Metal complex formation of bisform-8-quinolinols linked with 5- and 5'-positions

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In this work, bisform-8-quinolinols linked at the 5- and 5'-positions by spacer groups having different chain length have been prepared with reactions of 5-chloromethyl-8-quinolinol and 1, n-alkanediols. Both UV-vis absorption spectra (including the pH dependences) and NMR spectra of the bisforms suggest absence of the interaction between the two quinolinol rings. Nevertheless, metal complex formations of the bisforms with Al3+, Pd2+, and Ln3+ are enhanced by the chelate effects as compared with those of 8-quinolinol. The bisforms also act as bridge-ligands to form polynuclear complexes or ring-like 2:2 complex with Pd2+. In the ring-like complex, the absorption spectra clearly indicate the presence of pai-pai interactions between the two quinolinol rings in the bisforms. The bisfrom-8-quinolinols can be expected as new types of chelate reagents based on 8-quinolinol derivatives.