Molecular Structures of the Pyridine-2-olates PhE(pyO)(3) (E = Si, Ge, Sn)-[4+3]-Coordination at Si, Ge vs. Heptacoordination at Sn

The phenyltetrel pyridine-2-olates PhE(pyO)(3) (E = Si, Ge, Sn; pyO = pyridine-2-olate) were synthesized from the respective chlorides PhECl3 and 2-hydroxypyridine (2-pyridone) with the aid of a sacrificial base (triethylamine). Their solid-state structures were determined by single-crystal X-ray diffraction. PhSi(pyO)(3) exhibits a three-fold capped tetrahedral Si coordination sphere ([4+3]-coordination, Si center dot center dot center dot N separations ca. 3.0 angstrom), in accordance with structures of previously reported silicon pyridine-2-olates. PhGe(pyO)(3) adopts a related [4+3]-coordination mode, which differs in terms of the tetrahedral faces capped by the pyridine N atoms. Additionally, shorter Ge center dot center dot center dot N separations (2.8-2.9 angstrom) indicate a trend toward tetrel hypercoordination. PhSn(pyO)(3) features heptacoordinate tin within a pentagonal bipyramidal Sn coordination sphere (Sn center dot center dot center dot N separations 2.2-2.4 angstrom). For the Si and Sn compounds, Si-29 and Sn-119 NMR spectroscopy indicates retention of their tetrel coordination number in chloroform solution.