H. Hartung

Banana-shaped or rod-like mesogens? Molecular structure, crystal structure and mesophase behaviour of 4,6-dichloro-1,3-phenylene bis[4-(4-N-subst.-phenyliminomethyl) benzoates]

Abstract Terminally alkyl- and alkyloxysubstituted 4,6-dichloro-1,3-phenylene bis[4-(phenyliminomethyl)benzoates] have been synthesized and studied by optical microscopy, differential scanning calorimetry, NMR spectroscopy, X-ray diffraction and dielectric measurements. Surprisingly, nematic and smectic phases are observed, although comparable bisesters of resorcinol and monochlororesorcinol exhibit B phases typical for banana-shaped mesogens. It could be proved by NMR investigations in the liquid crystallinen state that the molecules have a nearly rod-like shape. Dielectric measurements indicate a rotation around the molecular long axis as known from calamitic mesogens, which is clearly distinguished from the behaviour of bent molecules. Obviously, substitution of the central phenyl ring of the bent 1,3-phenylene bis[4(4-n-alkyloxyphenyliminomethyl)benzoates] by two chlorine atomas causes a markedly change of the molecular shape resulting in nearly calamitic mesogens. These results are supported by singl...

Crystal and Molecular Structure of the Nematogenic Compound 4′-Cyanophenyl-4-n-Pentoxybenzoate

Abstract The title compound with the formula C5H11O-C6H4-COO-C6H4-CN (CPPOB) crystallizes in the orthorhombic space group Pnam with a = 16.465 A, b = 13.577 A, c = 7. 621 A and four molecules per unit cell. The structure has been solved by direct methods and refined to a final R value of 0.050. The CPPOB molecules have exact Cs symmetry as a consequence of their location on crystallographic mirror symmetry planes, the benzene ring to which the cyano group is attatched has a perpendicular orientation to the other ring in the plane. The molecules adopt a nearly optimal stretched form, neighbouring molecules make an angle of 35.2°. The results are discussed in relation to the mesomorphic behaviour of CPPOB.

Electrophilic Cyclisation of Bis(4-methoxybenzylthio)acetylene − Competition Between Ar2-6 and Ar1-5 Routes, Yielding 1H-2-Benzothiopyrans or Spiro Derivatives of Cyclohexadienone

Treatment of bis(4-methoxybenzylthio)acetylene (1) with iodine monochloride yields different products in the presence or absence of nucleophiles such as water or alcohols. Normally, the electrophilic cyclisation of bis(benzylthio)acetylenes produces 1H-2-benzothiopyrans 2 by intramolecular ortho attack on the aromatic ring by a vinyl cation formed in situ (Ar2-6 cyclisation). In the case of 1, however, the high electron density in the ipso position of the aromatic ring favours ipso attack (Ar1-5 route). The fate of the ipso σ complex is determined by the presence or absence of nucleophiles in the reaction medium. When nucleophiles are excluded, the σ complex is stabilised by 1,2-migration and formation of 1H-2-benzothiopyran 2a. In the presence of water, the σ complex yields spirocyclohexadienone dihydrothiophenes 3a and 3d. In the presence of 3-methylbenzyl alcohol, the methoxy substituent of the 2-benzothiopyran ring is exchanged by the 3-methylbenzyloxy group in product 2d. These findings are consistent with the formation of 2a, 2c, 2d and 2f by ipso − and not ortho − attack on the 4-methoxyphenyl ring. Similar results were obtained both with ICl and from a proton-induced cyclisation. In one-pot syntheses, 3a and 3d were transformed into 2-benzothiopyrylium salts 4a and 4b by tritylium tetrafluoroborate, and 3a and 3b were rearranged into the 6-hydroxy-substituted 2-benzothiopyrans 2b and 2g by proton catalysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The Crystal and Molecular Structure of 4'-Cyanophenyl-4-n-Pentylbenzoate

Abstract The crystal and molecular structure of the title compound with the formula C5H11—C6H4—COO—C6H4—CN (CPPB) has been determined by X-ray diffraction methods. CPPB crystallizes in the monoclinic space group P21/n with eight molecules in a unit cell of dimensions a = 15.268(2) A, b = 9.165(1) A, c = 24.031(3) A, β = 94.67(1)°. The structure has been solved by direct methods and refined to an R value of 0.070. The CPPB molecules adopt a stretched form and are packed in an approximate parallel imbricated mode, the molecular long axes making an angle of about 5° with the crystal c axis. The molecular geometry and packing are discussed in relation to the mesomorphic behavior of CPPB.

