An experimental evidence of a metal-metal bond in μ-carbonylhexacarbonyl[μ-(5-oxofuran-2(5H)-ylidene-κC,κC)]- dicobalt(Co-Co)[Co2(CO)6(μ-CO)(μ-C4O2H2)]

The orthorhombic crystal structure of [Co-2(CO)(3)(mu -CO)(mu -C4O2H2)] (1) was determined at 150 K(Fig. 1). Two C - H . . . O bonds connect the molecules. forming waving ribbons along the b axis. The experimental electron density. determined with the aspherical-atom formalism. was analyzed with the topological theory of molecular structure. The presence of the Co - Co bond critical point indicates for the first time the existence of a metal-metal bond in a system with bridged ligands. The bond critical properties of the intramolecular bonds and of the intermolecular interactions show features similar to those found in [Mn-2(CO)(10)], confirming our previously established bonding classification for organometallic and coordination compounds.