The occurrence of a heteroatom X (C, N, or O) in the MoFe7S9X core of the iron-molybdenum cofactor of nitrogenase has encouraged synthetic attempts to prepare high-nuclearity M-Fe-S-X clusters containing such atoms. We have previously shown that reaction of the edge-bridged double cubane [(Tp)(2)Mo2Fe6S8(PEt3)(4)] (1) with nucleophiles HQ-affords the clusters [(Tp)(2)Mo(2)Fe(6)S(8)Q(QH)(2)](3)- (Q = S, Se) in which HQ- is a terminal ligand and Q(2)- is a,mu(2)-bridging atom in the core. Reactions with OH- used as such or oxygen nucleophiles generated in acetonitrile from (Bu3Sn)(2)O or Me3SnOH and fluoride were examined. Reaction of 1 with Et4NOH in acetonitrile/water generates [(Tp)(2)Mo2Fe6S9(OH)(2)](3)- (3), isolated as [(Tp)(2)Mo2Fe6S9(OH)(OC(=NH)Me)(H2O)](3-) and shown to have the [MO2Fe6(mu(2)-S)(2)(mu(3)-S)(6)(mu(6)-S)] core topology very similar to the P-N cluster of nitrogenase. The reaction system 1/Et4NOH in acetonitrile/methanol yields the P-N-type cluster [(TP)(2)MO2Fe6S9(OMe)(2)(H2O)](3-) (5). The system 1/Me3SnOH/Faffords theoxo-bridged double P-N -type cluster {[(Tp)(2)Mo2Fe6S9(mu(2)-O)](2)}(5-) (7), convertible to the oxidized cluster {[(Tp)(2)Mo2Fe6S9(mu(2)-O)](2)}(4-) (6), which is prepared independently from [(Tp)(2)Mo2Fe6S9F2(H2O)](3-)/(Bu3Sn)(2)O. In the preparations of 3-5 and 7, hydroxide liberates sulfide from 1 leading to the formation of P-N-type clusters. Unlike reactions with HQ-, no oxygen atoms are integrated into the core structures of the products. However, the halfdimer composition [Mo2Fe6S9O] relates to the MoFe7S9 consitution of the putative native cluster with X = O. (Tp = hydrotris(pyrazolyl) borate(1-)).