New coordination modes of an oxime ligand in a triosmium cluster. Stabilization by intra- and intermolecular C-H center dot center dot center dot O hydrogen bonds

Reaction of the hydroxyamine 7-chloro-4-(hydroxyamino)quinoline with the tr iosmium cluster Os-3-(CO)(10)(NCMe)(2) gave the complex (mu-H)Os-3(CO)(10)( mu(2)-eta(1)-O-C9H6N2Cl) (3), in which a new mode of mu(2)-eta(1)-O-oximato ligand bridged two osmium centers by an oxygen atom. This complex was slow ly converted to (mu-H)Os-3-(CO)(10)(mu(2)-eta(2)-ON-C9H6NCl) (4), where an aromatic C-H moiety in the mu(2)-eta(2)-ON-oximatoquinoline group formed an unusual short intramolecular C-H...O=N hydrogen bond and an intermolecular C-H...O=C hydrogen bond simultaneously. The formation of the intramolecula r hydrogen bond may provide a stabilization effect for the generation of th e eta(2)-ON complex 4 and a driving force fbr the transformation of 3 to 4.