Journal of Physical Chemistry A, Vol.120, No.36, 7152-7166, 2016
Alkali Cation Chelation in Cold beta-O-4 Tetralignol Complexes
We employ cold ion spectroscopy (UV action and IR-UV double resonance) in the gas phase to unravel the qualitative structural elements of G-type alkali metal cationized (X = Li+, Na+, K+) tetralignol complexes connected by beta-O-4 linkages. The conformation-specific spectroscopy reveals a variety of conformers, each containing distinct infrared spectra in the OH stretching region, building on recent studies of the neutral and alkali metal cationized beta-O-4 dimers. The alkali metal ion is discovered to bind in penta-coordinate pockets to ether and OH groups involving at least two of the three beta-O-4 linkages. Different binding sites are distinguished from one another by the number of M+center dot center dot center dot OH center dot center dot center dot O interactions present in the binding pocket, leading to characteristic IR transitions appearing below 3550 cm(-1). This interaction is mitigated in the major conformer of the K+ adduct, demonstrating a clear impact of the size of the charge center on the three-dimensional structure of the tetramer.