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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 649-656 
    ISSN: 0947-3440
    Keywords: Catenanes ; Interlocked rings ; Mechanical bond ; Photoswitches ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four catenanes (1-4) and the corresponding tetracationic monocycles 5-8 are synthesized. X-ray structural analyses allow a prediction of the mobility (circumrotation) of the „interlocked“ rings in the catenanes, which is proven by 1H-NMR spectroscopy. An unexpected order in the crystal packing of 6 is demonstrated. (E/Z) isomerization in one ring influences the second ring of 1-4 and inversely. An existing obstacle inside the cavity of the switchable macrocycle can block this isomerization completely.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1515-1519 
    ISSN: 0947-3440
    Keywords: Macrocycles ; Recognition ; Piperazines ; Self-assembly ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by H—C—H…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phane 8b (di-dihydrochloride salt) adopts a chair-chair conformation, confirming that protonation of the N atoms does not change the conformation.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0947-3440
    Keywords: Alkyne bridges ; Charge transfer ; Host compounds ; Molecular cavities ; Toposelectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By a mild modified Eglinton coupling a series of diynebridged macrobicyclic hosts capable of endocavital complexation were synthesized and their structures and complexation properties investigated by X-ray analysis. The inclusion of DMSO in 7 suggests a direct correlation between steric fit and orientation of the guest. On the basis of this hypothesis, the orientation of acetone in an endocavital inclusion of 2 was predicted and verified by X-ray analysis. Comparison of the single-crystal X-ray structures of the vacant macrobicycle 3 and of a family of macrobicycles showing endocavital or “pocket” complexation of neutral organic guests suggests that torsion of the cavities upon complexation results from induced fit. Hydrogenation of the triple bonds leads to the more flexible macrobicycles 10-12 with collapsable cavities. The absorption and emission spectra of the diynebridged macrobicyclic hosts 1 and 3, of their hydrogenated analogues 11 and 12, and of a hemicage parent compound of 2 (14) were investigated. The macrobicyclic compounds 3, 11, 12 and 14 exhibit a strong fluorescence in CH2Cl2 solution at room temperature. The lack of fluorescence of 2 under such conditions is attributed to the presence of low-energy charge-transfer excited states, as indicated by the charge-transfer bands in the absorption spectrum. In a rigid CH2Cl2 matrix at 77 K all the examined compounds are fluorescent.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1611-1615 
    ISSN: 0947-3440
    Keywords: Macrocycles ; Inclusion compounds ; Piperazines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New piperazine-based macrocycles with single small cavities were prepared by using high dilution technique. The inclusion of acetonitrile into the cavity (7, 8) or clathrate formation (3) was studied by 1H-NMR spectroscopy in solution and by X-ray diffraction in the crystalline state. The cycle 3 forms a molecular cleft, a molecular pocket, where the acetonitrile molecule is held by four weak N…H interactions reinforcing the clathrate formation. The cycles 7 and 8 contain a rigid cavity for an exact sterical fit with the methyl group of a linear compound like acetonitrile. The acetonitrile inclusion complex with 7 proved to be stable under normal conditions and was studied by means of thermogravimetry. It is stable up to 80°C and the breakdown is complete when the temperature is raised over 120°C. Solid-state IR studies show a shift of the cyano band of 5 cm-1 to smaller wave numbers when compared with free acetonitrile. The acetonitrile methyl group is shielded and in the 1H-NMR spectrum its signal is shifted to δ = 1.85.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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