Journal of the Chemical Societ y, Perkin T ransactions 2, 1997, 2249-2256 Structure and ion-complexing properties of an aza-15-crown-5 ether dye: synthesis, crystallography, NMR spectroscopy, spectrophotometry and potentiometry M. V. Alfimov, a A. V. Churakov, b,c Y. V. Fedorov, a O. A. Fedorova, a S. P. Gromov, a R. E. Hester,* ,d J. A. K. Howard, b L. G. Kuz’mina, b,c I. K. Lednev d and J. N. Moore d a N. N. Semenov Institute of Chemical Physics, Department of Photochemistry, Novatorov str., 7a, Moscow, 117421, Russia b Chemistry Department, University of Durham, South Road, Durham, UK DH1 3LE c Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Science, Leninskii prosp. 31, Moscow GSP-1, 117907, Russia d Department of Chemistry, The University of York, Heslington, York, UK YO1 5DD The perchlorate of 2-{2-[4-(13-aza-1,4,7,10-tetroxa-13-cyclopentadecyl)phenyl]ethenyl}-3-ethyl- benzothiazolium (3) has been synthesised and its structure determined in the crystalline state by X-ray diffraction and in solution in acetonitrile by 1 H NMR methods. Complexation with barium and silver cations in solution has been studied in comparison with other model azacrown molecules by spectrophotometric and potentiometric methods. With the exception of the puckered azacrown moiety, the structure of 3 is remarkably planar, consistent with extensive -conjugation throughout the remainder of the molecule in both solid and solution states. Compound 3 forms a stable 1 : 1 complex with Ba 2+ ions in acetonitrile, with a stability constant of K 1 = 80 ± 10 dm 3 mol -1 ; the complexation results in major changes in the electronic absorption spectrum of 3, consistent with binding to the azacrown moiety. A model compound, phenylaza-15-crown-5 (2a), was found to bind Ba 2+ to form both a 1 : 1 ligand–metal complex (LM), with a stability constant of K 1 = (2.0 ± 0.2) × 10 4 dm 3 mol -1 , and a 2 : 1 (L 2 M) complex, with a stability constant of K 2 = 220 ± 20 dm 3 mol -1 for binding of the second ligand. The electronic absorption and NMR spectra both indicate binding of the ‘hard’ Ba 2+ cation to the azacrown oxygen atoms. However, by contrast, the evidence from NMR data shows that the ‘soft’ Ag + cation complexes with 2a mainly through a strong interaction with the azacrown nitrogen atom, giving a 1 : 1 complex with a stability constant of K 1 = 6 ± 1 dm 3 mol -1 , determined by potentiometry. No complexation of 3 with Ag + is observed. Studies of the simple aza-15-crown-5 ether reveal strong complexation with both Ba 2+ (K 1 × K 2 > 10 12 dm 6 mol -2 ) and Ag + [K 1 = (1.15 ± 0.10) × 10 4 dm 3 mol -1 and K 2 = 450 ± 20 dm 3 mol -1 ]. Introduction Chromo- and fluoro-ionophores that combine an organic dye and an ionophore moiety within a single molecule provide a basis for the development of supramolecular ionic devices. 1–6 Absorption and luminescence spectroscopies are commonly used to study the affinity of such compounds for metal cations, 7–13 but these techniques provide relatively little inform- ation on the structural characteristics which are important for improved molecular design. The additional study of crystals by X-ray diffraction (XRD) 14 and of solutions by vibrational spec- troscopy has been shown to provide usefully detailed inform- ation on such systems. 15–19 1 H NMR spectroscopy also has been used to investigate complex formation between a styrylbenzo- thiazolium 15-crown-5 ether† dye and alkali and alkaline-earth metal cations. 20 We report here the synthesis and extensive study of a styryl- benzothiazolium dye containing a phenylmonoaza-15-crown-5 ether† group, using a simple phenylaza-15-crown-5 ether for comparison. The molecular structure of the ionophores in cation-free and cation-complexed forms have been investigated in crystals by XRD and in solution by 1 H NMR spectroscopy, including COSY and NOESY measurements. The complex- ation of these ionophores with ‘hard’ (Ba 2+ ) and ‘soft’ (Ag + ) † Recommended IUPAC name for aza-15-crown-5 ether is 13-aza- 1,4,7,10-tetroxacyclopentadecane. metal cations in acetonitrile has been studied also by UV–VIS absorption spectrophotometry and by potentiometry. Results and discussion Synthesis The synthesis of the styrylbenzothiazolium dye 3, containing the N-phenylaza-15-crown-5 group, is summarized in Scheme 1. 3-Ethyl-2-methylbenzothiazolium iodide, 1a, was used for the preparation of the perchlorate, 1b. The formyl derivative of phenylaza-15-crown-5, 2b, was prepared according to the liter- ature, 21 and the condensation of 1b with 2b was carried out in absolute ethanol in the presence of pyridine as a catalyst. Crystallography Several aspects of the structure within the crystals of dye 3, which contain equal numbers of positively charged organic molecules and perchlorate ions, are shown in Figs. 1–3. Fig. 1(a) and (b) show the general conformational arrangement of the organic cation; its near-planarity, apart from the crown moiety, is particularly striking. Four almost rigorously planar sub-units may be dis- tinguished within 3: the benzothiazolium system (plane 1), the conjugated bonds C(11)C(12)C(13)C(14) (plane 2), the phenyl ring C(14)  C(19) (plane 3), and the amino moiety C(1)C(10)C(17)N(1) (plane 4). The dihedral angles between the planes 1/2, 2/3 and 3/4 are 5.4, 6.7 and 6.5°, respectively. With Центр Фотохимии Российской Академии Наук Сборник публикаций 1997 65