Co-ordination chemistry of macrocyclic polyethers. An unusual conformation of complexed 18-crown-6; X-ray crystal and molecular structure of a 1:2 host–guest complex of 18-crown-6 with benzenesulphonamide

Abstract

In the 1 : 2 host-guest complex formed between 1,4,7,10,13,16-hexaoxacyclo-octadecane (18-crown-6) and benzenesulphonamide, the crown ether adopts nearly the same conformation as the uncomplexed hexaether ; the complex is held together mainly by N-H ---0 hydrogen bonds.THE ability of crown ethers to form host-guest complexes with alkaline earth metal cations and ammonium salts is well known. Preliminary X-ray crystallographic results of Dunitz et aZ.3 shows that 18-crown-6 exists in different W . Germany) conformations in free and complexed forms. X-Ray crystal structure determinations of complexes of crown ethers with CH-4 and OH-acid5 substrates show that the crown ether in these compounds adopts a conformation with D,,-symmetry which is typical of potassium complexes.We report the solid-state structure of the product of reaction of 18-crown-6 with the NH-acid substrate, benzenesulphonamide, which can be obtained by a method similar to that used earlier for other compounds.6 Crystals of the complex are obtained as colourless needles, m.p. 365 K, which gave satisfactory microanalytical data.

A 2:1 complex of 2,4-dinitroaniline and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)

“…18-Crown-6 normally adopts a conformation of approximate D3a symmetry both in cationic complexes (e.g. Dunitz, Dobler, Seller & Phizackerley, 1974;Nagano, 1979) and when hydrogen bonding to guest species (Nagano, Kobayashi & Sasaki, 1978;Goldberg, 1975;Kaufmann et al, 1977;Hilgenfeld & Saenger, 1981) including cationcoordinated water (Kn6chel, Kopf, Oehler & Rudolph, 1978b). With dihydrated uranyl nitrate (Bombieri, de Paoli & Immirzi, 1978) or benzenesulphonamide (Kn6chel et al, 1978a), however, this symmetry with exclusively anti-gauche-anti units of alternating signs is broken in favour of an elongated conformation g+g+aag-aag-ag-g-aag+aag+a which is related to that of the uncomplexed ether (Maverick, Seller, Schweizer & Dunitz, 1980).…”

The polarographic determination of stability constants of urea/crown ether complexes in methanol

“…The least-squares approach is aimed at minimizing U, the sum of the residuals u = f w,(Fo,, -J',ed2, 1 (6) where N denotes the number of data points and w, is the weighting factor (which is set to one in the POLAG program); Fobs is obtained from the experimentally found parameters using Eqn. 4 and Fcalc is calculated from Eqn.…”

Transition-metal–crown-ether complexes. III. Seven-coordinate CoII in dinitratocobalt(II)–12-crown-4 and diaquacobalt(II) dinitrate–15-crown-5

“…are then hydrogen bonded to the crown ether: Mn(NO3)2.6H20.18-crown-6 (Kn6chel, Kopf, Oehler & Rudolph, 1978), [Mn(H20)6](C104)2.18-crown-6 (Vance, Holt, Varie & Holt, 1980), and [Co(H20)6]- [COC14]. 18-crown-6.…”