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Tweezer‐like Complexes of Crown Ethers with Divalent Metals: Probing Cation‐Size‐Dependent Conformations by Vibrational Spectroscopy in the Gas Phase
Author(s) -
Gámez Francisco,
Hurtado Paola,
Hamad Said,
MartínezHaya Bruno,
Berden Giel,
Oomens Jos
Publication year - 2012
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201100044
Subject(s) - crown ether , chemistry , molecular tweezers , divalent , crystallography , molecule , spectroscopy , ternary operation , cationic polymerization , stereochemistry , supramolecular chemistry , crystal structure , organic chemistry , ion , physics , quantum mechanics , computer science , programming language
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 [18]crown‐6 (18c6) ether molecules and one divalent cation of varying size (Cu 2+ , Ca 2+ , Ba 2+ ) are investigated by means of laser vibrational action spectroscopy and computations. In the ternary (18c6) 2 –Cu 2+ 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 Ca 2+ and Ba 2+ 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 –Ba 2+ 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.