Halide anion-templated assembly of di- and triiodoperfluorobenzenes into 2D and 3D supramolecular networks Gabriella Cavallo a , Serena Biella a,b , Jian Lu ¨ a , Pierangelo Metrangolo a,b, *, Tullio Pilati c , Giuseppe Resnati a,b,c, **, Giancarlo Terraneo a,b a NFMLab - D.C.M.I.C. ‘‘Giulio Natta’’, Politecnico di Milano, Via L. Mancinelli 7, 20131 Milan, Italy b CNST - IIT@POLIMI, Politecnico di Milano, Via G. Pascoli 70/3, 20133 Milan, Italy c C.N.R. - I.S.T.M., University of Milan, Via C. Golgi 19, 20133 Milan, Italy 1. Introduction Interactions involving halogen atoms as electrophilic species (Lewis acid) have been named halogen bonding (XB) [1] to highlight the similarities they share with the hydrogen bonding (HB) in which an electropositive hydrogen atom functions as electron-acceptor. In fact, the electron density distribution around monovalent chlorine, bromine, and iodine atoms is highly anisotropic and an electroposi- tive region (s-hole) frequently exists on the extension of the covalent bond [2]. This electropositive crown is surrounded by an electroneutral ring and, further out, an electronegative belt. Halogen atoms can thus work as electron-donors in directions perpendicular to the covalent bond (at the electronegative belt) and as electron- acceptors on the extension of the covalent bond (at the electroposi- tive crown). XB is a strong and specific interaction and, as a consequence of the anisotropic distribution of the electron density around halogen atoms, also directional enough to be particularly effective in geometry-based design and supramolecular construc- tion. Molecular iodine is known to function as an effective electrophilic species (XB-donor) since mid-nineteen century and a large variety of molecular complexes involving iodine have been obtained on its self-assembly with electron-donors (Lewis bases) [3]. However, the variety of electron-donors which can be paired with iodine is limited by its low reduction potential. Moreover, while with weak electron-donors iodine functions as a bidentate electron- acceptor, with stronger Lewis bases (e.g. some nitrogen hetero- cycles) the polarization of the I 2 molecule is increased to the point that interaction occurs at only one of the iodine atoms [4]. This electron density transfer from one iodine to the other may even result in amphoteric behaviour of I 2 molecules, with the second iodine atom serving as a Lewis base towards another I 2 molecule and forming neutral polyiodine systems [5]. Organic polyiodides are less prone than I 2 to oxidize sensitive donors and they are also more robust and predictable than I 2 in the Journal of Fluorine Chemistry 131 (2010) 1165–1172 ARTICLE INFO Article history: Received 4 April 2010 Received in revised form 13 May 2010 Accepted 13 May 2010 Available online 11 June 2010 Keywords: Fluorobenzene Halide anions Halogen bonding Self-assembly Crystal engineering Supramolecular chemistry Dedicated to Professor Russell P. Hughes on the occasion of receiving the 2010 ACS Award for Creative Work in Fluorine Chemistry. ABSTRACT The single crystal structures of five co-crystals formed by the reaction of different iodide and bromide salts with di- and triiodoperfluorobenzenes (I-ArF) are reported. All of these perfluorocarbon- hydrocarbon systems are heteromeric three-component systems, wherein the weakly coordinating cations favour the formation of naked halides, which function as electron-donors towards the I-ArF modules. The analysis of the crystal structures shows that I  I–ArF, and Br  I–ArF halogen bonds (XBs) control the self-assembly of the obtained supramolecular architectures. 2D and 3D supramolecular networks have been obtained, wherein naked iodide and bromide anions act as tri-, tetra-, or pentadentate nodes. The selected examples demonstrate that I-ArF modules can be particularly robust and reliable tectons for XB-based coordination of halide ions and afford supramolecular architectures in a rational and predictable way. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author at: Dipartimento di Chimica, Materiali ed Ingegneria Chimica ‘‘Giulio Natta’’, Politecnico di Milano, Via L. Mancinelli 7, 20131 Milan, Italy. Tel.: +39 02 2399 3041; fax: +39 02 2399 3180. ** Corresponding author at: NFMLab - D.C.M.I.C. ‘‘Giulio Natta’’, Politecnico di Milano, Via L. Mancinelli 7, 20131 Milan, Italy. Tel.: +39 02 2399 3032. E-mail addresses: pierangelo.metrangolo@polimi.it (P. Metrangolo), giuseppe.resnati@polimi.it (G. Resnati). Contents lists available at ScienceDirect Journal of Fluorine Chemistry journal homepage: www.elsevier.com/locate/fluor 0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2010.05.004