ARE HETEROCYCLIC 2-PI-ELECTRON AROMATIC SYSTEMS HC-GA(H)-CH, M[HGA-C(H)-GAH], [HGA-C(H)-GAH](-), HSI-GA(H)-SIH, M[HGA-SI(H)-GAH] (M = LI, NA, AND K), AND [HGA-SI(H)-GAH](-) STABLE

Ab initio and density functional (BHLYP, B3LYP, and BP86) quantum mech anical methods were applied to predict the structures, properties, and stabilities of HC-Ga(H)-CH, M[H-Ga-C(H)-GaH], [HGa-C(H)-GaH](-), HSi- Ga(H)-SiH, M[HGa-Si(H)-GaH], and [HGa-Si(H)-GaH](-)(M = Li, Na, K) thr ee-membered ring systems. These structures derive from the previously theoretically and experimentally characterized parent homonuclear cycl ogallenes M-2(GaH)(3). Basis sets of triple-zeta plus double polarizat ion augmented with diffuse functions (TZ2P + diffuse) quality were emp loyed at self-consistent field (SCF) and density functional levels of theory. Equilibrium geometries, harmonic vibrational frequencies, and chemical shifts are reported to facilitate experimental verification o f the computed structures. All title compounds are minima and their ge ometries as well as their properties compare well with the cyclogallen e three-membered ring compounds M-2(GaH)(3). Singly charged [HGa- Si(H )-GaH](-) and even neutral HSi-Ga(H)-SiH may well be feasible experime ntal targets. The large negative nucleus independent chemical shifts ( NICS), used as a criterion for aromatic cyclic delocalization, suggest that all title compounds are aromatic.