abstract
- We present cryogenic ion vibrational spectroscopy of complexes of the anion receptor octamethyl calix[4]pyrrole (omC4P) with nitrate in vacuo. We compare the resulting vibrational spectrum with that in deuterated acetonitrile solution, and we interpret the results using density functional theory. Nitrate binds to omC4P through hydrogen bonds between the four NH groups of the receptor and a single NO group of the nitrate ion. The shape of the ion breaks the C4v symmetry of the receptor, and this symmetry lowering is encoded in the pattern of the NH stretching modes of omC4P. We compare the spectrum of nitrate-omC4P with that of chloride-omC4P to discuss effects of ion size, shape, and solvent interaction on the ion binding behavior.