Year 2005, Month 1 (Section Full Articles, Page 108)
Molecular geometry and electronic structures of stable organic derivatives
of divalent germanium and tin [(Me3Si)2N—M—OCH2CH2NMe2]n
(M = Ge, n = 1; M = Sn, n = 2): a theoretical study
M. S. Nechaev* and Yu. A. Ustynyuk
The molecular geometry and electronic structure of stable organic derivatives of divalent
germanium and tin, [(Me3Si)2N-M-OCH2CH2NMe2]n (M = Ge (4), n = 1; M = Sn (5),
n = 2) and their isomers with broken (4a, 5a) and closed (4b, 5b) intramolecular coordination
bonds M←NMe2, were studied by the density functional (PBE/TZ2P/SBK-JC) and NBO
methods. Factors responsible for stability of their dimers 4c and 5c were established. Dimerization of 5b in the gas phase is a thermodynamically favorable process (∆G 0 = –2.1 kcal mol–1)
while that of 4b is thermally forbidden (∆G 0 = 10.1 kcal mol–1), which is consistent with
experimental data. The M←NMe2 coordination bond energies, ∆E 0, were found to be –5.3
and –8.6 kcal mol–1 for M = Ge and Sn, respectively. NBO analysis showed that the metal
atoms M in molecules 4 and 5 are weakly hybridized. The lone electron pairs of the M atoms
have strong s-character while vacant orbitals of these atoms, LP* M, are represented exclusively by the metal npz-AOs. The strongest orbital interactions between subunits in dimers 4c
and 5c involve electron density donation from the lone electron pairs of oxygen atoms (LP O)
to the LP* M orbitals.
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