text: *Group 2 elements form [[Alkaline earth octacarbonyl complex|[M(CO)]]] (M = Ca, Sr, Ba), characterized in gas phase by mass spectrometry and vibrational spectroscopy.
  *Group 3 elements form [Sc(CO)] and [Y(CO)] in gas phase.
  *Group 7 elements as monocations resemble neutral group 6 derivative [M(CO)] (M = Mn, Tc, Re).
  *Group 8 elements as dications also resemble neutral group 6 derivatives [M(CO)] (M = Fe, Ru, Os).