Perfluorocarbon-Hydrocarbon Self-Assembly: Part X = InteractionsattheOutsideFacesofCalix[4]arenes: Two-DimensionalInfiniteNetworkFormationwithPerfluoroarenes MariaT.Messina, [a] PierangeloMetrangolo, [a] SebastianoPappalardo, [b] MelchiorreF.Parisi, [c] TullioPilati, [d] andGiuseppeResnati* [a] Abstract: Attractive p ± p interactions between two of the four outside cavity faces of 1,3-bis-pyridylmethylcalix[4]ar- ene (1) and both faces of 1,4-diiodote- trafluorobenzene (2a) form infinite one- dimensional non-covalent ribbons where the two modules alternate. These rib- bons are cross-linked by electron do- nor±acceptor interactions between pi- colyl nitrogen atoms of calixarene 1 in one chain and iodine atoms of perfluor- oarene 2a in another chain and the two- dimensional supramolecular network 3a is formed. A similar behaviour is also shown by 1,4-dibromotetrafluoroben- zene (2b). The halogen bonding and the attractive p ± p interactions occur in directions which are nearly orthogonal each other. Diiodotetrafluorobenzene, being involved in both these interac- tions, appears to be a particularly inter- esting tecton. The ability of electron- poor arenes to elicit the exo-receptor potential of calixarene module by con- necting their outside faces through p ± p interactions may be developed as a new and general binding protocol in calixar- ene self-assembly processes. Keywords: calixarenes ´ donor±ac- ceptor systems ´ host±guest chem- istry ´ supramolecular chemistry Introduction Recent developments in the host ± guest chemistry and in the supramolecular chemistry of calix[n]arenes have definitely shown the great potential of these compounds both in recognition processes and in the construction of highly organised and complex architectures. [1] Calixarenes have frequently been used as versatile plat- forms for the covalent insertion of appendages which drive self-assembly processes by using weak forces such as hydro- gen bonds, [2] co-ordination bonds, [3] and van der Waals interactions. [4] However, in most cases, calixarenes have been used as endo-receptors [5] (concave molecules), a role they are perfectly tailored to by the cone conformation they frequently adopt. A wide variety of metal cations (alkaline, alkaline earth, transition metal, lanthanide cations) have been com- plexed in the solid state and in solution and the ion has invariably been included in the calixarene cavity region. [6] Neutral molecules, as diverse as toluene, acetonitrile, acetone and water, have also been included in the solid state within the calixarene cavity. [1c,d, 7] By connecting two or more calixarene units into larger assemblies such as carcerands and holands, cavities of nanosize dimensions have been formed hosting even molecular clusters [8] and molecules as large as the fullerene. [9] The p-basic character of the cavity significantly contributes to the ability of calixarenes to work as effective host molecules in inclusion and recognition processes. The attractive cation ´´´ p, [10] C-H ´´´ p, [11] and O-H ´´´ p [12] interac- tions which determine, or at least favour, the binding of the guest involve the calixarene aromatic ring faces directed inside the cavity. To the best of our knowledge, the outside faces of calixarene rings have worked as p-basic motifs (exo- receptors) [5] only towards transition metal derivatives and very few cases of this behaviour have been reported. [13] Here we describe the first case where calixarenes work as exo-receptors (convex molecules) of neutral molecules. Spe- cifically, calixarene 1 forms infinite chains with perfluoroar- ene 2a (Scheme 1) as the calixarene phenol ring faces directed [a] Prof. Dr. G. Resnati, Dr. M. T. Messina, Dr. P. Metrangolo Dipartimento di Chimica, Politecnico di Milano 7, via Mancinelli, 20131 Milano (Italy) Fax: ( 39)02-23993032 E-mail: resnati@dept.chem.polimi.it [b] Prof. S. Pappalardo Dipartimento di Scienze Chimiche, Universita Á di Catania 6, viale Andrea Doria, 95125 Catania (Italy) [c] Dr. M. F. Parisi Dipartimento di Chimica Organica e Biologica Universita Á di Messina, 31, Salita Sperone, 98166 Messina (Italy) [d] Dr. T. Pilati C.N.R.±Centro Studio Relazioni Struttura Reattivita Á Chimica Universita Á di Milano, 19, via Golgi, 20133 Milano (Italy) [ = ] For part IX see ref. [17a]. FULL PAPER Chem.Eur.J. 2000, 6, No. 19  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0947-6539/00/0619-3495 $ 17.50+.50/0 3495