pubs.acs.org/crystal Published on Web 08/02/2010 r 2010 American Chemical Society DOI: 10.1021/cg100737c 2010, Vol. 10 4043–4049 Serendipity in the Crystallization of a Series of C-Alkylcalix[4]resorcinarenes from Alcoholic Solvents Aaron Alexander Momose and Eric Bosch* Chemistry Department, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897. Received June 2, 2010; Revised Manuscript Received July 15, 2010 ABSTRACT: The crystal structures of a series of C-alkylcalix[4]resorcinarenes (alkyl = methyl, propyl, butyl, pentyl, hexyl, heptyl, and undecyl), each crystallized from tert-butanol, are reported. In all seven of these structures, eight tert-butanol molecules link two resorcinarenes with 16 hydrogen bonds, thereby facilitating the formation of simple dimeric hydrogen- bonded capsules, each of which encapsulates one (disordered) tert-butanol molecule as guest. These structures are compared with, and contrasted to, those obtained from the same series of resorcinarenes recrystallized both from mixed solvents containing tert-butanol and from methanol alone. Introduction The versatility of C-alkylcalix[4]resorcinarenes and their derivatives in the formation of hydrogen-bonded capsules, in which multiple resorcinarenes adopt a bowl-like conforma- tion, is well established. 1 The formation of capsules from resorcinarenes should not, however, be considered routine, as the resorcinarenes may adopt one of several nonbowl-like conformations, as amply demonstrated by a series of elegant and extensive studies. 2 Our early studies with resorcinarenes concentrated on the formation of chain-link hydrogen bonded capsules based on the self-assembly of C-methylcalix- [4]resorcinarene with bipyrimidines. 3 During the preparation of a series of resorcinarenes for an extension of that study, we encountered some difficulty in obtaining analytically pure products and found that the organic chemists standby, chro- matography, was both tedious and largely ineffective. Furthermore, repeated attempts at recrystallization from a host of single and mixed solvents were time-consuming and of limited success until we happened upon tert-butanol. Surpris- ingly, recrystallization from tert-butanol, or mixtures of tert- butanol with methanol, ethanol, or isopropanol, yielded clear colorless crystals even from highly colored solutions of the crude resorcinarenes for each of the resorcinarenes we pre- pared (see Scheme 1). Intrigued by this observation, we subjected a series of crystals to X-ray crystallographic analysis and present evi- dence herein that tert-butanol is particularly successful for crystallization/purification of C-alkylresorcinarenes, since it not only serves as hydrogen-bond acceptor and donor linking the resorcinarenes into dimeric capsules but is itself also included as a guest within the capsules. While other alcohols are clearly equally efficient as hydrogen bond accep- tors and donors, it is the size and shape of tert-butanol that is crucial for its inclusion as guest within the dimeric capsules. These observations will be compared and contrasted to other studies of the aggregation of resorcinarenes both in the solid state and in solution. Experimental Section General Procedure for the Synthesis of Calix[4]resorcinarenes. 4 Resorcinol (8.81 g, 80 mmol), aldehyde (80 mmol), and 95% ethanol (80 mL) were added to a 200 mL round-bottom flask equipped with a magnetic stir bar. The solution was sparged with argon for 15 min, and concentrated HCl (13 mL) was then added. The solution was refluxed under an argon atmosphere for 18 h and then cooled to room temperature and poured into a separatory funnel containing 80 mL of diethyl ether. 360 mL of brine was added, and the organic layer was separated, dried over magnesium sulfate, and evaporated under vacuum to produce the crude product as a yellow/brown solid. The crude product was recrystallized twice from 4:1 tert- butanol/methanol and dried at 100 °C under vacuum for 30 min to afford the calix[4]resorcinarene in more than 80% yield. Preparation of Crystals. Approximately 20 mg of the resorcinar- ene was placed in a screw cap vial and dissolved in the minimum volume of hot tert-butanol. Crystals generally began to form after several days and were harvested for X-ray analysis directly from the mother liquor. Commercially available C-methylresorcinarene (Aldrich) was also re- crystallized from tert-butanol with a small amount of methanol as cosolvent. The resultant complexes of tert-butanol with methyl-, propyl-, butyl-, pentyl-, hexyl-, heptyl-, and undecylresorcinarene respectively, are numbered 1-7, respectively. Similar procedures were used for recrystallization from mixed solvents or from methanol alone. The C-butylcalix[4]resorcinarene complex was recrystallized from metha- nol/tert-butanol, and the crystalline complex 8 included both tert- butanol and methanol in a tert-butanol/methanol/C-butylresorcinarene ratio of 5:4:2. Recrystallization of purified C-propylresorcinarene and Scheme 1 *To whom correspondence should be addressed. Telephone: 417-823- 8735. Fax: 417-836-5507. E-mail: ericbosch@missouristate.edu. Web: http:// chemistry.missouristate.edu/31072.htm.