|Title||Tweezer-like Complexes of Crown Ethers with Divalent Metals: Probing Cation-Size-Dependent Conformations by Vibrational Spectroscopy in the Gas Phase|
|Publication Type||Journal Article|
|Year of Publication||2012|
|Authors||F. Gamez, P. Hurtado, S. Hamad, B. Martinez-Haya, G. Berden, J. Oomens|
|Type of Article||Article|
|Keywords||12-CROWN-4, 18-CROWN-6, ALKALINE-EARTH CATIONS, BINDING, BIS(CROWN ETHER), crown ethers, density functional calculations, divalent metals, infrared, INFRARED-SPECTROSCOPY, IONS, MOLECULAR RECOGNITION, MOLECULAR-TWEEZERS, MULTIDENTATE LIGANDS, RECOGNITION, SPECTROSCOPY|
Crown ethers constitute central building blocks for the synthesis of molecular tweezers capable of trapping cationic species. In this study, isolated ternary complexes comprising two crown-6 (18c6) ether molecules and one divalent cation of varying size (Cu2+, Ca2+, Ba2+) are investigated by means of laser vibrational action spectroscopy and computations. In the ternary (18c6)(2)-Cu2+ complex, one of the crown units folds tightly around the cation, while the second crown ether unit binds peripherally. Such asymmetrical binding manifests itself as a bimodal splitting of the vibrational bands measured for the complex. The size of the cation in the Ca2+ and Ba2+ complexes leads to a progressively more symmetrical coordination of the two crown ether molecules with the metal. In particular, in the spectrum of the (18c6)(2)-Ba2+ complex, the two components of the vibrational bands are merged into single-maximum envelopes. This is consistent with a C-2 arrangement predicted by the computation, in which the cation coordinates with the two crown ether units in a fully symmetrical way.
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