The combination of boron and carbon elements with rare earth metals leads to the formation of materials having interestingphysical and structural properties. In theses compounds of formula MxByCz, The non-metal atoms form either two-dimensionalnetworks, or mon-dimensional zig-zag chains, or finite linear units of various length. The dimensionality of boron-carbonsublattice is related to the average valence electron count (VEC) per light atom (B or C). The bonding properties of rare earthmetal boron carbide compounds are analysed by means of extend Hückel tight-binding calculations. Results indicate that thesecompounds can be described in first approximation as being built of anionic units interacting with not fully oxidized metalliccations
