Crown Ether - Alkali Complexes Questioning the Best-fit Model

1 Crown Ether - Alkali Complexes Questioning the Best-fit Model 

The results of these measurements are affinity ladders, in which a qualitative trend of binding affinities can be observed. Because of the temperature problem these values are only relative data and conversion into absolute data is not easily possible. 

Another method is the measurement of equilibrium constants that can be performed in a FT-ICR mass spectrometer [59]. One example is an examination of a complex CiM consisting of crown ether Ci and a metal cation M that is reacted with a mixture of Ci and a second neutral crown ether C2 (both present with the same concentration) until the reaction has reached the equilibrium state. The intensity ratio of the two complexes CiM+ and C2M+ directly reflects the binding strengths of the crown ether to the metal cation. 

Binding energies (in eV) of crown ethers and simple analogues (DME = dimethyl ether, DXE = dimethoxy ethane) to alkali metal ions. Each value refers to the binding energy of one ligand (e.g. 

4 DME means the binding energy of the 4th DME ligand, when already three are present in the complex). Eor comparison, also the sums of the BDE s of two and four DME and two DXE ligands are given. All data taken from ref. [60]. 

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