SCF-Xa-SW calcns. are carried out on lanthanide bridged metallocenes (Cp2YbCl)2 and (Cp2ErH)2; both nonrelativistic and relativistic schemes were tried. The bonds of (Cp2YbCl)2 and (Cp2ErH)2 are more covalent in character than those of Cp2Yb and Cp2YbC2H2 but similar to those of Cp3Sm and LnF3. Three valent Ln compounds are more covalent in character than two valent. The covalent bonding of (Cp2ErH)2 with a H bridge is stronger than that of (Cp2YbCl)2 with a Cl bridge. There are some obvious differences in energy level sequences, valent orbital compns. and bonding pictures between the two schemes, which reveals that the relativistic scheme is necessary to obtain reliable results for heavy lanthanide compounds

Key words: CHEMICAL BONDS, ELECTRONIC STRUCTURE, METALLOCENES, YTTERBIUM COMPLEX, CYCLOPENTENE P, SANDWICH COMPOUNDS, ERBIUM COMPLEX