(Cp2Sn)-Sn-BIG (Cp-BIG = (4-n-Bu-C6H4)(5)cyclopentadienyl), prepared by reaction of 2 equiv of (CpNa)-Na-BIG with SnCl2, crystallized isomorphous to other known metallocenes with this ligand (Ca, Sr, Ba, Sm, Eu, Yb). Similarly, it shows perfect linearity, C-H center dot center dot center dot C(pi) bonding between the Cp-BIG rings and out-of-plane bending of the aryl substituents toward the metal. Whereas all other (Cp2M)-M-BIG complexes show large disorder in the metal position, the Sn atom in (Cp2Sn)-Sn-BIG is perfectly ordered. In contrast, Sn-119 and Eu-151 Mossbauer investigations on the corresponding (Cp2M)-M-BIG metallocenes show that Sn(II) is more dynamic and loosely bound than Eu(II). The large displacement factors in the group 2 and especially in the lanthanide(II) metallocenes (Cp2M)-M-BIG can be explained by static metal disorder in a plane parallel to the Cp-BIG rings. Despite parallel Cp-BIG rings, these metallocenes have a nonlinear CDcenter-M-CPcenter geometry. This is explained by an ionic model in which metal atoms are polarized by the negatively charged Cp rings. The extent of nonlinearity is in line with trends found in M2+ ion polarizabilities. The range of known calculated dipole polarizabilities at the Douglas-Kroll CCSD(T) level was extended with values (atomic units) for Sn2+ 15.35, Sm2+(4f(67)F) 9.82, Eu2+(4f(7) S-8) 8.99, and Yb2+(4f(14) S-1)) 6.55. This polarizability model cannot be applied to predominantly covalently bound (Cp2Sn)-Sn-BIG, which shows a perfectly ordered structure. The bent geometry of Cp*Sn-2 should therefore not be explained by metal polarizability but is due to van der Waals Cp*center dot center dot center dot Cp* attraction and (to some extent) to a small p-character component in the Sn lone pair.
- EFFECTIVE IONIC-RADII
- ALKALINE-EARTH METALS
- X-RAY CRYSTAL
- BIS(PENTAMETHYLCYCLOPENTADIENYL) COMPLEXES
- CRYSTALLOGRAPHIC CHARACTERIZATION