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

Abstract

ABSTRACTWe present the results of a combined experimental and computational study of the structures of gas-phase M+(N2O)n (M = Li, Al) complexes. Infrared spectra were recorded in the region of the N2O asymmetric (N = N) stretch using photodissociation spectroscopy employing the inert messenger technique. Unlike in our previous studies on M+(N2O)n (M = Cu, Ag, Au and M = Co, Rh, Ir) complexes, N– and O–bound isomers in this case are near isoenergetic and are not distinguished spectroscopically at this resolution. In the case of Li+ complexes, there is, however, evidence for the presence of bound N2 moieties, indicating the presence of inserted, OLi+N2(N2O)n–type structures. The weak N2 band lies to the blue of the signature of molecularly N– and O–bound ligands and is well–reproduced in the simulated spectra of energetically low-lying structures computed from density functional theory. No such inserted isomers are observed in the case of Al+(N2O)n complexes whose infrared spectra can be understood on the basis of molecularly-bound N2O ligands. The differences in M+(N2O)n structures observed for these closed–shell, ns2, metal centres relative to other metal cations are discussed in terms of the likely bonding motifs.