The CN ligands in the isotypic compounds Sr3
] und Ba3
] have lost their "innocence" by higher reduction and weakening of the C–N bond, for the first time. For cobalt a closed-shell (d10
)-configuration was determined. The resulting mesomeric structures of the trigonal-planar complex anions, [Co1–
open new insight into the chemistry of metalates and coordination compounds of transition metals with CN ligands. Finally, consequences on the chemistry of carbonylmetalates can be expected, too.