Di(5-substituted-salicylidene)ethylene diaminato-Complexes (Part II). Mesomorphic Properties of Di(5-alkylsalicylidene)ethylene diaminato Nickel(II) and Copper(II) Complexes and an X-Ray Structure Determination of Di(5-hexyloxy salicylidene)ethylenediaminato Nickel(II)

Abstract Di(5-alkylsalicylidene)ethylenediaminato nickel(II) and copper(II) complexes have been synthesized and investigated. They show similar behaviour to the corresponding alkyloxy-substituted complexes—wide mesophase ranges and calamitic smectic phases. The thermal stability of the nickel(II) complexes is higher than that of the copper(II) complexes. The title compound crystallizes with one water molecule per formula unit (water—diethyl ether interface) and Z = 4 in space group P21/c. X-ray crystal structure analysis shows that the molecular skeleton with the exception of the ethylene bridge is essentially planar and adopts a maximum stretched form. The crystal packing is characterized by a herringbone arrangement of columns of centrosym- metrical pairs of molecules.

Reactivity and crystal and molecular structure of 5-phenyl-5-phospha-2,8-dithia-1-stanna(II)bicyclo[3.3.o1,5]octane

Abstract 5-Phenyl-5-phospha-2,8-dithia-1-stanna(II)bicyclo[3.3.o1,5]octane (1) was prepared in good yield by the reaction of tin(II) butoxide with the appropriate mercaptophosphane in toluene. Its crystal and molecular structure was determined by X-ray analysis. Compound 1 crystallizes in the rhombohedral space group R3, with 9 molecules in a unit cell of dimensions (referred to hexagonal axis) a 17.218(5) A, c 10.859(3) A, and V 2787.9 A3. The structure was solved by the Patterson method, and full-matrix least-squares refinement led to a final R value of 0.026. The crystal structure is characterized by parallel infinite spiral chains built up of molecules connected by Sn … S intermolecular contacts of 3.31 A. The molecules exhibit a strongly distorted ψ-trigonal bipyramidal geometry around the tin atom with the phosphorus atom in an equatorial position and an SnP distance of 2.61 A The eight-membered ring adopts a boat—boat conformation. The reaction of compound 1 with Cr(CO)6 in THF under UV irradiation yields the corresponding chromium pentacarbonyl complex.

Unexpected reaction of [Ni(CO)4-n(R2PCl)n] (n = 1, 2 ; R = But, Cy, Ph) with Na2[Fe2(CO)8]. Synthesis and electronic structure of the anions [Fe2(μ-CO)(CO)6(μ-PR2)]- and their reactions with H+ and [M(PPh3)]+ (M = Cu, Ag, Au)

Treatment of [Ni(CO)4-n(R2PCl)n] (n = 1, 2; R = Bu(t), Cy, Ph) with Na2[Fe2(CO)8] gave, depending on n and R, either the doubly phosphido-bridged complexes [Fe2(CO)6(mu-PR2)2] or the anions [Fe2(mu-CO)(CO)6(mu-PR2)]-. These anions can also be obtained by the reaction of [Fe(CO)4(PR2)]- with either [Fe2(CO)9] or [Fe(CO)5] via the intermediate [Fe2(CO)8(mu-PR2)]-. The electronic structure of the anions [Fe2(mu-CO) (CO)6(mu-PR2)]- has been studied by an EHT calculation which supports their ambident oxygen- or metal-nucleophilicity. The metal-centred nucleophilic reactions of the anion [Fe2(mu-CO)(CO)6(mu-PBu(t)2)]- with H+ and [M(PPh3)]+, (M = Cu, Ag, Au), respectively, are described. The new complexes have been characterized by various spectroscopic methods and the structure of [Fe2{mu-Ag(PPh3)}(mu-CO)(CO)6(mu-PBu(t)2)] has been established by X-ray analysis.

