Anke Schwarzer

Supramolecular control of fluorinated benzophenones in the crystalline state

Crystal structures of three fluorinated benzophenones were determined via single crystal X-ray diffraction. The occurrence of the C–F⋯H, F⋯F, C–F⋯πF interactions in these crystal structures indicates that a base limit of fluorine atoms in the molecule seems to be necessary for successful competition with the hydrogen type of interactions.

Use of melem as a nucleophilic reagent to form the triphthalimide C6N7(phthal)3--new targets and prospects.

Melem (1), as one of the most important representatives of the tri-s-triazine compounds, can be used as a nucleophilic reagent in reactions with phthalic acid derivatives. The synthesis of 2,5,8-triphthalimido-tri-s-triazine (C(6)N(7)(phthal)(3), 2) was investigated starting from phthalic anhydride or phthalic dichloride in various solvents, at different temperatures as well as in the solid state. NMR measurements (solution and solid state), IR spectroscopy and elemental analysis indicated the formation of a cyclic imide. Single-crystal structure analysis of a 1:1 adduct of 2 with nitromethane proved the molecular structure expected for a phthalimido-s-heptazine. DFT calculations were performed to obtain a better insight into the structural features of compound 2, especially the interaction of the carbonyl groups with the tri-s-triazine nitrogen atoms. The title compound 2 shows promising properties: it is thermally stable up to 500 °C in air and shows strong photoluminescence with a maximum emission at around 500 nm. The potential of the nucleophilic reaction of melem with other strong electrophiles provides new targets and prospects.

A series of aryl-/alkyl-substituted melems

Four different tri-s-triazines were synthesized bearing one, two or three substituents NEt2 and/or NPh2 by reaction of cyameluric chloride and the corresponding amines. All compounds were characterised comprehensively including single crystal structure analysis, NMR, FT-IR and elemental analysis.

Precursors for pyromellit-bridged silica sol–gel hybrid materials

Bridged bis(trialkoxysilylalkyl)pyromellitic diimides 3–6 were prepared as single-source precursors for sol–gel derived organic–inorganic hybrid materials. The synthesis route starts with the formation pyromellit diimide 1 from pyromellitic dianhydride and hexamethyldisilazane (HMDS), followed by metallation of the NH groups to give the dipotassium salt 2. The four molecular hybrid precursors 3–6 were obtained according to the first step of the Gabriel synthesis. The reaction rates were studied as a function of the alkyl chain length and the nature of the halide (Cl vs. I). All products 1–6 were comprehensively analysed using FT-IR, 1H and 13C NMR spectroscopy as well as elemental analysis, and – in the case of 3–6 – also with 29Si NMR spectroscopy. For compounds 3 (with propylene groups and methoxy substituents) and 6 (with methylene groups and ethoxy substituents) single crystal X-ray structures were determined and discussed. Hydrolysis and condensation of the alkoxides 3–6 were carefully monitored with solution 29Si and 1H NMR spectroscopy providing a basis for further studies on the formation of silica-pyromellit organic–inorganic hybrids from precursors 3–6. Finally the formation of flexible and transparent hydride films using precursors 4 and 6 was proved.

Reactions of CO2 and CO2 Analogs (CXY with X, Y = O, S, NR) with Reagents Containing Si–H and Si–N Units

Abstract This review covers the literature on reactions of CO 2 , isoelectronic molecules, like carbonyl sulfide COS, and carbon disulfide CS 2 , and other heterocumulenes, like isocyanates and isothiocyanates, with aminosilanes and hydridosilanes, that is, compounds with Si–N and Si–H units. The state of the art in this field is compared with our own investigations. In many cases, the CO 2 insertions into Si N bonds proceed exothermically providing good to very good yields of the products. In some cases, the insertion reactions have been reported to be reversible, while in other cases, stable and useful products are obtained that have diverse applications in industry, for example, as RTVs (room temperature vulcanizers), for the synthesis of siloxanes, N , N ′-disubstituted ureas or isocyanates. Reactions of CS 2 and COS with Si–N and Si–H units provide mono -insertion products as well. Isocyanates do not result in the Si O-bonded compounds but Si N moieties are formed. The latter products obtained from isocyanates and isothiocyanates can be utilized as modifiers or precursors for polymers, hybrid, and ceramic materials.

Crystal structures of benzil monoximes controlled through configurational isomerism, molecular substitution and external complexation

Crystal structures of the configurational isomers of benzil monoxime (1 and 2), a p-methoxy derivative (3) and its solvated species with triethylamine (3a) are reported showing specific influences of the molecular configuration, substitution and solvation on the conformational property and packing behaviour of the molecules. Based on the observed interdependences, in particular involving modes of interaction, potential utilization of the 1,2-dione monoxime functional unit for the purpose of crystal engineering seems promising.

Conformations of benzene-based tripodal isatin-bearing compounds in the crystalline state

Single crystal X-ray diffraction allowed the identification and characterization of new solvates of tripodal trimethylbenzene- and triethylbenzene-based compounds bearing 1H-indole-2,3-dione (isatin) groups. Both unsubstituted and methyl or methoxy substituted isatins were used as building blocks for the construction of the host molecules 1–6. Four different conformations of 1–6 have been observed in the crystal structures, which differ not only in the position of the heterocyclic side arms (above or below the central benzene ring) but also in the orientation of the carbonyl groups of the isatin units. In the case of the trimethylbenzene derivative 2, single crystal X-ray diffraction allowed the identification and characterization of three solvates (2a, 2b and 2c), two of which represent the polymorphic forms 2·CH3CN-I (2a, baa/all-out) and 2·CH3CN-II (2b, aaa/out,out,in). The crystal packings of 1–6 are characterized by the presence of C–H⋯O, C–H⋯N, C–H⋯π, π⋯π and CO⋯π interactions as well as Cl⋯Cl contacts in the case of the chloroform-containing solvates.

1-Bromo-2,3,5,6-tetra­fluoro-4-nitro­benzene

In the title compound, C6BrF4NO2, the nitro group is twisted by 41.7 (3)° with reference to the arene ring mean plane. The main interactions stabilizing the crystal structure include O⋯Br contacts [3.150 (2) and 3.201 (2) Å], while F⋯F interactions are minor [2.863 (3)–2.908 (3) Å].

5,7-Dibromo-2-methyl­quinolin-8-ol

In the title compound, C10H7Br2NO, the molecule possesses a planar geometry with an r.m.s deviation of 0.0383 Å for all non-H atoms. The crystal structure displays O—H⋯N and C—H⋯O hydrogen bonding, as well as Br⋯Br contacts [3.6284 (4) Å].

Supramolecular behaviour of bulky arylboranes in the crystalline state

The aromatic monoboranes 1, 2 and bisboranes 3, 4 of which 4 is a newly synthesised compound have been studied with reference to their supramolecular behaviour in the crystalline state. While the monoboranes crystallise purely, the bisboranes form channel-type solvent inclusions with m-xylene (3a) and nitrobenzene (4a) in the crystals, showing their potential as clathrate hosts in the realm of optically and electronically interesting compounds.