Density functional theory (DFT) is used to obtain the first structural characterization of the unsaturated dichromium carbonyl Cr-2(CO)(9), which is predicted to have a remarkably short metal-metal bond length of 2.31 Angstrom (B3LYP) or 2.28 Angstrom (BP86). This chromium-chromium distance is essentially identical to that reported experimentally for the established Cr=Cr triple bond in (eta(5)-Me5C5)(2)Cr-2(CO)(4). The dissociation energy to the fragments Cr(CO)(4) and Cr(CO)(5) is determined to be 32 kcal/mol (B3LYP) or 43 kcal/mol (BP86). For comparison, the Cr-2(CO)(10) molecule and the saturated Cr-2(CO)(11) system have negligible dissociation energies. The minimum energy Cr-2(CO)(9) structure is of C-s symmetry with the two chromium atoms asymmetrically bonded to the bridging carbonyls. However, within 0.1 kcal/mol lies a C-2 symmetry structure with one symmetric and two asymmetric bridging carbonyls. Furthermore, the high symmetry D-3h structure analogous to Fe-2(CO)(9) lies only similar to1 kcal/mol higher in energy The Cr-2(CO)(9) molecule is thus highly fluxional. The extremely flat potential energy surface in the region adjacent to these minima suggests that Cr-2(CO)(9) will be labile. The relationship between the Cr-2(CO)(9) molecule and the experimentally known binuclear manganese (eta(5)-Me5C5)(2)Mn-2(mu-CO)(3) compound is explored.