Synthesis and characterization of hexaosmium carbonyl clusters containing pyridine ligands: crystal and molecular structures of [Os6(CO)15(µ4-η2-CO)(C5H5N)3], [Os6(CO)15(µ-H)(µ-CO)(µ3-O)(C5H5N)(µ-η2-NC5H4)] and [Os6(CO)14(µ-H)(µ-CO)(MeCN)(C5H5N)(µ-η2-NC5H4)]

Reaction of [Os6(CO)16(MeCN)2] with 1 equivalent of pyridine in CH2Cl2 at room temperature afforded three new clusters: [Os6(CO)15(µ4-η2-CO)(C5H5N)3] 1, [Os6(CO)15(µ-H)(µ-CO)(µ3-O)(C5H5N)(µ-η2-NC5H4)] 2 and [Os6(CO)14(µ-H)(µ-CO)(MeCN)(C5H5N)(µ-η2-NC5H4)] 3 in 32, 10 and 25% yields respectively. Both clusters 2 and 3 contain an orthometallated pyridine ligand but with different metal core geometries. The molecular structure of cluster 2 revealed the presence of a novel µ3-O group bridging three osmium centres