The crystal and molecular structure of tricarbonyltetrakis(trifluoromethyl)cyclopentadienone-iron

Intermolecular Carbonyl···Carbonyl Interactions in Transition-Metal Complexes

We performed a comprehensive analysis of intermolecular carbonyl-carbonyl interactions in transition-metal complexes. Those interactions can be classified in two main types depending on the organometallic or organic nature of the donor carbonyl: M-CO···CO and R-CO···CO, respectively. By means of a combined structural and computational study we unraveled their geometrical features and strength. Moreover, electronic structure, natural bond orbitals, energy decomposition analysis, and quantum theory of atoms in molecules calculations were performed to try to understand their nature. Remarkably, we discovered that these carbonyl-carbonyl contacts have several features of the n → π* interaction. The charge transfer from an oxygen lone pair to an empty antibonding π orbital of the acceptor carbonyl is also accompanied by an electrostatic O^δ-···C^δ+ interaction. To the best of our knowledge this is the first report of an intermolecular n → π* interaction in metal complexes. These results might be significant, for instance, for the catalytic activation of carbonyl-containing small molecules with metal compounds or in the design of hybrid organic-inorganic materials, metal-organic frameworks, and other extended structures.

The crystallography and electron distribution of octafluorocyclohexa-1, 3-dieneiron tricarbonyl

Octafluorocyclohexa-1, 3-dieneiron tricarbonyl crystallizes in the orthorhombic system with a = 13.49 Å, b = 6.92 Å, c = 11.89 Å, Z = 4, M = 364, space group Pcam . The molecule has exact m(C s ) symmetry in the crystal, the metal-carbon bond lengths being reported with e. s. d. of 0.007 to 0.013 Å, the average standard deviations of the carbon–carbon, carbon–fluorine and carbon–oxygen bonds being 0.013 Å. The conformation of the cyclohexadiene ligand suggests the value of a σ – π description of the metal-ligand bonding although a molecular orbital scheme allows a more quantitative discussion of the molecular geometry. The carbonyl groups are distorted from exact C 3 v symmetry, their precise arrangement, correlated with the stereochemistry of other molecules, allowing a re-examination of the probable bonding in butadieneiron tricarbonyl. The atomic thermal motions and crystal structure are also discussed.