Bonding analysis in ytterbium(ii) distannyl and related tetryls

Abstract

The syntheses of the ytterbium(II) distannyl [Yb{Sn(SiMe₃)₃}₂·(thf)₄] (Yb–Sn) and of its digermyl analogue [Yb{Ge(SiMe₃)₃}₂·(thf)₃] (Yb–Ge) are presented. The compounds were characterised by multinuclear high-resolution solution NMR spectroscopy, including ¹⁷¹Yb NMR, and by X-ray diffraction crystallography. The bonding and electronic properties of the two complexes, along with those of the known ytterbium(II) disilyl derivative [Yb{Si(SiMe₃)₃}₂·(thf)₃] (Yb–Si) and those of the congeneric calcium distannyl [Ca{Sn(SiMe₃)₃}₂·(thf)₄] (Ca–Sn), were investigated in detail by DFT calculations. This analysis points at a primarily ionic Yb-tetrel bonding, with a small covalent contribution, attributed principally to the 5d(Yb) participation. This weak covalent character is found to be larger for the distannyl Yb–Sn than for its lighter Si- and Ge-derivatives. The covalent component is also found to be greater in Yb–Sn than in Ca–Sn, due to the availability of the 5d(Yb) orbitals for bonding.