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Abstract
We investigate the binding motifs of host-guest complexes of the anion receptor octamethyl calix[4]pyrrole (omC4P) with the formate anion using cryogenic ion vibrational spectroscopy in concert with density functional theory. The resulting IR spectrum in vacuo is compared to that in deuterated acetonitrile and acetone solutions. The formate-omC4P complex has three low energy isomers in vacuo:(i) one with an oxygen atom of formate interacting with three of the NH groups of omC4P and the other oxygen atom interacting with the remaining NH group; (ii) one with a single oxygen atom of formate interacting with all four NH groups of omC4P; and (iii) one with each oxygen atom interacting with two NH groups. Each complex geometry lowers the C4v symmetry of the receptor to C1, Cs, or C2v, respectively, and this symmetry breaking and isomerism is reflected in the broadening and pattern of the NH stretching modes of omC4P.
Supplementary materials
Title
Supporting Information, Part 1
Description
Experimental IR photodissociation spectrum of HCOO−omC4P compared to the scaled harmonic calculations of isomer A and isomer B; estimated energy barriers between isomer A and isomers B and C; ; mode patterns of NH stretching vibrational modes; atomic coordinates for neutral omC4P and for HCOO−omC4P.
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Title
Supporting Information, Part 2
Description
Animation of the NH stretching mode with anharmonic behavior in isomer A and isomer B.
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