Trivalent group 14 radicals

Such compounds can be categorized into three different types, depending on the structure (or equivalently the orbital in which the unpaired electron resides) and the energetic barrier to inversion.

And a planar structure with an electron that typically would reside in a pure p orbital is denoted as Type C. The structure of such molecules has been determined by probing the nature of the orbital that the unpaired electron resides in using spectroscopy, as well as directly with X-ray methods.

The most recent large advance has been the characterization of the first stable trivalent lead radical, as described in 2007.

Firstly electronic stabilization, the tetrel is connected to an electron-rich atom such as oxygen, nitrogen, or fluorine.

This class of molecules tends to be slightly more stable than the acyclic analogues as there is a stabilization through the delocalization of the unpaired electrons within the π-system.

The isotropic component of the hyperfine coupling to the central tetrel scales proportionally with the spin density in the valence s orbital on that atom (see the Figure on the right).

[13] There is also a correlation between the g-shift (∆g = gmeas - ge) and the geometry for series of compounds with ligands of similar electronegativities.

[11][20] It has also been demonstrated using tris(trialkylsilyl)silyl radicals that the more bulky the ligands are, the more a planar structure will be favored, and the lower the hyperfine coupling constant will be.

The natural bond orbitals (NBO) corresponding to the unpaired electron in various simple trivalent tetrel radicals (R 3 E• for E = C, Si, Ge and R = H, F, Me). Each NBO is decomposed into the percent composition of valence s and p orbital contributions. R 3 C• and R 3 Si• calculated at B3LYP/6-311G**++ and R 3 Ge• calculated at B3LYP/cc-pVDZ++ using Jaguar (NBO 6.0). [ 1 ] These values differ slightly from that calculated using the shell analysis based on pseudo-orbital theory, however the trends remain. [ 2 ] Changes in composition of these orbitals is well described by Bent's rule .
The correlation of the spin density in the valence s orbital (calculated by the ratio of the isotropic hyperfine coupling constant to the theoretical hyperfine splitting in a pure s orbital) against the g-shift (normalized by the spin-orbit coupling constant). (Black) Si, (Blue) Ge, (Red) Sn, and (Green) Pb. (Circles [ 13 ] ), (Triangles [ 14 ] ), (Square [ 9 ] ). Spin-orbit coupling constants from [ 15 ] [ 16 ] [ 17 ] [ 18 ]