| | 1 | Author
| Z. Naturforsch | Requires cookie* | | | Title
| Die unterschiedlichen Strukturen des im Kristall verdrillten 1,4-Bis(tricyanvinyl)- benzols sowie des eingeebneten 1-Tricyanvinylbenzols, Dichtefunktional- Berechnungen und cyclovoltammetrisch sowie ESR/ENDOR-spektroskopisch charakterisiertes Reduktionsverhalten  | | | | Abstract
| In te ra c tio n s in M o le cu lar C rystals, 127 [1] T h e D iffe re n t S tru c tu re s in th e C rystal o f T w isted l,4 -B is(tric y a n o v in y l)b e n z e n e as w ell as o f P la n a r 1-T ricyanovinyl-benzene, D e n sity F u n c tio n a l C a lc u la tio n s a n d R e d u c tio n B e h a v io u r S tu d ie d by C y c lo v o ltam m e try a n d E S R /E N D O R S p ec tro sc o p y H a n s B o c k 3*, W olfgang S eitz3, N o rb e rt N a g e l3, R ü d ig e r B a u rb, Jan W. B a ts3, Z d e n e k H a v la sc, R o d n e y F. C. C la rid g e d The attem pted crystal growth of l,4-bis(tricyanovinyl)benzene dianion salts, although wi thout success so far, has provided information of general interest. The crystal structures of the related mono and l,4-bis(tricyanovinyl)benzene derivatives differ considerably in their substituent group twisting angles: The two tricyanovinylbenzenes in split-positions exhibit dihedral angles of only 6° or 11°, whereas the two C2(CN)3 groups of the disubstituted benzene are conrotationally twisted by 48° out of the benzene plane. Density functional calculations with 6 -3 1 1 ++G** basis sets, however, predict identical values of 32° for both com pounds and, therefore, their crystal arrangements are discussed in detail for packing-enforced additional interactions. Cyclovoltammetric and ESR /EN D O R -m easurem ents pro vide inform ation on the redox behaviour, a prerequisite for attem pts to crystallize molecular anion salts: The 1,4-disubstituted derivative with a cyclovoltammetrically determ ined half wave reduction potential of +.14 V in aprotic TH F solution proves to be one of the strongest polycyano-substituted ^--acceptors and its radical anion can be selectively generated by T1 metal reduction as confirmed by its ESR/EN D O R spectra. Wechselwirkungen in Molekülkristallen, 127 [1] Ausgangspunkte | | | |
Reference
| Z. Naturforsch. 52b, 1125—1138 (1997); eingegangen am 2. Juni 1997 | | | |
Published
| 1997 | | | |
Keywords
| Tricyanovinyl Benzene Derivatives, Crystal Structure, Density Functional Calculations | | | |
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| 52 | |
| 2 | Author
| M. Weisser, W. Weyrich | Requires cookie* | | | Title
| The Electronic Structure of Hydrogen Bonding in a-Oxalic Acid Dihydrate | | | | Abstract
| Compton spectra of a-oxalic acid dihydrate single-crystal slices and powder samples were mea-sured in a helium atmosphere using 59.537 keV 241 Am radiation. In the anisotropic case, the scattering vector was oriented parallel to the shortest hydrogen bond, in the direction of the C = O bond, parallel to the C — O bond and perpendicular to the (a, c)-plane. The comparison of theoretical reciprocal form factors, calculated with a local density-approximation (LDA) method for an a-(COOH) 2 • 2H 2 0 cluster in triple-zeta basis-set quality, with the experimental data has demon-strated that there is a considerable influence of intermolecular interactions on the electronic struc-ture. Further calculations including the intermolecular interactions of the first coordination sphere by symmetrical orthogonalisation of the LDA wave functions clearly improved the agreement of experiment and theory. A theoretical analysis of the reciprocal form factor B a (s) in the direction of the three different hydrogen bonds of a-oxalic acid dihydrate on the basis of the cluster calculations has shown that in the region above s = 1.9 Ä all these bonds are dominated by electrostatic attrac-tion and exchange repulsion of the donor and the acceptor system. | | | |
Reference
| Z. Naturforsch. 48a, 315—324 (1993); received January 28 1993 | | | |
Published
| 1993 | | | |
Keywords
| a-Oxalic acid dihydrate, Compton spectroscopy, Hydrogen bonding, Reciprocal form factor, Density functional calculations | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0315.pdf | | | | Identifier
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| 48 | |
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