摘要:

AbstractThe optical symmetry of many crystals is lower than would be expected from their external form and X‐ray diffraction data. Recently suchoptical anomalieshave been attributed to nonequilibrium structures resulting from kinetically controlled crystal growth. Impurities are incorporated to different extents at various surface sites that would otherwise have become symmetry‐related within the bulk crystal. After their discovery by Brewster in 1815, optically anomalous crystals were the subject of lively debate throughout the 19th century among some of the most distinguished contributors to the development of crystallography including Biot, Berzelius, Herschel, Mitscherlich, Frankenheim, Pasteur, Mallard, Klein, Groth, Wyrouboff, Barlow, Brauns, Rinne, Pockels, and Friedel. From a sea of wild speculation two conflicting postulates emerged: that the symmetric form resulted from accidental twinning of segments with lower symmetry, or that the optical peculiarities resulted from stress due to impurities or external perturbations. Neither postulate expresses the present view. Interest in this research waned at the turn of the century, and after 1917 no one pursued Tammann's alternative correct insight. The problem of anomalous double refraction attracted no attention for more than half a century until its recent solution. This review discusses both mineral and organic systems with particular emphasis on the phyllosilicate apophyllite and on 1,5‐dichloro‐2,3‐dinitrobenzene. These nonequilibrium structures relate to questions of crystal order, crystal growth, molecular recognition, and the design of new materials. The review provides a reminder of the enduring value of the polarizing microscope as a research tool in

ISSN:0570-0833    

DOI:10.1002/anie.199200013

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe synthesis of Cycloalkadiynes with medium‐sized rings may be accomplished by a number of ring‐closing and elimination reactions. Information concerning the conformation of the rings as well as the extent of transannular interaction between the triple bonds is obtained by analysis of X‐ray crystallographic data and by photoelectron spectroscopy. The diacetylene complexes of Ag1and Cu1show hardly any structural change compared to the uncomplexed compounds while the bis(hexacarbonyldicobalt) complexes differ significantly in their structural parameters. Reaction of Cycloalkadiynes with dicarbonyl(η5‐cyclopentadienyl)cobalt yields inter‐ and intramolecular cyclobutadiene complexes. The superphane of cyclobutadiene formed by the intermolecular reaction can be transformed into a number of highly strained cage compounds in few steps. In addition, the variety of such cage compounds can be increased if the reaction of a cyclic diacetylene is carried out with dimethylacetylenedicarboxylate in the presence of aluminum chloride. The intermediate bridged Dewar benzenes eventually lead to propell

ISSN:0570-0833    

DOI:10.1002/anie.199200271

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200451

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200471

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200491

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200521

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200541

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200561

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200581

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199200591

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY