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The use of electrospray mass spectrometry to determine speciation in a dynamic combinatorial library for anion recognition.

Phillips HI, Chernikov AV, Fletcher NC, Ashcroft AE, Ault JR, Filby MH, Wilson AJ - Chemistry (2012)

Bottom Line: The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24 h.Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide-functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group.Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI-MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry and Chemical Engineering, Queen's University Belfast, UK.

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Normalized intensities obtained for FeX2/L1 L3, determined after 24 h for {[Fe(L1/L3)3]X}+ and [Fe(L1/L3)3]2+. [Fe(L1)3] (blue), [Fe(L1)2(L3)] (orange), [Fe(L1)(L3)2] (green) and [Fe(L3)3] (red).
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fig05: Normalized intensities obtained for FeX2/L1 L3, determined after 24 h for {[Fe(L1/L3)3]X}+ and [Fe(L1/L3)3]2+. [Fe(L1)3] (blue), [Fe(L1)2(L3)] (orange), [Fe(L1)(L3)2] (green) and [Fe(L3)3] (red).

Mentions: Comparison of the final distribution of the four complexes observed in the mass spectrum with the four salts tested after 24 h indicates that for the divalent species [Fe(L)3]2+, the counteranion does not significantly affect the speciation (Figure 5), which approaches the expected statistical polynomial distribution (1:3:3:1) of the four species (with a slight preference for ligand L1 over L3 as previously observed). A remarkably similar distribution was also observed in the monovalent species containing either perchlorate or tetrafluoroborates ions. However, in the presence of simple halide ions, the preference for L1 over L3 in the complex {[Fe(L1)3]X}2+ (in which X is Cl or Br) is further exaggerated giving an indication that a bound anion can determine the product distribution. Hence, the anion is not only involved in the rate at which the system reaches equilibrium, but significantly, it is also involved in determining the equilibrium, as would be anticipated if these anions are “binding” to the amide ligand systems.


The use of electrospray mass spectrometry to determine speciation in a dynamic combinatorial library for anion recognition.

Phillips HI, Chernikov AV, Fletcher NC, Ashcroft AE, Ault JR, Filby MH, Wilson AJ - Chemistry (2012)

Normalized intensities obtained for FeX2/L1 L3, determined after 24 h for {[Fe(L1/L3)3]X}+ and [Fe(L1/L3)3]2+. [Fe(L1)3] (blue), [Fe(L1)2(L3)] (orange), [Fe(L1)(L3)2] (green) and [Fe(L3)3] (red).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3569615&req=5

fig05: Normalized intensities obtained for FeX2/L1 L3, determined after 24 h for {[Fe(L1/L3)3]X}+ and [Fe(L1/L3)3]2+. [Fe(L1)3] (blue), [Fe(L1)2(L3)] (orange), [Fe(L1)(L3)2] (green) and [Fe(L3)3] (red).
Mentions: Comparison of the final distribution of the four complexes observed in the mass spectrum with the four salts tested after 24 h indicates that for the divalent species [Fe(L)3]2+, the counteranion does not significantly affect the speciation (Figure 5), which approaches the expected statistical polynomial distribution (1:3:3:1) of the four species (with a slight preference for ligand L1 over L3 as previously observed). A remarkably similar distribution was also observed in the monovalent species containing either perchlorate or tetrafluoroborates ions. However, in the presence of simple halide ions, the preference for L1 over L3 in the complex {[Fe(L1)3]X}2+ (in which X is Cl or Br) is further exaggerated giving an indication that a bound anion can determine the product distribution. Hence, the anion is not only involved in the rate at which the system reaches equilibrium, but significantly, it is also involved in determining the equilibrium, as would be anticipated if these anions are “binding” to the amide ligand systems.

Bottom Line: The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24 h.Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide-functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group.Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI-MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry and Chemical Engineering, Queen's University Belfast, UK.

Show MeSH