Synthesis, crystal growth and structure of KEu2[Si4O10]F

K 2 Eu 4 {1 B, 1∞ 2 }[ 6 Si 8 O 20 ]F 2 , prepared by flux-melting of Eu 2 O 3 , SiO 2 and Si in KF under reducing conditions crystallizes with the monoclinic cell, P2 1 /n, a = 1149.9(3) pm, b = 848.8(2) pm, c = 1162.6(4) pm, β = 112.10(1)°, Z = 4. The structure determination led to R = 7.3% (R w = 3.7%). The new silicate-fluoride contains strongly folded silicate sheets of connected four-membered rings, separated by interlayers of europium(II) and fluoride. The potassium ions are located in the «half-pipes» that are formed by the silicate sheet. The structure of the silicate anion is related to that of apophyllite, KCa 4 {uB, 1∞ 2 }[ 4 Si 4 O 10 ] 2 (F, OH).8H 2 O