Insight into the structures of [M(C(5)H(4)I)(CO)(3)] and [M(2)(C(12)H(8))(CO)(6)] (M = Mn and Re) containing strong I...O and pi(CO)-pi(CO) interactions.

The compounds tricarbonyl(eta(5)-1-iodocyclopentadienyl)manganese(I), [Mn(C(5)H(4)I)(CO)(3)], (I), and tricarbonyl(eta(5)-1-iodocyclopentadienyl)rhenium(I), [Re(C(5)H(4)I)(CO)(3)], (III), are isostructural and isomorphous. The compounds [mu-1,2(eta(5))-acetylenedicyclopentadienyl]bis[tricarbonylmanganese(I)] or bis(cymantrenyl)acetylene, [Mn(2)(C(12)H(8))(CO)(6)], (II), and [mu-1,2(eta(5))-acetylenedicyclopentadienyl]bis[tricarbonylrhenium(I)], [Re(2)(C(12)H(8))(CO)(6)], (IV), are isostructural and isomorphous, and their molecules display inversion symmetry about the mid-point of the ligand C[triple-bond]C bond, with the (CO)(3)M(C(5)H(4)) (M = Mn and Re) moieties adopting a transoid conformation. The molecules in all four compounds form zigzag chains due to the formation of strong attractive I...O [in (I) and (III)] or pi(CO)-pi(CO) [in (I) and (IV)] interactions along the crystallographic b axis. The zigzag chains are bound to each other by weak intermolecular C-H...O hydrogen bonds for (I) and (III), while for (II) and (IV) the chains are bound to each other by a combination of weak C-H...O hydrogen bonds and pi(Csp(2))-pi(Csp(2)) stacking interactions between pairs of molecules. The pi(CO)-pi(CO) contacts in (II) and (IV) between carbonyl groups of neighboring molecules, forming pairwise interactions in a sheared antiparallel dimer motif, are encountered in only 35% of all carbonyl interactions for transition metal-carbonyl compounds.