The electronic structure of two novel carbides, Ca3Cl2C3 and Sc3C4, containing C3 units

The triatomic C3 unit that is known to exist in Mg2C3 has recently been found in the new compounds Ca3Cl2C3 and Sc3C4. The electronic structure of these compounds is analyzed with the aid of extended Hückel Calculation. A fragment molecular Orbital analysis (FMO) is used to study the bonding characteristic of the C3 unit in the ionic Ca3Cl2C3, and in Sc3C4, the latter Containing C2 unit and single C atoms as well. Sc3C4 Contain partially filled Sc (d) and C2 bands leading to Metallic conductivity and Pauli Paramagnetism. The CC bond distance in the diatomic C2 units is significantly increased (dcc= 125 pm) relative to C2−2 or acetylene, because antibonding π*g orbitals are partially filled. The unusual bending of the C3 unit (dcc= 134 pm) in Sc3C4 (175,8°) and in Ca3Cl2C3 (169,0°) is likely to be a result of the packing arrangement in these structures.