Acta Crystallographica Section B

Structural Science

Volume 55, Part 1 (February 1999)


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Acta Cryst. (1999). B55, 55-69    [doi:10.1107/S0108768198006557]

Crystal and molecular structures of diazapyrenes and a study of [bold pi]\cdots[bold pi] interactions

R. Kiralj, B. Kojic-Prodic, I. Piantanida and M. Zinic

Abstract: Two diazapyrenes, 5,10-dimethyl-4,9-diazapyrene (1) and novel 2,7-dimethyl-4,9-diazapyrene (2) have been synthesized. Their crystal structures are reported here and are the first representatives of diazapyrenes. Crystal data: (1) monoclinic, P21/c, a = 4.0246  (5), b = 15.5147  (5), c = 9.1453  (9)  Å, [beta] = 101.23  (1)°, V = 560.1  (1)  Å3, Z = 2, R = 0.043; (2) monoclinic, C2/m, a = 12.4968  (3), b = 11.4751  (4), c = 3.9615  (5)  Å, [beta] = 96.80  (1)°, V = 564.09  (5)  Å3, Z = 2, R = 0.0405. The experimental bond lengths are compared with those calculated by molecular mechanics (MM3), semi-empirical methods (MOPAC6.0-PM3, AM1, MNDO) and values predicted by valence-bond and variable-electronegativity self-consistent field (VESCF) methods. [bold pi]\cdots[bold pi] interactions in (1), (2) and seventeen other pyrene and pyrene-like molecules selected from the Cambridge Structural Database [Allen & Kennard (1993). Chem. Des. Autom. News, 8, 131-137] have been studied. The following quantitative parameters of [bold pi]\cdots[bold pi] interactions have been calculated: the shortest crystallographic axis, the offset parameter, the interplanar angle, the interactive volume and the overlapping surfaces. They are used for the classification of crystal-packing motifs; a high predominance of [beta] and a few cases of [bold gamma] and sandwich-herringbone types are observed. In addition, electronegativity, the sum of partial atomic charges of the ring non-H atoms and the number of aromatic skeleton electrons are used as parameters for classification. MOPAC-PM3 was used to calculate the partial atomic charges in (1), (2) and pyrene analogues. Correlations between geometrical and electronic structure parameters reveal an analogy between the [beta]-type structures and the crystal structure of graphite.

Online 1 February 1999

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