Die Kettenstrukturen der ternären Eisen(III)fluoride Rb₂FeF₅ und (CH₃NH₃)₂FeF₅ / The Chain Structures of the Ternary Iron(III) Fluorides Rb₂FeF₅ and (CH₃NH₃)₂FeF₅

Abstract

Single crystals of the orthorhombic compounds Rb,FeF 5 (a = 756.5(1), b = 581.0(1), c = 1200.2(1) pm) and (CH 3 NH 3 ) 2 FeF 5 (a = 935.7(1), b = 789.6(1), c = 1017.2(1) pm) have been prepared and their structures determined by X-ray methods (wR = 0.025 and 0.029 for 983 and 954 reflections, resp.). Both compounds crystallize with Z = 4 in space group Pnma, but they form different chain structures: Rb 2 FeF 5 , isostructural with Rb,CrF 5 , exhibits cis-connected octahedra (bridging vs. average terminal Fe–F = 204.4/189.2 pm; Fe–F–Fe = 180°). In (CH 3 NH 3 ) 2 FeF 5 , related to the (NH 4 ),MnF 5 structure type, the octahedra are trans-connected (Fe–F = 199.4/190.7 pm; Fe–F–Fe = 164.0°). These differences and the influence of hydrogen bonds (average N–H···F = 278.9 pm) in the methylammonium compound are discussed along with relations to further fluoride structures.