Structural isomers and low-lying electronic states of gas-phase M⁺(N₂O)_n (M = Co, Rh, Ir) ion–molecule complexes

Abstract

The structures of gas-phase group nine cation–nitrous oxide metal–ligand complexes, M+(N2O)n (M = Co, Rh, Ir; n = 2–7) have been determined by a combination of infrared photodissociation spectroscopy and density functional theory.

Infrared spectroscopy of closed s-shell gas-phase M+(N2O)n (M = Li, Al) ion-molecule complexes

“…The O-bound and N-bound minima are separated by a large barrier to internal rotation of > 0.8 eV with the zero-point energy of the T-shaped (90) structure very close to the dissociation energy (i.e., barely bound). As observed in our previous studies of M + (N2O)n complexes, [35,36] the rapid cooling which occurs within our free-jet expansion facilitates the trapping of excited isomeric forms behind such barriers, leading to the possibility of a range of isomers with mixed N-and Obound ligands. In most of our previous studies, however, (for Cu + , Ag + , Au + and Co + , Rh + and Ir + ) the N-bound potential minimum is significantly deeper than the O-bound giving rise to a clearly resolved spectral signature of each.…”

“…The instrument and technique employed in these studies have been described in detail in previous publications, so only brief details are given here here. [35,36,40] Gas-phase M + (N2O)n (M = Li, Al)…”

“…The evolution of the Li + (N2O)n-Ar spectra with n exhibits marked similarity with that for the Co + (N2O)n-Ar and coinage metal M + (N2O)n-Ar (M = Cu, Ag, Au) complexes and a similar rationale can be applied to their understanding. [36] , [35] First, it is informative to understand the binding of the Li + N2O complex. The barrier between the two minima is extremely small and we expect a quasi-linear structure experiencing wide-amplitude motion (up to  50) in this coordinate.…”

“…In what follows, we adopt a notation 2S+1 M + N x O y for a particular structure in which Unlike the group nine [36] and coinage metal complexes, [35] in which the spectral signatures of N-and O-bound ligands were well-resolved (separated by 118 cm -1 in the case of Au + (N2O)2-Ar) in the case of Li + (N2O)n-Ar complexes the two lie very close in wavenumber. This reflects the almost isoenergetic nature of the 1 Li + N 2 , 1 Li + N 1 O 1 and 1 Li + O 2 structures.…”

“…[34] This group has recently reported spectroscopic studies of coinage metal and group 9 cation M + (N2O)n complexes, combining infrared photodissociation (IRPD) spectroscopy with quantum chemical calculations to identify structural binding motifs. [35,36] In both cases spectroscopicallydistinct N-and O-bound ligands were identified, giving rise to a diverse range of structural isomers.…”