Molecular Structures of the Pyridine-2-olates Ph<i>E</i>(pyO)₃ (<i>E</i> = Si, Ge, Sn)—[4+3]-Coordination at Si, Ge vs. Heptacoordination at Sn

Abstract

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···N separations ca. 3.0 Å), 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···N separations (2.8–2.9 Å) indicate a trend toward tetrel hypercoordination. PhSn(pyO)3 features heptacoordinate tin within a pentagonal bipyramidal Sn coordination sphere (Sn···N separations 2.2–2.4 Å). For the Si and Sn compounds, 29Si and 119Sn NMR spectroscopy indicates retention of their tetrel coordination number in chloroform solution.

Keywords

• 2-hydroxypyridine
• hypercoordination
• ¹¹⁹Sn solid-state NMR
• tetrel
• X-ray diffraction