Compounds with Two Metal−Metal Multiple Bonds:  New Ways of Making Doublets into Cyclic Quartets

New types of products obtained by combining two dinuclear multiply metal−metal bonded species (doublets) to obtain cyclic tetranuclear products (quartets) are reported. One new type consists of pairs of quadruply bonded Mo₂⁴⁺ units united by two μ-X links (X = H, OH, O) although in the last case oxidation has also occurred so that these are Mo₂⁵⁺ moieties. In these cases, the subunits are Mo₂(DArF)₃. The second new type consists of Mo₂(DArF)₂ subunits linked by four μ-X bridges, where X = Cl, Br, I. The previously known compound Mo₄I₈(PBuⁿ₃)₄ has been shown to differ from all previously known Mo₄X₈(PR₃)₄ molecules (X = Cl, Br) by retaining two quadruple bonds instead of being a metallacyclobutadiyne, as are the others.