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: Ru-8(-)-Ru-12(-) have simple cubic structures, Ru-13(-)-Ru-16(-) form double layered hexagonal structures, and larger clusters form close packed motifs. For Ru-17(-), we find hexagonal close packed stacking, whereas octahedral structures occur for Ru-18(-)-Ru-20(-). Our calculations also predict simple cubic structures for the smaller clusters Ru-4(-)-Ru-7(-), which were not accessible to electron diffraction measurements. (C) 2015 AIP Publishing LLC.