Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO 2 .

The reactivity of alkali-manganese(II) and alkali trifluoroacetates towards amorphous SiO 2 (a-SiO 2 ) was studied in the solid-state. K 4 Mn 2 (tfa) 8 , Cs 3 Mn 2 (tfa) 7 (tfaH), KH(tfa) 2 , and CsH(tfa) 2 (tfa = CF 3 COO - ) were thermally decomposed under vacuum in fused quartz tubes. Three new bimetallic fluorotrifluoroacetates of formulas K 4 Mn 3 (tfa) 9 F, Cs 4 Mn 3 (tfa) 9 F, and K 2 Mn(tfa) 3 F were discovered upon thermolysis at 175 °C. K 4 Mn 3 (tfa) 9 F and Cs 4 Mn 3 (tfa) 9 F feature a triangular-bridged metal cluster of formula [Mn 3 (μ 3 -F)(μ 2 -tfa) 6 (tfa) 3 ] 4- . In the case of K 2 Mn(tfa) 3 F, fluoride serves as an inverse coordination center for the tetrahedral metal cluster K 2 Mn 2 (μ 4 -F). Fluorotrifluoroacetates may be regarded as intermediates in the transformation of bimetallic trifluoroacetates to fluoroperovskites KMnF 3 , CsMnF 3 , and Cs 2 MnF 4 , which crystallized between 250 and 600 °C. Decomposition of these trifluoroacetates also yielded alkali hexafluorosilicates K 2 SiF 6 and Cs 2 SiF 6 as a result of the fluorination of fused quartz. The ability to fluorinate fused quartz was observed for monometallic alkali trifluoroacetates as well. Hexafluorosilicates and heptafluorosilicates K 3 SiF 7 and Cs 3 SiF 7 were obtained upon thermolysis of KH(tfa) 2 and CsH(tfa) 2 between 200 and 400 °C. This ability was exploited to synthesize fluorosilicates under air by simply reacting alkali trifluoroacetates with a-SiO 2 powder.