Structural evolution of small ruthenium cluster anions

The structures of ruthenium cluster anions have been investigated using a combination of trapped ion electron diffraction and density functional theory computations in the size range from eight to twenty atoms. In this size range, three different structural motifs are found: Ru8−–Ru12− have simple cubic structures, Ru13−–Ru16− form double layered hexagonal structures, and larger clusters form close packed motifs. For Ru17−, we find hexagonal close packed stacking, whereas octahedral structures occur for Ru18−–Ru20−. Our calculations also predict simple cubic structures for the smaller clusters Ru4−–Ru7−, which were not accessible to electron diffraction measurements.