18-electron complexes questioned

Abstract

Last year chemists reported that bonding long considered exclusive to transition metals could occur with barium, calcium, and strontium. Mingfei Zhou of Fudan University, Gernot Frenking of Nanjing Tech University and the Philipp University of Marburg, and colleagues reported that these atoms formed 18-electron complexes with 8 carbon monoxide molecules at 4 K (Science 2018, DOI: 10.1126/science.aau0839). But the unexpected results generated skepticism among other chemists. Clark R. Landis of the University of Wisconsin–Madison and colleagues argue that, though they don’t doubt that octocarbonyl complexes were made, the group’s bonding analysis ignored the known chemistry of metals and CO (Science 2019, DOI: 10.1126/science.aay2355). Zhou and Frenking’s bonding analysis assumes that the metal and octocarbonyl are neutral fragments. Landis’s team redid the analysis assuming those fragments were charged, which Landis says better reflects the complexes’ electron density distribution. They did not observe the...