Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Abstract

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M1 + Cat + M2)(+), were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M1 + Cat)(+) and (M2 + Cat)(+) ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li(+), Na(+), and K(+) than the larger ions such as Cs(+) and Rb(+). In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.

Molecular recognition and supramolecular chemistry in the gas phase

“…The first of these studies (Liou & Brodbelt, 1992b) demonstrated a significant size effect for the binding of alkali ions with crown ethers. For example, Li þ binds significantly more strongly to 15-crown-5 than to any other crown.…”

“…From the intensities of the ML and ML' fragments, conclusions can be drawn with respect to the relative binding strengths of the two ligands. This approach was applied to the alkali ion heterodimers with two different crown ether ligands attached to the same central ion (Liou & Brodbelt, 1992b) as well as the complexes of one crown ether with a MM' X þ fragment, where M and M' correspond to two different alkali metal ions and X represents a halogen counter ion (Maleknia & Brodbelt, 1992).…”

Pulsed-field ionization electron spectroscopy and binding energies of alkali metal-dimethyl ether and -dimethoxyethane complexes

“…Brodbelt and co-workers determined the relative alkali ion affinities of crown ethers and acyclic analogs by using kinetic methods. [17][18][19] Again, crown ethers showed higher affinities for specific sizes of metal ions and the size selectivity was more pronounced for the smaller ions. In addition, computational studies have been reported to address the issues of bond energies or enthalpies, [20][21][22][23][24][25][26][27] criteria of optimal structures, [28][29][30] and energy barriers for metal ion migration from one binding site to the other.…”

Photoreactions in the Gas-Phase Complexes of Mg•+−Dioxanes

“…Na + > K + > Cs + . [16][17][18][19] Armentrout's group measured bond dissociation energies (BDEs) of M + (12-crown-4) (M ) Li, Cs), which vary from ∼0.90 eV for Cs + to 3.90 eV for Li + , [20][21][22][23] in good agreement with a theoretical study. 24 Conceptually, dioxanes can be regarded as crown ethers, i.e., 6-crown-2.…”