Bisform-8-quinolinols linked at the 2- and 2'-positions by using three kinds of spacer groups have been synthesized according to the Knoevenagel reaction. The acid-dissociation constants (p
Ka1) of the ligands and their formation constants (log
kf) with several metal ions were measured in 50% v/v aqueous dioxane by UV-vis spectroscopy. In the case of the ligand having an ethane spacer group, two p
Ka1 values were observed, which suggests that it may adopt a gauche conformation in acidic solutions, and can form 1 : 1 intramolecular complexes with Cu
2+ or Zn
2+. The log
kf of Cu
2+, Zn
2+,Ga
3+ and In
3+ are found to be higher than the corresponding values for 8-quinolinol. In these metal ions, Ga
3+ forms the most stable complex at the lower pH values, and the molecular structure roughly determined by X-ray analysis is considered to be 2 : 2 Ga-bisquinolinol chelates bridged by a twisted Ga-O-Ga. In addition, the Ga
3+ complexes exhibited advantageous emission intensity over the Zn
2+ complex. The bisform-8-quinolinols adopting a gauche comformation act as a tetradentate ligand and strongly coordinate with some metal cations.
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