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Functional small molecules afford opportunities to direct solid-state inorganic reactions at low temperatures. Here, we use catalytic amounts of organosilicon molecules to influence the metathesis reaction: FeCl 2 + Na 2 S 2 → 2NaCl + FeS 2 . Specifically, hexaphenyldisiloxane ((C 6 H 5 ) 6 Si 2 O) is shown to increase pyrite yields in metathesis reactions performed at 150 °C. In situ synchrotron X-ray diffraction (SXRD) paired with differential scanning calorimetry (DSC) reveals that diffusion-limited intermediates are circumvented in the presence of (C 6 H 5 ) 6 Si 2 O. Control reactions suggest that the observed change in the reaction pathway is imparted by the Si–O functional group. 1 H NMR supports catalytic behavior, as (C 6 H 5 ) 6 Si 2 O is unchanged ex post facto . Taken together, we hypothesize that the polar Si–O functional group coordinates to iron chloride species when NaCl and Na 2 S 4 form, forming an unidentified, transient intermediate. Further exploration of targeted small molecules in these metathesis reaction provides new strategies in controlling inorganic materials synthesis at low-temperatures. 

Many functional materials have relatively low decomposition temperatures ( T ≤ 400 °C), which makes their synthesis challenging using conventional high-temperature solid-state chemistry. Therefore, non-conventional techniques such as metathesis, hydrothermal, and solution chemistry are often employed to access low-temperature phases; the discovery of new chemistries is needed to expand access to these phases. This contribution discusses the use of triphenylphosphine (PPh 3 ) as a molten flux to synthesize superconducting iron selenide (Fe 1+δ Se) at low temperature ( T = 325 °C). Powder X-ray diffraction and magnetism measurements confirm the successful formation of superconducting iron selenide while nuclear magnetic resonance spectroscopy and in situ X-ray diffraction show that the formation of superconducting FeSe at low temperatures is enabled by an adduct between the triphenylphosphine and selenium. Exploration of the Fe–Se–PPh 3 phase space indicates that the PPh 3 –Se adduct effectively reduces the chemical potential of the selenium at high concentrations of triphenylphosphine. This contribution demonstrates that the use of a poorly-solvating yet reactive flux has the potential to enable the synthesis of new low-temperature phases of solid materials.