Structural rearrangements induced by acid-base reactions in metal carbonyl clusters: the case of [H(3-n)Co15Pd9C3(CO)38]n- (n = 0-3).

The new bimetallic [HCo15Pd9C3(CO)(38)](2-) tri-carbide carbonyl cluster has been obtained from the reaction of [H2Co20Pd16C4(CO)(48)](4-) with an excess of acid in CH2Cl2 solution. The mono-hydride di-anion can be reversibly protonated and deprotonated by means of acid-base reactions leading to closely related [H3-nCo15Pd9C3(CO)(38)](n-) (n = 0-3) clusters. The crystal structures of the three anionic and the neutral clusters have been determined as their H3Co15Pd9C3(CO)(38)center dot 2thf, [NEt4][H2Co15Pd9C3(CO)(38)]center dot 0.5C(6)H(14), [NMe3(CH2Ph)](2)[HCo15Pd9C3(CO)(38)]center dot C6H14 and [NEt4](3)[Co15Pd9C3(CO)(38)]center dot thf salts. They are composed of a Pd-9(mu(3)-CO)(2) core stabilised by three Co5C(CO)(12) organometallic fragments. The poly-hydride nature of these clusters has been indirectly inferred via chemical, electrochemical and magnetic measurements. Besides, cyclic voltammetry shows that the [H3-nCo15Pd9C3(CO)(38)](n-) (n = 1-3) anions are multivalent, since they undergo two or three reversible oxidations. SQUID measurements of [HCo15Pd9C3(CO)(38)](2-) indicate that this even electron cluster is paramagnetic with two unpaired electrons, giving further support to its hydride nature. Finally, structural studies show that the Pd-9 core of [H3-nCo15Pd9C3(CO)(38)](n-) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H3-nCo15Pd9C3(CO)(38)](n-) (n = 2,3) anions. Such a significant structural rearrangement of the metal core of a large carbonyl cluster upon protonation-deprotonation reactions is unprecedented in cluster chemistry, and suggests that interstitial hydrides may have relevant stereochemical effects even in large carbonyl clusters.