Molecular geometry and electronic structures of stable organic derivatives of divalent germanium and tin $$[(\operatorname{Me} _3 \operatorname{Si} )_2 \operatorname{N} {\kern 1pt} ---{\kern 1pt} Me_2 ]_n$$ (M = Ge, n = 1; M = Sn, n = 2): a theoretical study

Abstract

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 (ΔG 0 = −2.1 kcal mol−1) while that of 4b is thermally forbidden (ΔG 0 = 10.1 kcal mol−1), which is consistent with experimental data. The M←NMe2 coordination bond energies, ΔE 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.