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 micros later, shows that the nominally hypervalent complexes LiXCH2 (X=O or NH) are stable, residing in potential energy minima. In the time span between the neutralization and reionization events, the LiXCH2 molecules dissociate partly into their constituents, Li + XCH2, the fragmentation extent of LiNHCH2 being more extensive. Ab initio calculations reveal three bound states for both Li atom complexes. Two (states A and B) resemble C-centered radicals carrying an ion pair, Li+*(-)X-CH2*, and can be viewed as lithiated derivatives of the hydroxymethyl (HOCH2*) or aminomethyl (H2NCH2*) radical; the third state (C) represents a conventional, 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 true for LiNHCH2, where C is the most stable arrangement and B only marginally bound. The larger degree of dissociation observed for LiNHCH2 vis à vis LiOCH2 upon neutralization-reionization points out that the experiment samples a considerable amount of state B which is barely bound for LiNHCH2.