TbFCl 2 : Das erste Fluoridchlorid der dreiwertigen Lanthanoide

TbFCl 2 : The First Fluoride Chloride of the Trivalent Lanthanoids Single crystals of TbFCl 2 (monoclinic, C 2 /c ; a = 890.28(5), b = 581.56(3), c = 683.37(4) pm, β = 109.621(4)°; Z = 4) can be obtained by the reaction of TbCl 3 and TbF 3 under inert‐gas atmosphere in tantalum capsules (900 °C, 10 d) as colourless transparent lath‐shaped blocks. The crystal structure contains only one singular Tb 3+ cation which is eightfold coordinated by two F − (d(Tb 3+ −F − ) = 218 pm, 2×) and six Cl − anions (d(Tb 3+ −Cl − ) = 280−287 pm) forming a distorted square antiprism. The F − anions are linear surrounded by two Tb 3+ cations while the Cl − anions reside in a quasi ‐planar coordination of three Tb 3+ cations, therefore the Niggli formula for TbFCl 2 has to be $^{3}_{\infty}\rm \{TbF_{2/2}Cl_{6/3}\}$ . Terbium and fluorine form zigzag chains along the c axis that are not connected to each other and arrange like a hexagonal rod‐packing. These cationic chains $^{1}_{\infty}\rm \{[FTb_{2/2\prime}]^{2+}\}$ are mantled by Cl − anions which take care for the charge balance and the three‐dimensional cross‐linkage. The structural relationship of TbFCl 2 with YF 3 ‐type $\rm TbF_{3}( = ^{3}_{\infty}\rm \{Tb(F1)_{3/3}(F2)_{6/3}\})$ and PuBr 3 ‐type $\rm TbCl_{3}( = ^{2}_{\infty}\rm \{Tb(Cl1)_{2/2}(Cl2)_{6/3}\})$ will also be discussed.