The existence of ions [Pn 3 ] 3-for Pn (Pnictide) ) As, Sb, or Bi in liquid ammonia was proposed initially by Zintl seventy years ago. 1 Later, some of these Zintl ions were observed in molten salts, but had not been isolated and structurally characterized before. 2 Our interest in such species started with the discovery of the naked double-bonded molecule [BidBi] 2-in (K-crypt) 2 -Bi 2 (crypt ) 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane) crystallized from an ethylenediamine solution of the compound K 3 Bi 2 . 3 The latter, itself, contains the [Bi 2 ] 2-dimer but has also an extra electron that is delocalized over the structure to make the compound metallic. 4 A second precursor compound, K 5 Bi 4 with zigzag tetramers of [Bi 4 ] 4-and also with a delocalized "extra" electron, was found in this system as well. 5 It also readily dissolves in ethylenediamine and crypt, and the same compound (K-crypt) 2 Bi 2 containing the bismuth dimers [Bi 2 ] 2-can be crystallized from the solution. More oxidized species, squares of [Bi 4 ] 2-in (K-crypt) 2 Bi 4 , are also known. 6 These observations imply possible coexistence of a variety of bismuth species in these solutions. We have not been able to crystallize any other "naked" species yet, but we have been successful in stabilizing the trimer [Bi 3 ] 3-by coordinating it to two transition-metal (M) tricarbonyl species, Cr(CO) 3 and Mo(CO) 3 . We report here the synthesis and structure of the heteroatomic clusters [Bi 3 Cr 2 (CO) 6 ] 3-and [Bi 3 Mo 2 (CO) 6 ] 3-with the shape of trigonal bipyramids made of bent [Bi 3 ] 3-and two equatorial M(CO) 3 groups.Transition-metal tricarbonyl fragments of M(CO) 3 have been used before in combinations with existing Zintl anions such as [E 9 ] 4-in [K-crypt] 4 [E 9 Cr(CO) 3 ] for E ) Sn and Pb 7 and [Pn 7 ] 3-in [K-crypt] 3 [Pn 7 M(CO) 3 ] for Pn ) P, As, and Sb and M ) Cr, Mo, and W, 8 and have proven very effective in forming such heteroatomic species. At the same time, it is surprising that despite the extensive studies of Zintl ions made of the lighter pnictides P, As, and Sb, 9 there is very little done with the heaviest homologue bismuth. On the other hand, a number of bismuthtransition metal compounds made by a different approach, i.e., without the use of Zintl ions, have been reported recently. 10 The new compounds K(K-crypt) 5 [Bi 3 M 2 (CO) 6 ] 2 ‚3en, where M ) Cr (1) or Mo (2) and en ) ethylenediamine, were synthesized by reacting ethylenediamine solutions of K 5 Bi 4 and crypt either with solid (mesitylene)Cr(CO) 3 or (cycloheptatriene)Mo(CO) 3 , respectively, or with their toluene solutions. The color changes quickly from blue-green for the ethylenediamine solution of the precursor (absorption at 434 and 604 nm) to brown-red for the product (absorption at 360 and 500 nm measured for 2). Crystals of 1 and 2, both with the same brown-red color, crystallize in a week (about 40% yield for both 1 and 2, based on the amount of dissolved precursor) as a result of the slow diffusion of carefully layered tolue...