Crystal and molecular structure of mesogenic 4-ethoxy-3′-(4-ethoxy-phenyliminomethyl)-4′-(4-methoxy-benzoyloxy)azobenzene

Abstract 4-Ethoxy-3′-(4-ethoxy-phenylimino-methyl)-4′-(4-methoxy-benzoyloxy)-azobenzene (EEMA) exhibits liquid crystalline behaviour despite the strong deviation of the molecule from both rod-like and disc-like shape. In order to obtain further information about EEMA the compound was resynthesized and a single-crystal X-ray analysis was performed. EEMA crystallizes in the triclinic space group P1 with two molecules per unit cell. The structure was solved by direct methods and refined to R = 0.058 (Rw = 0.055) for 2473 observed reflections. The EEMA molecule has a bifurcated shape. The phenyliminomethyl branch is bent markedly from the nearly linear three-ring basic fragment but is almost coplanar with the azobenzene moiety. The molecular conformation is apparently affected by an intramolecular interaction of the carboxylic and azomethine group (close C … N contact distance of 2.783(5) A). The molecular packing in the crystal can be described in terms of a sheet structure with interdigitating comb-like row...

Synthesis of [Mo2{μ-Au(PPh3)}Cp2(CO)4(μ-PPh2)] and structural comparison with the dimolybdenum complexes [Mo2Cp2(CO)4(μ-H)(μ-PPh2)] and PPN[Mo2Cp2(CO)4(μ-PPh2)] (PPN = (PPh3)2N+)

Abstract [Mo 2 {μ-Au(PPh 3 )}Cp 2 (CO) 4 (μ-PPh 2 )] ( 4 ) has been synthesized from K[Mo 2 Cp 2 (CO) 4 (μ-PPh 2 )] ( 2 ) and [AuCl(PPh 3 )] and characterized by IR and 31 P NMR spectroscopy. X-ray structures of this cluster and of [Mo 2 Cp 2 (CO) 4 (μ-H)(μ-PPh 2 )] ( 1 ) and PPN[Mo 2 Cp 2 (CO) 4 (μ-PPh 2 )] ( 3 ) have been performed and refined to R = 0.026, 0.037 and 0.025, respectively. In all three complexes two MoCp(CO) 2 fragments are bridged by a PPh 2 group and they are additionally bridged by a hydrogen atom or an AuPPh 3 group in 1 and 4 . The most striking difference in the structures of the doubly-bridged complexes involves the conformation of the central Mo 2 PAu/H unit: it is approximately planar for 1 but strongly folded for 4 .

Molecular structure and stereoisomerization of bis(2-dimethylchlorostannylethyl)phenylphosphine oxide

Abstract NMR data ( 1 H, 13 C, 119 Sn, 31 P) have revealed that in donor-free solvents bis(2-dimethylchlorostannylethyl)phenylphosphine oxide ( 1 ) has a symmetric bicyclic structure with the two tin atoms intramolecularly coordinated to the PO group. In the presence of pyridine one intramolecular PO → Sn coordination is broken and the fifth coordination site of the corresponding tin atom occupied by a solvent molecule. In both solvents compound 1 undergoes various ligand exchange processes. The crystal structure of compound 1 has been determined by X-ray analysis and refined to a final R value of 0.047. The compound crystallizes in the monoclinic space group P 2 1 / c . The structure consists of monocyclic units involving an intramolecular PO → Sn coordination which are associated through intermolecular SnCl … Sn bridges to give infinite zigzag chains parallel to the b -axis. The ligand polyhedra of the two tin atoms exhibit trigonal-bipyramidal geometry, with different deviations from the ideal trigonal-bipyramidal arrangement.