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-diazacyclooctadecane 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 . 3H(2)O, 1 . KSCN . H2O, 2 . NaSCN, 2 . KSCN, 2 . RbSCN and 2 . CsSCN, 3, 3 . LiSCN . H2O, 3 . LiBr . 3H(2)O and 3 . RbSCN. The:compounds 1 . KI . 3H(2)O 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, C-13 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.