Spectroscopic Investigation of the Gas-Phase Conformations of 15-Crown-5 Ether Complexes with K⁺

Abstract

Infrared multiple photon dissociation action spectra of the binary and ternary gas-phase complexes formed by 15-crown-5 ether with potassium cations (15c5-K + and 15c5-K + -15c5) are reported. The spectra span the 800-1500 cm -1 infrared range. Particularly significant differences are found in the position and structure of the CO-stretching band of the two types of complexes. The computational prediction at the DFT-B3LYP/ 6-31G* level of theory agrees well with the experimental observations, and provides a correlation between the spectral differences and the structural changes associated with the coordination of the ether oxygens with the alkali cation. The 15c5-K + complex adopts a pyramidal structure, with the cation lying above the center of mass of the ether ring at a distance similar to its ionic radius. The ternary 15c5-K + -15c5 complex features a less tight coordination of the cation and a relative rotation between the backbones of the two crown ethers, which minimizes the intermolecular repulsions between the oxygens.

IRPD spectroscopy and ensemble measurements: Effects of different data acquisition and analysis methods

“…IRPD spectra of hydrated La 3ϩ (H 2 O) 36 and La 3ϩ (H 2 O) [35][36][37] were acquired using a 2.75 Tesla Fourier transform ion cyclotron resonance mass spectrometer coupled to a tunable OPO/OPA laser system [4]. These hydrated ions are formed by nanoelectrospray ionization using borosilicate capillaries that are pulled to an i.d.…”

“…Exposure of La 3ϩ (H 2 O) 36 to the 133 K blackbody field of the ion cell results in ϳ16% dissociation after 1.5 s (Figure 2, top middle). Irradiating these ions with 3694 cm Ϫ1 light for this same time period results in loss of up to four water molecules, corresponding to ϳ77% dissociation due to BIRD and laser irradiation (Figure 2, top right).…”

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Three different commonly used infrared photodissociation (IRPD) spectroscopy acquisition and analysis methods are described, and results from these methods are compared using the same dataset for an extensively hydrated metal cation, La 3ϩ (H 2 O) 36 . Using the first-order laser-induced photodissociation rate constant as an IRPD intensity has several advantages over photodissociation yield and depletion/appearance methods in that intensities can be more directly compared with calculated infrared absorption spectra, and the intensities can be readily corrected for changes in laser power or irradiation times used for optimum data acquisition at each frequency.

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“…Because the PDY depends on a ratio of correlated abundances, it does not depend on fluctuations in initial precursor population from scan to scan. This is the method currently used for the majority of IRPD spectra obtained using FELIX [31,32,[35][36][37][38][39][40], including many tightly-bound complexes for which the absorption of many mid-infrared photons is typically necessary to induce fragmentation. An action spectrum can also be obtained by measuring the extent of depletion of the precursor ion or appearance of a fragment ion.…”

Theoretical Study on 15-Crown-5 Complex With Some Metal Cations

“…Theoretical studies of the crown ether complexes with a single alkali cation (Li have been conducted by Hill et al [10][11], Hag-Sung Kim [12], Martınez-Haya et al [13], Yoshiya et al [14] and Hwan Jin Kim et al [15]. The agreement between theory and collision-induced dissociation (CID) experimental cations binding enthalpies are generally good, but the differences as much as 14 kcal/mole were noted for 12-crown-4 complexes with some of the heavier cations [10].…”