Ge Pairs and Sb Ribbons in Rare‐Earth Germanium Antimonides RE₁₂Ge_7−xSb₂₁ (RE=La–Pr)

Abstract

Abstract The ternary rare‐earth germanium antimonides RE 12 Ge 7− x Sb 21 ( RE =La–Pr; x =0.4–0.5) are synthesized by direct reactions of the elements. Single‐crystal X‐ray diffraction studies indicate that they adopt a new structure type (space group Immm , Z =2, a =4.3165(4)–4.2578(2) Å, b =15.2050(12)–14.9777(7) Å, c =34.443(3)–33.9376(16) Å in the progression from RE =La to Pr), integrating complex features found in RE 6 Ge 5− x Sb 11+ x and RE 12 Ga 4 Sb 23 . A three‐dimensional polyanionic framework, consisting of Ge pairs and Sb ribbons, outlines large channels occupied by columns of face‐sharing RE 6 trigonal prisms. These trigonal prisms are centered by additional Ge and Sb atoms to form GeSb 3 trigonal‐planar units. A bonding analysis attempted through a Zintl–Klemm approach suggests that full electron transfer from the RE atoms to the anionic substructure cannot be assumed. This is confirmed by band‐structure calculations, which also reveal the importance of GeSb and SbSb bonding. Magnetic measurements on Ce 12 Ge 6.5 Sb 21 indicate antiferromagnetic coupling but no long‐range ordering down to 2 K.