The dianion [ Felr,( C0),,l2-can be obtained b y reduction of an equimolar mixture of [ Fe( CO),] and [Ir,(CO),,] in alcoholic NaOH and under 1 atm of carbon monoxide. The salt [N( PPh,),], [Felr,( CO),,] (1) crystallizes in the triclinic space group P i with unit-cell dimensions The mean values of the Fe-lr and Ir-lr distances are 2.648 and 2.708 A, respectively. In the derivative (1) the trigonal bipyramid is considerably elongated in the direction of the apical atoms, when compared with that in (2). This elongation is consistent with the increased number of cluster valence electrons: 76 in (1 ) and 7 2 in (2).Transition-metal clusters are attracting a great deal of interest with respect to their potential as catalysts. Particularly mixedmetal clusters are extensively studied because adjacent metal centres formed by different elements offer the possibility for co-operative reactions leading to new, more active, or more selective catalysts.' -3 Moreover, they should act as potential precursors of bimetallic heterogeneous catalysts of well defined st~icheiometry.~ The lack of an extensive work on Fe-Ir bimetallic clusters5 and recent reports on Fe-lr traditional catalysts, very selective for the production of MeOH from C O and H2,6--8 prompted us to investigate this field. In this paper we describe the synthesis, the chemical characterization, and the solid-state structures of the two new clusters [N(PPh,),], [Felr,(CO),,] (1) and(2), the first examples of Fe-lr mixedmetal carbonyl clusters. Results and DiscussionPi-epurutioi? I?f' [FeIr,(CO), 5]2 -(l).