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) [Os₃(μ-H)(CO)₁₀(μ-NC₅H₃ C₅H₃N)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-NC₅H₃C ₅H₄N)}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 't_2g' set orbitals of the W(CO)₅ fragment as the HOMO orbitals.