Synthesis, characterization and theoretical studies of new heterometallic carbonyl clusters bridged by 4,4′-dipyridyl unit

4,4′-Bipyridine (4,4′-bipy) reacts with the activated cluster [Os3(CO)10(NCMe)2] readily at room temperature to give a mixture of [Os3(μ-H)(CO)10(μ-NC5H3C5H4N)] (1) and [Os3(μ-H)(CO)10(μ-NC5H3C5H3N)Os3(μ-H)(CO)10] (2), the composition of which depends upon the reaction conditions and the ratio of the reactants. The reactivities of the metalloligand precursor 1 with a pendant nitrogen atom towards [W(CO)5(THF)] and [Re(CO)5Cl] have been investigated, affording two new heterometallic clusters [Os3(μ-H)(CO)10(μ-NC5H3C5H4N)W(CO)5] (3) and [ReCl(CO)3{Os3(μ-H)(CO)10(μ-NC5H3C5H4N)}2] (4) in moderate to good yields. Compound 4 can also be prepared from the reaction between [Os3(CO)10(NCMe)2] and [ReCl(CO)3(4,4′-bipy)2]. The X-ray crystal structures of compounds 1–3 have been determined and molecular orbital calculations on these complexes using density functional theory (DFT) method reveal that they all have similar orbitals in the LUMO region. Clusters 1 and 2 have the OsOs σ-bonding orbitals as their HOMO orbitals while cluster 3 has the ‘t2g’ set orbitals of the W(CO)5 fragment as the HOMO orbitals.