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

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.