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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.  From small structural modifications to adjustment of structurally dependent properties: 1-methyl-3,5-bis­[(E)-2-thienyl­idene]-4-piperidone and 3,5-bis­[(E)-5-bromo-2-thienyl­idene]-1-methyl-4-piperidone 
The mol­ecules of the title compounds, C16H15NOS2, (I), and C16H13Br2NOS2, (II), are E,E-isomers and consist of an extensive conjugated system, which determines their mol­ecular geometries. Compound (I) crystallizes in the monoclinic space group P21/c. It has one thio­phene ring disordered over two positions, with a minor component contribution of 0.100 (3). Compound (II) crystallizes in the noncentrosymmetric ortho­rhom­bic space group Pca21 with two independent mol­ecules in the unit cell. These mol­ecules are related by a noncrystallographic pseudo-inversion center and possess very similar geometries. The crystal packings of (I) and (II) have a topologically common structural motif, viz. stacks along the b axis, in which the mol­ecules are bound by weak C—H⋯O hydrogen bonds. The noncentrosymmetric packing of (II) is governed by attractive inter­molecular Br⋯Br and Br⋯N inter­actions, which are also responsible for the very high density of (II) (1.861 Mg m−3).
doi:10.1107/S0108270109008336
PMCID: PMC2665971  PMID: 19346612

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