Journal of Inclusion Phenomena and Macrocyclic Chemistry 39: 219–228, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 219 Lower Rim Substituted tert-Butylcalix[4]arenes (I). The Structure and Complexing Properties in Ion-Selective PVC Membrane Electrodes ∗ MARIA BOCHE ´ NSKA † , ROBERT BANACH, ANNA ZIELI ´ NSKA and VICTOR CH. KRAVTSOV ‡ Department of Chemistry, Technical University of Gda´ nsk, ul. Narutowicza 11/12, 80-952 Gda´ nsk, Poland E-mail: marboch@ altis.chem.pg.gda.pl (Received: 28 February 2000; in final form: 23 June 2000) Key words: tert-butylcalix[4]arene amides, ion-selective membrane electrodes, selectivity, crystal structure. Abstract Some di- and tetraamide tert-butylcalix[4]arenes were synthesized and described. Their ionophoric properties were studied in liquid membrane ion-selective electrodes. The correlation between the chemical structure (conformation in solution determined by 1 H NMR) and potentiometric ion-selectivity and complex formation constant have been studied. The PVC membrane electrodes based on tetraamides 8–11 show high sodium selectivity, are stable and long lasting. Disubstituted amides 1–7 are selective for larger and more lipophilic ions, as for example guanidinium ion. The crystal structure of the diamide 4 was determined by single crystal X-ray analysis. Crystals of 4 are triclinic, space group P-1, with: a = 16,669(8), b = 17.795(10), c = 20.984(8) Å, α = 91.08(4) ◦ , β = 91.60(3) ◦ , γ = 90.73(4) ◦ and Z = 4. Ionophore 4 posseses a distorted cone conformation and is substituted at the proximal phenol rings. Introduction Tert-butyl calix[4]arenes attracted our attention as prospect- ive ionophores for ion-selective electrodes. They possess rather rigid and lipophilic macrocyclic structures in which four hydroxyl groups are arranged around the central cav- ity and can be modified by introducing different electron donating substituents, for example ester or amide groups [1, 2]. Functionalized calixarenes represent an important class of compounds that can complex both cations and neutral molecules [3]. Unsubstituted tert-butylcalix[4]arenes adopt favorably a cone conformation as a result of stabilization by in- tramolecular hydrogen bond formation between OH groups [4]. In lower rim substituted calix[4]arenes, in the absence of hydrogen bonds, the cone conformation is not always sta- bilized and theoretically all four conformers can be formed: cone, partial cone, 1,2- and 1,3-alternate. The ratio of these conformers depends not only on the substituents but also on the reaction condition and on the polarity of the solvent used in the synthesis [4]. We synthesized several tetra- and disubstituted tert- butyl calix[4]arenes, all being the tertiary amides shown in Scheme 1. Using the same reaction condition, only with morpholide, piperidide, N,N -dibutyl and N,N - methylheptyl amide were tetra substituted products (8–11) ∗ Supplementary data relating to this article have been deposited with the British Library as Supplementary Publication No. 82280 (33 pages). † Author for correspondence. ‡ On leave from the Institute of Applied Physics, Academy of Science, Kishiniev, Republic of Moldova. obtained, however we managed to isolate the respective di- amides 4, 6 and 7 from the reaction mixture. Amides 1, 2 and 3 were obtained as di-substituted calix[4]arenes. The tetrakis-substituted analogs of 1 and 2 are known and were obtained by different synthetic routes [1, 4]. Compounds 1–5 and 7 were obtained in the cone conformation in which both amide groups are in proximal positions. Their conformation was determined on the basis of 1 H NMR spectra. Compound 6 was substituted on the A and C phenol rings. Experimental The synthesis of the compounds Compounds 1–11 were synthesized by the following reac- tion scheme: The chloroamides were prepared as described earlier [5]. The proton NMR spectra were recorded on Varian 200 MHz and 500 MHz spectrometers. The chemical shifts are repor- ted in δ [ppm] using TMS as internal standard. Infrared (IR) spectra were recorded on a Specord 480 (Carl-Zeiss-Jena). Mass spectra were obtained on a AMD-604 Mass Spectro- meter (EI and LSIMS(+) techniques: 70 eV, 8 kV, 5 kHz). The NMR and mass spectra of the compounds confirmed their structure and purity. The organic reagents and solvents used were reagent grade. General procedure for preparation of the bis-(1–7) and tetrakissubstituted calix[4]arenes (8–11) 1 mmole (0.649 g) of p-tert-butylcalix[4]arene was dis- solved in 30 mL of the mixture (5 : 1) of dried tetrahy-