ISSN 0012-5016, Doklady Physical Chemistry, 2012, Vol. 447, Part 1, pp. 210–212. © Pleiades Publishing, Ltd., 2012. Original Russian Text © O.V. Surov, V.V. Vinogradov, N.Zh. Mamardashvili, O.I. Koifman, 2012, published in Doklady Akademii Nauk, 2012, Vol. 447, No. 3, pp. 304–307. 210 The search for materials with unique sorption properties opens up new opportunities for the devel- opment of prospective techniques for gas storage and separation. Traditionally, physical adsorption of gases is studied using materials with great specific surface area and with developed porosity, such as activated carbons, zeolites, and, lately, also carbon nanotubes and porous organometallic structures. However, organic molecular crystals are not usually considered as potential adsorbents because they tend to form close-packed nonporous structures [1]. Simple calix- arene solvates are among the few examples that do not obey this regularity. Desolvation of calixarenes under controlled condi- tions can be used to obtain a crystalline material with active porous phase, which sorbs gases under standard conditions [2, 3]. 4-tert-Butylcalix[4]arene (t-BC) is a universal host compound, which forms clathrates, or inclusion com- pounds, with a variety of guests (solvents) [4, 5]. From most of solvents, t-BC crystallizes to form tetragonal 1 : 1 or 1 : 2 host–guest complexes. Currently, two t-BC polymorphs containing no solvent molecules in the crystal lattice are known: α form obtained upon crys- tallization from tetradecane (its structure consists of close-packed dimers) in which the tert-butyl groups are located in the cavities of the neighboring mole- cules [6]; and β 0 form with a low packing coefficient obtained by sublimation at 280°C under reduced pres- sure [7] in which the t-BC molecules form the bilayer packing motif with a slight shift. Heating of t-BC com- plexes with solvents yields, depending on the desolva- tion conditions, either the more dense self-associated α form or low-density β 0 form [8]. Previously [9], we suggested that long-term heat treatment of the t-BC complex with acetonitrile (t-BC–AN) in vacuum at a temperature below 250°C affords a partly solvated porous structure. This assumption was verified by measuring low-tempera- ture nitrogen adsorption on four t-BC samples, α and β 0 forms, t-BC–AN complex, and partly desolvated sample prepared by long-term heating in vacuum at 220°C. The N 2 adsorption and desorption isotherms on the t-BC samples at 77 K are shown in Fig. 1. For the α and β 0 forms and for the desolvated sam- ple, the N 2 adsorption and desorption isotherms com- pletely coincide (the desorption branches for α and β forms are not shown in Fig. 1), whereas t-BC–AN shows hysteresis over the whole range of relative pres- sures. The isotherms for the α and β 0 forms are type II isotherms according to the Brunauer classification [10], while the isotherm for the partly desolvated sample corresponds to type I, and the isotherm for the t-BC– AN complex has distinctive features of both type I and type II. The specific surface areas of the four t-BC samples determined by the BET method are summa- rized in the table. PHYSICAL CHEMISTRY Microporous Structures Based on 4-tert-Butylcalix[4]arene O. V. Surov a , V. V. Vinogradov a , N. Zh. Mamardashvili a , and Corresponding Member of the RAS O. I. Koifman a, b Received May 28, 2012 DOI: 10.1134/S0012501612110061 a Krestov Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia b Ivanovo State University of Chemical Technology, pr. Engel’sa 7, Ivanovo, 153000 Russia 17.5 0 1.0 P/P 0 v, cm 3 /g (STP) 12.5 7.5 2.5 0.8 0.6 0.4 0.2 4 3 2 1 Fig. 1. Low-temperature nitrogen adsorption and desorp- tion isotherms for t-BC samples: (1) α-form, (2) β 0 -form (the desorption branches are not shown); (3) t-BC–AN complex, (4) desolvated t-BC–AN complex (the adsorbed N 2 volume is decreased fourfold in the plot). Dark symbols correspond to sorption and light symbols, to desorption.