稀土夹心化合物的SCF-Xａ-SW研究 2:Cp~2Yb C~2H~2和Cp~2Yb(OC)~2

用SCF-Xａ-SW方法非相对论和相对论方案计算了Cp~aYb C~2H~2和Cp~2Yb(OC)~2.非相对论主HOMO是Cp的π轨道,相对论间接效应的作用,使得Yb的4f轨道能级上升为HOMO,相对论结果与Yb二价化合物不稳定、易氧化的实验结果一致,也表明了研究重稀土化合物考虑相对论效应的必要性.计算共价键强度与Cp~2Yb相近,比YbF~3和Cp~3SM弱,再次表明二价稀土化合共价键比三价化合物弱.同时也证实了σ型配体(CO)与稀土元素的配 位作用比π型配体(C~2H~2)强的结论.

SCF-Xａ-SW calculations on lanthanide metallocenes.pt,2: Cp~aYb C~2H~2 and Cp~2Yb(OC)~2

SCF-Xa-SW calcns. are carried out on Cp2YbC2H2 and Cp2Yb(OC)2, both of the nonrelativistic and relativistic schemes have been tried. Discussing orbital interactions from energy sequences, contour maps and populations, a weak interaction between C2H2 and Yb is shown, which is in agreement with experiments CO interacts with Yb more strongly than C2H2 does, namely, coordinating effect of s ligand is stronger than that of p one. There are some stronger covalent bonds in Cp2Yb(OC)2 than those in Cp2YbC2H2, but both of their bonds are less covalent in character than those in three valence Ln compounds such as Cp2Sm and LnF3. Ln components for bonding orbitals are in the order: d>f>p>s. HOMO are Cpp orbital for nonrelativistic calcns., but Ln 4f one for relativistic treats due to relativistic indirect effect makes Ln4f level rise up, which is consistent with the experimental result that the two valence Ln compounds are unstable and easily oxidized.