Interpenetrated nano-capsule networks based on the alkali metal assisted assembly of p-carboxylatocalix[4]arene-O-methyl etherw Scott J. Dalgarno,* ab Karla M. Claudio-Bosque, a John E. Warren, c Timothy E. Glass* a and Jerry L. Atwood* a Received (in Austin, TX, USA) 26th October 2007, Accepted 30th November 2007 First published as an Advance Article on the web 19th February 2008 DOI: 10.1039/b716777f Reaction of p-carboxylatocalix[4]arene-O-methyl ether with either rubidium or caesium hydroxide results in the formation of interpenetrated nano-capsule networks with the calixarene in the 1,3-alternate conformation. The formation of large capsule based assemblies with volumi- nous interiors by either introducing chemical complementarity to molecular frameworks, or by covalent/metal directed as- sembly remains a significant challenge in supramolecular chemistry. Although this is the case, a number of such assemblies have been constructed, many of which are based on various types of calix[4]arene or typically ‘bowl-shaped’ molecules, the likely reason for which is the relative rigidity of the molecular building blocks. 1 The first of the very large molecular nano-capsules to be discovered is composed of C-methylresorcin[4]arene (CMRC, 1, Scheme 1), six molecules of which assemble with eight structural water molecules to form a chiral nano-scale hydro- gen-bonded arrangement that encloses B1500 A ˚ 3 of solvent occupied space. 1a Replacement of structural water molecules by specific alcohols has recently been shown to afford an achiral version of the CMRC capsule. 1q C-Alkylpyrogallo- l[4]arenes (general notation PgCn, 2, Scheme 1) are closely related to CMRC and form analogous hydrogen-bonded nano-capsules without the need for structural water molecules due to additional ‘upper-rim’ hydroxyl groups. 1b Nano-cap- sules based on both 1 and 2 have been found to be stable in the solution phase in a number of recent studies and these nano- capsules can host various guest species of different sizes. 2 With respect to large metal–organic nano-capsule systems, we recently showed that C-propanolpyrogallol[4]arene (PgC 3 OH, 3, Scheme 1) can react with copper(II) nitrate to form a metal–organic nano-capsule (MONC) which is analo- gous to the hydrogen-bonded motif based on 2, with 24 copper centres replacing all the hydrogen atoms of the ‘upper-rim’ Pg hydroxyl groups. 1g The PgC 3 OH MONC was found to link through ‘lower-rim’ propanol tail coordination to copper centres from neighbouring capsules, rendering the material only sparingly soluble. More recently we have found that any known C-alkylpyrogallol[4]arene can be instantly reacted with methanolic copper(II) nitrate to form a precipitate of the corresponding MONC. 1t This technique can also be used to form MONC’s composed of mixed PgCn’s, and notably all of these resultant materials are highly soluble in most common organic solvents. Other recent results in this area showed that reaction of gallium(III) nitrate with short chain C-alkylpyro- gallol[4]arenes affords MONC’s in which only 12 gallium centres insert into the hydrogen-bonded seam, causing defor- mation to the motif and resulting in the introduction of structural water molecules at what can be termed ‘gates’ to the interior. 1h,l We recently expanded our interests in the area of calixarene self-assembly to include that of the p-carboxylatocalix- [n]arenes. To our knowledge, all of the large calixarene based assemblies reported to date (including those described above) have involved these molecules in the commonly observed cone conformation, and therefore result in the formation of discrete architectures. 1 In our preliminary experiments with these molecules, we found that p-carboxylatocalix[4]arene (in cone conformation) forms large diameter non-covalent nanotubes (when crystallised from pyridine) through parallel p-stacking between host molecules, as well as through the well known carboxylic acid–pyridine interaction. 3 Here we show that the Scheme 1 Diagrams of C-methylresorcin[4]arene (1), the general structure of the C-alkylpyrogallol[4]arenes (2), C-propan-3-olpyro- gallol[4]arene (3), and p-carboxylatocalix[4]arene-O-methyl ether (4) shown in the 1,3-alternate conformation. a Department of Chemistry, University of Missouri-Columbia, 601 S. College Avenue, Columbia, MO 65211, USA. E-mail: GlassT@missouri.edu. E-mail: AtwoodJ@missouri.edu; Fax: +1 573 882 2754; Tel: +1 573 882 8374 b School of Engineering and Physical Sciences-Chemistry, Heriot-Watt University, Edinburgh, UK EH14 4AS. E-mail: S.J.Dalgarno@hw.ac.uk; Fax: +44(0) 131 451 8130; Tel: +44(0) 131 451 8025 c Daresbury Science & Innovation Campus, Warrington, Cheshire, UK WA4 4AD w Electronic supplementary information (ESI) available: Figure of additional rubidium–carboxylate bonding. See DOI: 10.1039/ b716777f 1410 | Chem. Commun., 2008, 1410–1412 This journal is  c The Royal Society of Chemistry 2008 COMMUNICATION www.rsc.org/chemcomm | ChemComm