxime metal salt extractants.

3-Dialkylaminomethyl substituted salicylaldoximes are efficient metal salt extractants, and, in contrast to related "salen"-based reagents, are sufficiently stable to acid hydrolysis to allow commercial application in base metal recovery. Crystal structures show that metal salts are bound by a zwitterionic form of the reagents, with copper(II) nitrate, tetrafluoroborate and trifluoroacetate forming [Cu()(2)X(2)] assemblies in a tritopic arrangement with a trans-disposition of the anions outwith the coordination sphere. Copper(II) chloride, bromide and zinc(II) chloride form 1:1 assemblies, [Cu()X(2)], with the halides in the inner coordination sphere of the metal, leading to high chloride selectivity and very good mass transport efficiencies of CuCl(2).