Structures of LiSCN, NaSCN, KSCN, RbSCN, and CsSCN complexes with 3 ',5 '-difluoro-4 '-hydroxybenzyl-armed monoaza-15-crown-5 ether (5) were investigated. The Li+ and Na+ complexes are (1:1)(n) polymer-like complexes bridged by hydrogen bonding. On the other hand, the K+, Rb+, and Cs+ complexes are polymer-like complexes bridged by the fluorine atoms of the side arms. The titration calorimetry and F-19 NMR titration experiments suggest that one or both fluorine atoms along with the oxygen atom of the phenolic OH group coordinate to the alkali metal ions incorporated in the crown part of a second armed ligand to give polymer-like complexes in solution. The FAB-MS data indicated that larger alkali metal ions form more stable polymer-like complexes.