1570 C 16 H 20Fe202S2 +. C10~- KENNARD, O., WATSON, D. G., ALLEN, F. H., MOTHERWELL,W. D. S., TOWN, W. G. & RODGERS, J. (1975). Chem. Br. II, 213-216. MITCHELL, J. & BOEYENS, J. C. A. (1970). Acta Cryst. B26, 1121-1124. ROBERTSON,A. (1948). Nature (London), 162, 153. SHELDRICK, G. M. (1976). SHELX76. Program for crystal structure determination. Univ. of Cambridge, England. STROHMEIER, W., VON HOBE, D., SCHONAUER,G. & LAPORTE, H. (1962). Z. Naturforsch. 176, 502-504. TRINH-TOAN, TEO, B.-K., FERGUSON,J. A., MEYER,T. J. & DAHL, L. F. (1977). J. Am. Chem. Soc. 99, 408-416. Acta Cryst. (1984). C40, 1570-1572 2,5,8,11,14,17,20-Heptaoxahenicosane-Barium Isothiocyanate, C14H30OT.Ba(NCS)* BY GABRIELA WEBER, FUMITOSHI HIRAYAMA AND WOLFRAM SAENGER Institut ffir Kristallographie der Freien Universitfit, Takustrasse 6, D-1000 Berlin 33, Federal Republic of Germany AND GEORGE M. SHELDRICK lnstitut ffir Anorganische Chemie der Universitfit, Tammannstrasse 4, D-3400 Gd'ttingen, Federal Republic of Germany (Received 9 March 1984; accepted 30 May 1984) Abstract. M r= 563.89, triclinic, P1, a = 7.859 (3), b=ll.010(4), c=14.299(4)A, a=89.65(2), fl= 78.39 (3), 7= 78.50 (3) °, V= 1186.9 (7) A 3, Z = 2, D x = 1.578 (1) Mg m -a, 2(Mo Kc0 = 0.71069 A, ~ = 1.87 mm -1, F(000) = 568, T= 291 K, final R = 0.025 for 3979 observed reflections. The open-chain oligoether approximates to one turn of a helix, thus facilitating a sevenfold coordination of the cation to all the ether O atoms (mean 2.91 A) and additional interactions with the two anions (mean Ba2÷...N - distance = 2.83 A). No linkages between the complex units were observed. Introduction. Linear oligoethers containing (--CH 2- CH2--O--)n units are well established ligands for alkali and alkaline-earth metal ions (V6gtle & Weber, 1979; Hilgenfeld & Saenger, 1982). Terminal donor groups such as aromatic bases (e.g. V6gtle & Sieger, 1977; Saenger, Suh & Weber, 1979), -OH or -COEH (capable of additional hydrogen bonding) (e.g. Hughes & Wingfield, 1978; Hughes, Mortimer & Truter, 1978; Yamaguchi, Miki, Yasuoka & Kasai, 1982) or, at least, terminal aromatic nuclei (e.g. Sieger & V6gtle, 1978; Hilgenfeld et al., 1984) seemed essential for the stability of the complexes formed (e.g. Tiimmler, Maass, V6gtle, Sieger, Heimann & Weber, 1979; Parsons, Truter & Wingfield, 1981). Complexes with unsubstituted oligoglymes could be obtained (Sieger & V6gtle, 1978) but X-ray investigations have been reported only for complexes with mercuric salts (Iwamoto, 1973), CdCI 2 *Structures of Polyether Complexes. XXI. Part XX: Suh, Namgung, Ku Yoon, Saenger & V6gfle (1984). (Iwamoto & Wakano, 1976) and for a compound in which potassium accepts additional n-interactions (Hodgson & Raymond, 1972). We report here the first structure determination of a complex between an alkaline-earth metal cation and an unsubstituted oligoglyme. Experimental. Sample kindly provided by Professor F. V6gtle, University of D-5300 Bonn (FRG), crystal ca 0.7 x 0.3 x 0.1 mm, grown from ethyl acetate/ petroleum ether; Stoe-Siemens four-circle diffrac- tometer, cell dimensions from 20 angles for 24 reflections (20 _< 20 <_ 25°); 5261 profile-fitted (Clegg, 1981) data up to 20= 50 °, -9 < h < 1, -13 < k < -13, -17 _< l _< 17; no significant decline in intensities of three standard reflections; empirical absorption correction based on ~, scans, max./min. transmission 0.63/0.53; 4169 reflections unique (Rl, t =0.012), 3982 with F> 3a(F), three suppressed (machine fault); Ba 2+ position from an E x F Patterson map, positions of remaining non-H atoms from a subsequent difference Fourier synthesis; structure refined anisotropically by blocked-cascade least squares on F, C(3)-C(4) restrained to 1.4800 _+0-0003 A because of slight conformational (irresolvable) disorder; H atoms included in idealized positions [C-H= 0.96A; U(Hi)= 1.2Ueq(Ct)], methylene H atoms treated as 'riding atoms', methyl groups as 'rigid groups'; 259 LS parameters, R = 0.025, wR --0.027, w-l= tr2(F) + 0.0004F 2, S = 1.25, slope of normal probability plot 1.15, max. A/a=0.06 [rotation of methyl group C(1)], mean 0.004, largest peak 0.66 e A -3 (close to Ba2+), largest hole 0.35 e A -3 in 0108-2701/84/091570-03501.50 © 1984 International Union of Crystallography