PECULIAR STRUCTURES OF SMALL MAGNESIUM CARBIDE CLUSTERS - MGC2, (MGC2)(2), AND (MGC2)(4)

The geometries of MgC2, (MgC2)(2), and (MgC2)(4) in their ground and l ow-lying excited electronic states have been determined via ab initio electronic structure methods with flexible basis sets and using variou s approaches for treating electron correlation. We find these species to involve primarily ionic bonding and to be very thermodynamically st able. We find the C-2(2-) moiety to exhibit both 1- and 2-fold coordin ation to the Mg2+ sites in the two larger clusters, which is reminisce nt of what is seen in transition metal met-car compounds.