Complexes of Li atoms with formaldehyde (LiOCH2) and formaldimine (LiNHCH2): Stability via electrostatic and charge transfer interactions

The Li atom adducts of formaldehyde (LiOCH2) and formaldimine (LiNHCH2) are produced in the gas phase by neutralization of the corresponding cations. Subsequent reionization, ca. 0.3 mus later, shows that the nominally hyperv alent complexes LiXCH2 (X=O or NH) are stable, residing in potential energy minima. In the time span between the neutralization and reionization event s, the LiXCH2 molecules dissociate partly into their constituents, Li + XCH 2, the fragmentation extent of LiNHCH2 being more extensive. Ab initio calc ulations reveal three bound states for both Li atom complexes. Two (states A and B) resemble C-centered radicals carrying an ion pair, Li+.-X-CH.(2), and can be viewed as lithiated derivatives of the hydroxymethyl (HOCH2.) or aminomethyl (H2NCH2.) radical; the third state (C) represents a convention al, electrostatically bonded Li-X=CH2 complex with an essentially intact X- C double bond and the unpaired electron located at the metal atom. States A and B are bound more strongly than state C for LiOCH2; the opposite is tru e for LiNHCH2, where C is the most stable arrangement and B only marginally bound. The larger degree of dissociation observed for LiNHCH2 vis a vis Li OCH2 upon neutralization-reionization points out that the experiment sample s a considerable amount of state B which is barely (C) 2001 American Societ y for Mass Spectrometry.