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

Abstract

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

Deaggregation properties and transmetalation studies of a zinc(ii) salen-type Schiff-base complex

“…[24][25][26][27][28][29] Among Zn(salen)-type complexes, colourful derivatives from the 2,3-diaminomaleonitrile, Zn(salmal), are certainly those more interesting for their optical absorption and fluorescence emission properties upon deaggregation. [30][31][32][33][34][35][36][37] In order to further explore these varied characteristics, we have chosen a Zn(salmal) complex, 1, having different substituents on the salicylidene rings. In particular, we found that the presence of 5-tert-butyl-bulky substituents makes this complex sufficiently soluble in a range of coordinating/non-coordinating solvents, giving us the possibility to explore its spectroscopic properties in solution, even in comparison to previous studies on amphiphilic Zn(salmal) complexes with longer alkyl substituents.…”

A simple approach based on transmetalation for the selective and sensitive colorimetric/fluorometric detection of copper(ii) ions in drinking water

“…[44][45][46] In particular, derivatives from the 2,3-diaminomaleonitrile, Zn(salmal), are characterized by relevant optical spectroscopic changes in relation of the nature of the aggregate species or monomeric adducts. [47][48][49][50][51][52][53] We have demonstrated that in solution of weak coordinating solvents a 5-tert-butyl substituted Zn(salmal) complex (1) forms relatively stable adducts which easily transmetalate with divalent ions of the first transition series, but with a different rate. 54 In particular, the transmetalation with Cu 2+ ions is faster than that with other cations, regardless of the nature of the counteranion.…”

A Zinc(II) Schiff Base Complex as Fluorescent Chemosensor for the Selective and Sensitive Detection of Copper(II) in Aqueous Solution

“…Zn(salen)-type complexes are characterized by varied photophysical properties strongly related to the structure of the diimine bridge [21,22], substituents on the salicylidene rings, and non-coordinating or coordinating nature of the solvent [23][24][25]. Among them, colorful complexes derived from 2,3-diaminomaleonitrile, Zn(salmal), are the most interesting also for their fluorescent properties [26][27][28][29][30][31][32][33][34][35].…”