Search for: All records

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. 

A new synthetic route to access pristine and rare-earth-doped BaFBr nanocrystals is described. Central to this route is an organic–inorganic hybrid precursor of formula Ba 5 (CF 2 BrCOO) 10 (H 2 O) 7 that serves as a dual-halogen source. Thermolysis of this precursor in a mixture of high-boiling point organic solvents yields spherical BaFBr nanocrystals (≈20 nm in diameter). Yb:Er:BaFBr nanocuboids (≈26 nm in length) are obtained following the same route. Rare-earth-doped nanocrystals display NIR-to-visible photon upconversion under 980 nm excitation. The temperature-dependence of the green emission from Er 3+ may be exploited for optical temperature sensing between 150 and 450 K, achieving a sensitivity of 1.1 × 10 −2 K −1 and a mean calculated temperature of 300.9 ± 1.5 K at 300 K. The synthetic route presented herein not only enables access to unexplored upconverting materials but also, and more importantly, creates the opportunity to develop solution-processable photostimulable phosphors based on BaFBr.