Tuning the Competition between Hydrogen and Tetrel Bonds by a Magnesium Bond.

A computational study of the complexes formed by TF3 OH (T=C, Si, Ge) with three nitrogen-containing bases NCH, NH3 , and imidazole (IM) is carried out at the MP2/aug-cc-pVTZ level. TF3 OH can participate in two different types of noncovalent interactions: a hydrogen bond (HB) involving the hydroxyl proton and a tetrel bond (TB) with the tetel atom T. The strength of the HB is largely unaffected by the identity of T while the TB is enhanced as T grows larger. The HB is preferred over the TB for most systems, with the exception of GeF3 OH with either NH3 or IM. MgCl2 engages in a Mg⋅⋅⋅O Magnesium bond (Mg-bond) with the TF3 OH O atom, which cooperatively enhances both the HB and TB. The HB strengthening is particularly large for the NH3 or IM bases, and especially for CF3 OH, but is slowly reduced as the T atom grows larger. The TB enhancement, on the other hand, behaves in the opposite fashion, accelerating for the larger T atoms. As a bottom line, the Mg-bond generally reinforces and accentuates the preference for the HB or TB that is already present in the dimer. The Mg-bond is also responsible for a proton transfer in the HB configurations with NH3 and IM.