*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).