Design and Function of Pre‐organised Outer‐Sphere Amidopyridyl Extractants for Zinc(II) and Cobalt(II) Chlorometallates: The Role of CH Hydrogen Bonds

Ellis, Ross J.; Chartres, Jy D.; Henderson, David K.; Cabot, Rafel; Richardson, Patricia; White, Fraser; Schröder, Martin; Turkington, Jennifer R.; Tasker, Peter A.; Sole, Kathryn C.

doi:10.1002/chem.201103616

Cited by 29 publications

(30 citation statements)

References 54 publications

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“…Aliphatic derivatives of b) have been described previously, 11 and those of the type c) are the subject of this paper.…”

Section: Figurementioning

confidence: 99%

“…12 Ensuring that equilibrium (5) is favoured over (8) is a challenging target because this runs counter to the Hofmeister bias in which more highly charged anions, which have higher hydration energies, are expected to be more difficult to extract into low polarity water-immiscible solvents. 13 (8) Earlier work 11,15 has shown that a series of amidopyridines are strong chloridometalate extractants and show a high selectivity for ZnCl 4 2-over Cl -. They are readily stripped without the pyridine nitrogen atom entering the inner coordination sphere of the metal due to the bulky t-butyl substituents in the 6-position ( Figure 1a).…”

Section: Introductionmentioning

confidence: 99%

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Outer-Sphere Coordination Chemistry: Amido-Ammonium Ligands as Highly Selective Tetrachloridozinc(II)ate Extractants

Turkington

Cocalia²,

Kendall

et al. 2012

Inorg. Chem.

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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 ] 2unit 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. Studies of the effects of chloride concentration on extraction have demonstrated that the monoamides in particular show an unusually high selectivity for [ZnCl 4 ] 2over [FeCl 4 ] − and Cl − . Hybrid-DFT calculations on the tri-, di-, and monoamides, L 2 , L 3 , and L 4 , help to rationalize these orders of strength and selectivity. The monoamide L 4 has the most favorable protonation energy because formation of the LH + cation generates a "chelated proton" structure as described above without having to sacrifice an existing intramolecular amide−amide hydrogen bond. The selectivity of extraction of [ZnCl 4 ] 2over Cl − , represented by the process 2[(LH)Cl] + ZnCl 4 2-⇌ [(LH) 2 ZnCl 4 ] + 2Cl − , is most favorable for L 4 because it is less effective at binding chloride as it has fewer highly polar N−H hydrogen bond donor groups to interact with this "hard" anion.

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“…Aliphatic derivatives of b) have been described previously, 11 and those of the type c) are the subject of this paper.…”

Section: Figurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Outer-Sphere Coordination Chemistry: Amido-Ammonium Ligands as Highly Selective Tetrachloridozinc(II)ate Extractants

Turkington

Cocalia²,

Kendall

et al. 2012

Inorg. Chem.

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“…The proligands L1H-L9H and L12H were prepared from the appropriate acetophenones (1-6) by conversion to the diketones (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) and subsequent reaction with hydrazine. Details are provided in the ESI.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2016

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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. 2-nitro-4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L4H) which has a nitro group ortho to the phenolic hydroxyl group unit and has an extraction distribution coefficient for Cu nearly three orders of magnitude higher than its unsubstituted analogue 4-methyl-6-[5-(2,4,4-trimethylpentyl)-1H-pyrazol-3-yl]phenol (L8H). X-ray structure determinations and density functional theory (DFT) calculations confirm that inter-ligand hydrogen bonding between the pyrazole NH group and the phenolate oxygen atom stabilise the Cu-complexes, giving pseudomacrocyclic structures. Electron-accepting groups ortho to the phenol oxygen atoms buttress the inter-ligand H-bonding, enhancing extractant strength but the effectiveness of this is very dependent on steric factors. The correlation between the calculated energies of formation of copper complexes in the gas phase and the observed strength of comparably substituted reagents in solvent extraction experiments is remarkable. Analysis of the energies of formation suggests that big differences in strength of extractants arise principally from a combination of the effects of the substituents on the ease of deprotonation of the proligands and, for the ortho-substituted ligands, their propensity to buttress inter-ligand hydrogen bonding.

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“…Pyridine-amides have been shown to be effective extractants for base metals such as Zn (II) and Co(II) [41,42]. In these systems, the number of amido-substiuents proximate to the pyridine is important to the selectivity of metalate over halide.…”

Section: Ion Pairs and Metalatesmentioning

confidence: 99%

New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

Love¹,

Miguirditchian²,

Chagnes³

2019

Ion Exchange and Solvent Extraction: Volume 23

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1. INTRODUCTION 2. EXTRACTANT DESIGN 2.1. THE ROLE OF COORDINATION CHEMISTRY AND SUPRAMOLECULAR CHEMISTRY ON THE DESIGN OF NEW EXTRACTANTS 2.1.1. COMPLEX FORMATION 2.1.2. ION PAIRS AND METALATES 2.1.3. REVERSE MICELLES 2.1.4. CONCLUSION 2.2. THE ROLE OF PHYSICOCHEMISTRY FOR A RATIONAL DESIGN OF NEW EXTRACTANTS 2.3. CASE STUDIES 2.3.1. DESIGN OF NEW EXTRACTANTS FOR URANIUM RECOVERY FROM WET PHOSPHORIC ACID 2.3.2. CHEMICAL DESIGN IN GOLD RECOVERY BY URBAN MINING 3. FLOWSHEET OPTIMIZATION 3.1. EFFECT OF FLOWRATES ON FLOWSHEET PERFORMANCES 3.2. INFLUENCE OF DEGRADATION ON FLOWSHEET PERFORMANCE 3.3. COMBINING CHEMISTRY AND ENGINEERING FOR FLOWHEET OPTIMIZATION 3.4. PERSPECTIVE IN THE DEVELOPMENT OF TOOLS FOR FLOWSHEET OPTIMIZATION 4. CONCLUSION 5. REFERENCES

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Design and Function of Pre‐organised Outer‐Sphere Amidopyridyl Extractants for Zinc(II) and Cobalt(II) Chlorometallates: The Role of CH Hydrogen Bonds

Cited by 29 publications

References 54 publications

Outer-Sphere Coordination Chemistry: Amido-Ammonium Ligands as Highly Selective Tetrachloridozinc(II)ate Extractants

Outer-Sphere Coordination Chemistry: Amido-Ammonium Ligands as Highly Selective Tetrachloridozinc(II)ate Extractants

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

New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

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