The reactions between K 5 Bi 4 , [(C 6 H 6 )Cr(CO) 3 ] or [(C 7 H 8 )Mo(CO) 3 ], and [2.2.2]crypt in liquid ammonia yielded the compounds [K([2.2.2]crypt)] 3 (η 3 -Bi 3 )M(CO) 3 ·10NH 3 (M = Cr, Mo), which crystallize isostructurally in P2 1 /n. Both contain an 18 valence electron piano-stool complex with a η 3 -coordinated Bi 3 -ring ligand.