Molecular structure of novel polymer-like complexes of armed-azacrown ethers with alkali-metal cations

Abstract

Armed-azacrown ethers N,N′-bis(4-hydroxy-3,5-dimethylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacylooctadecane 1, N-(4-hydroxy-3,5-dimethylbenzyl)-1,4,7,10-tetraoxa-13-azacyclopentadecane 2 and -1,4,7-trioxa-10-azacyclododecane 3, and their alkali-metal complexes were prepared. Single crystal structures have been determined for 1, 1·KI·3H₂O, 1·KSCN·H₂O, 2·NaSCN, 2·KSCN, 2·RbSCN and 2·CsSCN, 3, 3·LiSCN·H₂O, 3·LiBr·3H₂O and 3·RbSCN. The compounds 1·KI·3H₂O and 1·KSCN·H₂O are normal 1:1 complexes, but 2·NaSCN, 2·KSCN, 2·RbSCN and 2·CsSCN are novel polymer-like (1:1)n complexes in which the phenolic OH group in the side arm of the crown ether co-ordinates to the cation incorporated in the crown moiety of another molecule. In the complexes of 3, when Li⁺ is used as guest cation, the normal 1:1 complex is obtained, but Rb⁺ forms a polymer-like (2:2)n complex. Fourier-transform IR spectra showed that the O–H stretching band of the phenolic OH group in the polymer-like complexes shifted to lower frequency by ca. 210–290 cm^–1 compared with those of the corresponding host compounds. Also, ¹³C NMR titration experiments indicated that the stoichiometry of the alkali-metal complexes with 2 and 3 in CD₃CN–CD₃OD (5:1) solution is 1:1, and thus they do not form polymer-like complexes under these conditions.