Eu₃Co₂In₁₅ and KM₂In₉ (M = Co, Ni): 3D Frameworks Based on Transition Metal Centered In₉ Clusters

The title three compounds have been synthesized by solid state reactions at high temperatures, with excess indium as flux, and structurally characterized by single-crystal X-ray diffraction studies. Eu3Co2In15 forms a new structure type and crystallizes in the tetragonal space group P4/mbm (No. 127), whereas KM2In9 (M = Co, Ni) in the BaFe2Al9 type crystallizes in the hexagonal space group P6/mmm (No. 191). Their structures all feature a three-dimensional anionic framework based on 1D [MIn6] single cluster chains composed of face-sharing [MIn9] clusters. In Eu3Co2In15, two adjacent [CoIn6] single cluster chains form a [Co2In11] double cluster chain via corner-sharing In atoms as well as In−In bonds; the latter chains are further interconnected by additional indium atoms via In−In bonds into a complicated 3D framework, forming two types of tunnels along the c-axis, which are filled by the europium atoms. In KM2In9, the [MIn6] single cluster chains are directly interconnected via corner sharing and exo In−In bonds into a 3D framework with the K+ ions encapsulated in the 1D tunnels along the c-axis. Band structure calculations of three compounds based on density functional theory methods indicate that all three compounds are metallic.