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Formation and Characterization of Melam, Melam Hydrate, and a Melam–Melem Adduct

Authors

  • Eva Wirnhier,

    1. Department of Chemistry, University of Munich (LMU), Butenandtstrasse 5-13 (D), 81377 München (Germany), Fax: (+49) 89-2180-77440
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  • Maria B. Mesch,

    1. Chair of Inorganic Chemistry III, University of Bayreuth, Universitätsstrasse 30, 95447 Bayreuth (Germany)
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  • Prof. Dr. Jürgen Senker,

    1. Chair of Inorganic Chemistry III, University of Bayreuth, Universitätsstrasse 30, 95447 Bayreuth (Germany)
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  • Prof. Dr. Wolfgang Schnick

    Corresponding author
    1. Department of Chemistry, University of Munich (LMU), Butenandtstrasse 5-13 (D), 81377 München (Germany), Fax: (+49) 89-2180-77440
    • Department of Chemistry, University of Munich (LMU), Butenandtstrasse 5-13 (D), 81377 München (Germany), Fax: (+49) 89-2180-77440
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Abstract

Until recently, melam, [C3N3(NH2)2]2NH, has been regarded as a short-lived intermediate in the condensation process of melamine that is only detectable under special reaction conditions owing to its high reactivity. A new synthetic approach has allowed a closer look at the formation and condensation behavior of melam by using elevated ammonia pressure in autoclaves. Whereas the thermal treatment of dicyandiamide at 450 °C and 0.2 MPa ammonia yielded melam in large amounts, prolonged treatment under these conditions (9 days) led to the formation of a melam–melem adduct, thus enabling the first insight into the condensation process of melam into melem. The hydrothermal treatment of melam at 300 °C (24 h) yields melam hydrate, [C3N3(NH2)2]2NH2 H2O (space group P21/c; a=676.84(2), b=1220.28(4), c=1394.24(4) pm; β=98.372(2)°; V=1139.28(6)×106 pm3; Z=4), which crystallizes as a layered structure that is composed of almost-planar melam molecules, thereby forming ellipsoidal rosette-like motifs. The resulting voids are filled with four water molecules, thus forming a dense network of hydrogen bonds.

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