Binding Properties of a Dinuclear Zinc(II) Salen-Type Molecular Tweezer with a Flexible Spacer in the Formation of Lewis Acid-Base Adducts with Diamines

In this paper we report the binding properties, by combined 1H NMR, optical absorption, and fluorescence studies, of a molecular tweezer composed two Zn(salen)-type Schiff-base units connected flexible spacer, towards series ditopic diamines having strong Lewis basicity, with different chain length rigidity. Except for 1,2-diaminoethane, in all other cases formation stable 1:1 acid-base adducts large constants is demonstrated. For α,ω-aliphatic diamines, progressively increase increasing alkyl chain, thanks to nature spacer parallel decreased conformational strain upon binding. Stable are also found even short rigid structures. Given their preorganized structure, these latter species not subjected loss degrees freedom. The characteristics have been exploited colorimetric fluorometric selective sensitive detection piperazine.