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1.  Monohalogenated ferrocenes C5H5FeC5H4 X (X = Cl, Br and I) and a second polymorph of C5H5FeC5H4I 
The structures of the three title monosubstituted ferrocenes, namely 1-chloro­ferrocene, [Fe(C5H5)(C5H4Cl)], (I), 1-bromo­ferrocene, [Fe(C5H5)(C5H4Br)], (II), and 1-iodo­ferrocene, [Fe(C5H5)(C5H4I)], (III), were determined at 100 K. The chloro- and bromo­ferrocenes are isomorphous crystals. The new triclinic polymorph [space group P , Z = 4, T = 100 K, V = 943.8 (4) Å3] of iodo­ferrocene, (III), and the previously reported monoclinic polymorph of (III) [Laus, Wurst & Schottenberger (2005 ▶). Z. Kristallogr. New Cryst. Struct. 220, 229–230; space group Pc, Z = 4, T = 100 K, V = 924.9 Å3] were obtained by crystallization from ethanolic solutions at 253 and 303 K, respectively. All four phases contain two independent mol­ecules in the unit cell. The relative orientations of the cyclo­penta­dienyl (Cp) rings are eclipsed and staggered in the independent mol­ecules of (I) and (II), while (III) demonstrates only an eclipsed conformation. The triclinic and monoclinic polymorphs of (III) contain nonbonded inter­molecular I⋯I contacts, causing different packing modes. In the triclinic form of (III), the mol­ecules are arranged in zigzag tetra­mers, while in the monoclinic form the mol­ecules are arranged in zigzag chains along the a axis. Crystallographic data for (III), along with the computed lattice energies of the two polymorphs, suggest that the monoclinic form is more stable.
doi:10.1107/S0108270109034763
PMCID: PMC2773730  PMID: 19893225
2.  Insight into the structures of [M(C5H4I)(CO)3] and [M 2(C12H8)(CO)6] (M = Mn and Re) containing strong I⋯O and π(CO)–π(CO) inter­actions 
The compounds tricarbonyl(η5-1-iodo­cyclo­penta­dienyl)­man­gan­ese(I), [Mn(C5H4I)(CO)3], (I), and tricarbonyl(η5-1-iodo­cyclo­penta­dienyl)rhenium(I), [Re(C5H4I)(CO)3], (III), are isostructural and isomorphous. The compounds [μ-1,2(η5)-acetyl­enedicyclo­penta­dienyl]bis­[tricarbonyl­manganese(I)] or bis­(cymantrenyl)acetyl­ene, [Mn2(C12H8)(CO)6], (II), and [μ-1,2(η5)-acetyl­enedicyclo­penta­dienyl]bis­[tri­carbonyl­rhenium(I)], [Re2(C12H8)(CO)6], (IV), are isostructural and isomorphous, and their mol­ecules display inversion symmetry about the mid-point of the ligand C C bond, with the (CO)3 M(C5H4) (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 π(CO)–π(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 π(Csp 2)–π(Csp 2) stacking inter­actions between pairs of mol­ecules. The π(CO)–π(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.
doi:10.1107/S0108270109035902
PMCID: PMC2773731  PMID: 19893226

Results 1-2 (2)