Fe2 pairs as structural units in the indides RE12Fe2In3 (RE = Ho, Er, Tm, Lu)

The indides RE12Fe2In3 (RE = Ho, Er, Tm, Lu) have been prepared by arc-melting the elements and subsequent annealing. All compounds were characterized by X-ray powder diffraction and the Er12Fe2In3 structure was refined from X-ray single crystal data: I4/mmm, alpha = 958.8(1), c = 957.8(1) pm, wR2 = 0.0629, 412 F-2 values and 22 variables. The 2 alpha site shows In/Fe mixing, leading to the composition Er12Fe2.31In2.69 for the investigated crystal. The structure (new type) derives from a Cu3Au ( RE12In4) like arrangement RE12(T-2)In-3, where one fourth of the indium sites is substituted by an Fe-2 dumb-bell at an Fe-Fe distance of 224 pm. The Er12Fe2In3 type is discussed in line with the structures of Er6Co2.19In0.81 ( RE12(T-2)(2)In-2) and Sm12Ni6In( RE12(T-2)(3)In), where two, respectively three indium sites are substituted by transition metal dumb-bells.