Infrared Spectroscopy of Gas-Phase M+(CO2)n (M = Co, Rh, Ir) Ion-Molecule Complexes.

Andreas Iskra,Stuart R Mackenzie,Alastair P Sharp,Michael J Kent,Alexander S Gentleman,Aras Kartouzian

doi:10.1021/acs.jpca.6b10902

Andreas Iskra, Stuart R Mackenzie + Show 4 more

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https://doi.org/10.1021/acs.jpca.6b10902

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Abstract

The structures of gas-phase M+(CO2)n (M = Co, Rh, Ir; n = 2-15) ion-molecule complexes have been investigated using a combination of infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy and density functional theory. The results provide insight into fundamental metal ion-CO2 interactions, highlighting the trends with increasing ligand number and with different group 9 ions. Spectra have been recorded in the region of the CO2 asymmetric stretch around 2350 cm-1 using the inert messenger technique and their interpretation has been aided by comparison with simulated infrared spectra of calculated low-energy isomeric structures. All vibrational bands in the smaller complexes are blue-shifted relative to the asymmetric stretch in free CO2, consistent with direct binding to the metal center dominated by charge-quadrupole interactions. For all three metal ions, a core [M+(CO2)2] structure is identified to which subsequent ligands are less strongly bound. No evidence is observed in this size regime for complete activation or insertion reactions.

Highlights

There has been much interest in activation in synthetic chemistry over carbon the past tdwiooxdideecad(eCsO.1−2)[3]Most practical CnTOdh−2isinawsseyermatkimoennetinrriegcaocstftirotehnteschCleOvaidb2irnbagotinotdonaelinnhfsreaernqtceuedesnOtchyCe oact−h(a2Cn3cO4e9)s (CO2) transformations involve metal-based catalysts, and detailed investigations are required to better understand the fundamental interactions involved
The structures of gas-phase M+(CO2)n (M = Co, Rh, Ir; n = 2−15) ion− molecule complexes have been investigated using a combination of infrared resonanceenhanced photodissociation (IR-REPD) spectroscopy and density functional theory
All vibrational bands in the smaller complexes are blue-shifted relative to the asymmetric stretch in free CO2, consistent with direct binding to the metal center dominated by charge−quadrupole interactions

Summary

INTRODUCTION

There has been much interest in activation in synthetic chemistry over carbon the past tdwiooxdideecad(eCsO.1−2)[3]. For the smaller complexes (n ≤ 10), the inert messenger or “rare gas tagging”[32−36] technique has been employed whereby loss of a weakly−bound argon atom provides a mass spectrometric signature of photon absorption This technique has been exploited previously by our group in studies of larger naked and decorated transition metal clusters.[37−43] For the larger M+(CO2)n complexes (n > 10), the intensity of the Ar-tagged species is too low and depletion of the M+(CO2)n complex is monitored by CO2 loss directly. Where it is possible to record naked and Ar-tagged complexes simultaneously, in most cases we observe no qualitative difference in the spectra of the two, lending support to the proposition that the argon tag is inert and does not significantly perturb the cluster structure

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES