Metal Atom Dynamics in Superbulky Metallocenes: A Comparison of (CpBIG)2Sn and (CpBIG)2Eu

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• 作者：Sjoerd Harder ; Dominik Naglav ; Peter Schwerdtfeger ; Israel Nowik ; Rolfe H. Herber
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：February 17, 2014
• 年：2014
• 卷：53
• 期：4
• 页码：2188-2194
• 全文大小：326K
• ISSN：1520-510X

文摘

Cp^BIG₂Sn (Cp^BIG = (4-n-Bu-C₆H₄)₅cyclopentadienyl), prepared by reaction of 2 equiv of Cp^BIGNa with SnCl₂, crystallized isomorphous to other known metallocenes with this ligand (Ca, Sr, Ba, Sm, Eu, Yb). Similarly, it shows perfect linearity, C鈥揌路路路C(蟺) bonding between the Cp^BIG rings and out-of-plane bending of the aryl substituents toward the metal. Whereas all other Cp^BIG₂M complexes show large disorder in the metal position, the Sn atom in Cp^BIG₂Sn is perfectly ordered. In contrast, ¹¹⁹Sn and ¹⁵¹Eu M枚脽bauer investigations on the corresponding Cp^BIG₂M 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 Cp^BIG₂M 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 Cp_center鈥揗鈥揅p_center 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鈥揔roll CCSD(T) level was extended with values (atomic units) for Sn²⁺ 15.35, Sm²⁺(4f^{6 7}F) 9.82, Eu²⁺(4f^{7 8}S) 8.99, and Yb²⁺(4f^{14 1}S) 6.55. This polarizability model cannot be applied to predominantly covalently bound Cp^BIG₂Sn, which shows a perfectly ordered structure. The bent geometry of Cp*₂Sn should therefore not be explained by metal polarizability but is due to van der Waals Cp*路路路Cp* attraction and (to some extent) to a small p-character component in the Sn lone pair.