Arenediazonium Salts as Versatile (meso-Ionic) Tectons. Charge-Transfer Intercalates and Clathrates in Unusual Crystalline Networks Self-Assembled with Neutral Aromatic π-Donors
American Chemical Society
Crystal Growth and Design
Arenediazonium salts as tectonic building elements for crystal engineering possess a unique array of binding properties, including (a) strong acceptor affinity toward electronegative or neutral σ-donors; (b) enhanced C−H acidity for extensive formation of C−H···X bonds; and (c) π-acceptor properties of the electron-deficient arene substituent for charge-transfer complex formation with appropriate aromatic π-donors. Shown: Donor/acceptor intercalate in the layered structure of 3,5(NO2)C6H3N2+ BF4- with naphthalene.
The surprisingly uniform crystal packings of various arenediazonium salts (ArN2+X-) largely consist of two-dimensional ionic layers from various (N2+···X-) interactions coupled with a series of antiparallel arrays of pendant aryl groups (Ar). This crystalline architecture can be deliberately modified by the introduction of different (neutral) aromatic π-donors. On the basis of the exceptional electron-acceptor strength of the (N2+) group, the principal crystal-forming interactions of the arenediazonium tecton can be dissected into (a) strong coordination to anionic and electron-rich (neutral) σ-donors within the equatorial plane, (b) enhanced capacity for (C−H···X) hydrogen bonding, and (c) remarkable aptitude to form (noncovalent) charge-transfer bonds with aromatic π-donors. Thus, the detailed analysis of crystalline networks found in 3,5-dinitro and 4-carboethoxy derivatives of benzenediazonium salts recognizes them as remarkable intercalate and clathrate structures in which various charge-transfer interactions between the electron-deficient arene moiety and aromatic π-donors are essential for the stabilization of the unusual layered/network structures.