Facial vs. meridional coordination in gaseous Ni(II)-hexacyclen complexes revealed with infrared ion spectroscopy

We report fingerprint infrared multiple-photon dissociation (IRMPD) spectra of the isolated gaseous hexa-coordinated complex of the macrocycle hexa-aza-18-crown-6 (hexacyclen, 1,4,7,10,13,16-hexaazacyclooctadecane, 18-azacrown-6) with Ni . The metal-ligand complexes are generated using electrospray...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2022-11, Vol.24 (43), p.26890-26897
Main Authors: Munshi, Musleh Uddin, Berden, Giel, Oomens, Jos
Format: Article
Language:English
Subjects:
Chelation
Chemistry
Computation
Cyclotron resonance
Density functional theory
Electron spin
Fourier transforms
Free electron lasers
Gases - chemistry
Infrared lasers
Infrared spectra
Infrared spectroscopy
Ions
Isomers
Ligands
Mass Spectrometry
Protons
Solid phases
Spectrophotometry, Infrared - methods
Spectrum analysis
Vibrational spectra
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Summary:We report fingerprint infrared multiple-photon dissociation (IRMPD) spectra of the isolated gaseous hexa-coordinated complex of the macrocycle hexa-aza-18-crown-6 (hexacyclen, 1,4,7,10,13,16-hexaazacyclooctadecane, 18-azacrown-6) with Ni . The metal-ligand complexes are generated using electrospray ionization (ESI) and IR action spectra are recorded in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR) MS coupled to the infrared free-electron laser FELIX. We investigate geometric structure of the complexes and in particular the chelation motif, by comparison with computed vibrational spectra, obtained using density functional theory (DFT) at the B3LYP/6-31++G(d,p) level. The quasi-octahedral chelation motif of the complex has been well documented in condensed-phase studies, and we focus here on the gas-phase structure, addressing in particular the question of a facial ( ) a ( ) octahedral chelation geometry. Based on the good agreement between calculated linear IR spectra and experimental IRMPD spectra, we conclude that the gas-phase complex adopts a chelation geometry and we exclude significant contribution of the isomer, which is computed to lie about 10 kJ mol higher in energy. We also address the possible presence of both meridional diastereomers and of higher energy conformers of meridional isomers. Finally, as expected for the d Ni -ion in an octahedral ligand environment, the IR spectrum also shows that the complexes are in a high-spin electron configuration.
ISSN:1463-9076
1463-9084
DOI:10.1039/d2cp03871d