Knowledge Bank

The asymmetric stretching frequency of $MgF2$ was monitored as a function of the number of complexing molecules. The molecular complexes $MgF2$ (M) x where X varies from one to four for $O2$, $N2$ and CO, one to three for $H2s$ and one for $SO2$ have been observed. It was generally found that the addition of a complexing molecule caused a decrease in the $MgF2$ asymmetric frequency. The decrease was observed to be approximately the same for the addition of each successive molecule. For the $N2$ complex four dinitrogen molecules cause the frequency to decrease to a value close to that of a pure $N2$ matrix. Thus, there are only four important interaction sites around the $MgF2$ molecule. The binding energy per molecule was estimated by taking the percent decrease in the force constant of $MgF2$ as a measure of the weakening of the $MgF2$ bond and assuming the loss in energy to be the minimum total binding energy for the complexing species. The bond strengths per molecule in kcal are as follows relative to $Ar:Ne(+3.7),Ar(0),02(-2,9)N2(-8.3),CO(-12.7),H2S(-22.7)$ and $SO2(-41.6)$. A new band near $547cm-1$ appeared in all experiments where a complex, was formed and is thought to be the symmetric stretching mode of $MgF2$ in the complex.