Supramolecular assemblies from ditopic ligands and transition metal salts †

Miller, Hamish A.; Laing, Norman; Parsons, Simon; Parkin, Andrew; Tasker, Peter A.; White, David J.

doi:10.1039/b003436n

Cited by 42 publications

(27 citation statements)

References 28 publications

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“…Supramolecular assemblies have also been found for metal sulfate complexes of salen ligands bearing just simple tertiary amine groups, [7,26,27,37] the four SO 4 2À oxygen atoms are disordered over two partially occupied sites; this results in two hydrogen-bonding interactions, one from N2ÀH2a to O2S (65 % occupancy), the second to O2T (35 % occupancy). All other oxygen atoms of the SO 4 2À and other hydrogen-bond donor and acceptor atoms, including the amide, phenolate and second piperazinium groups are involved in an extensive hydrogen-bonding network with the lattice water and methanol molecules (see Supporting Information Table S3).…”

Section: Resultsmentioning

confidence: 95%

“…[24] We report herein the incorporation of amide and urea groups into the zwitterionic ditopic ligand framework of bissalicylaldimine (salen-type) ligands. [25][26][27][28][29] It was anticipated that the presence of hydrogen-bond donors in the target ionophores L n (n = 1-8; Scheme 1) would aid these derivatives to address the solvation spheres of complexed anions and hence influence the observed selectivity towards anion transport.…”

Section: Introductionmentioning

confidence: 99%

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Anion Selectivity in Zwitterionic Amide‐Functionalised Metal Salt Extractants

Galbraith

Wang

et al. 2007

Chemistry A European J

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Amide-functionalised salen ligands capable of extracting metal salts have been synthesised and characterised. Single-crystal X-ray structure determinations of complexes of NiSO4, [Ni(L)(SO4)], confirm that the ionophores are in a zwitterionic form with Ni(II) bound in the deprotonated salen moiety and the SO4(2-) ion associated with protonated pendant N'-amidopiperazine groups. Treatment of [Ni(L)(SO4)] with base removes the protons from the pendant amido-amine group resulting in loss of the SO4(2-) ion and formation of metal-only complexes of type [Ni(L-2H)], which have been characterized by single-crystal X-ray diffraction. Three of the ligands with solubilities suitable for solvent extraction studies show loading and stripping pH-profiles that are suitable for the recovery of CuSO4 or CuCl2 from industrial leach solutions. The copper-only complexes, [Cu(L-2H)], are selective for Cl- over SO4(2-) in both solvent extraction and bulk liquid membrane transport experiments and were found to bind Cl- in two steps via the formation of a 1:1:1 [Cu(L-H)Cl] assembly, followed by a 1:1:2 [Cu(L)Cl2] assembly as the pH of the aqueous phase is lowered. The anion transport selectivity was evaluated for a number of other mono-charged anions and interestingly the ligands were found to display a preference for the Br- ion. To probe the influence of the Hofmeister bias on the selectivity of anion complexation, single-phase potentiometric titration experiments were employed to investigate the binding of SO4(2-) and Cl- by one of the copper only complexes, [Cu(L-2H)] in 95 %/5 % MeOH/water. Under these conditions selectivity was reversed (SO4(2-)>Cl-) confirming that the Hofmeister bias, which reflects the relative hydration energies of the anions, dominates the selectivity of anion extraction from aqueous media into CHCl3.

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Section: Resultsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Anion Selectivity in Zwitterionic Amide‐Functionalised Metal Salt Extractants

Galbraith

Wang

et al. 2007

Chemistry A European J

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“…This intuitively plausible concept rests, however, on ambiguous evidence, which does not allow a clear-cut assessment of true cooperativity. In fact, the current literature on binding of ion pairs to ditopic receptors is essentially based on 1) crystallographic evidence, [3][4][5][6][7][8][9][10][11] which demonstrates the existence of ion-pair complexes but not of cooperative effects, 2) transport through membranes [7,[12][13][14][15] or extraction from aqueous solutions, [4,[16][17][18][19][20][21] which is not necessarily or solely dependent on cooperativity, and 3) binding measurements in solution, [5,6,10,11,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] which suffer from a number of inconsistencies that do not allow a convincing and unambiguous assessment of cooperativity. This drawback is caused by the common practice of comparing the association constant of an ion pair with a ditopic ...…”

Section: Introductionmentioning

confidence: 99%

Ion‐Pair Binding: Is Binding Both Binding Better?

Roelens

Vacca

Francesconi

et al. 2009

Chemistry A European J

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It is often tempting to explain chemical phenomena on the basis of intuitive principles, but this practice can frequently lead to biased analysis of data and incorrect conclusions. One such intuitive principle is brought into play in the binding of salts by synthetic receptors. Following the heuristic concept that "binding both is binding better", it is widely believed that ditopic receptors capable of binding both ionic partners of a salt are more effective than monotopic receptors because of a cooperative effect. Using a newly designed ditopic receptor and a generalized binding descriptor, we show here that, when the problem is correctly formulated and the appropriate algorithm is derived, the cooperativity principle is neither general nor predictable, and that competition between ion binding and ion pairing may even lead to inhibition rather than enhancement of the binding of an ion to a ditopic receptor.

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“…Transition metal complexes of multidentate Schiff base ligands find application as model analogs of certain metal enzymes [4], catalysts in oxidative addition reactions [5][6][7][8][9], and modifiers for selective electrodes, as well as through different uses in material chemistry [10][11][12]. A bimetallic core is versatile at the active site of many metalloenzymes and plays an essential role in biological systems via the interplay of a pair of metal ions [13].…”

Section: Introductionmentioning

confidence: 99%