Supramolecular Aggregation of a New Substituted Bis(salicylaldiminato)zinc(II) Schiff-Base Complex Derived from trans-1,2-Diaminocyclohexane

Giuseppe Consiglio,Salvatore Failla,Ivan Oliveri

doi:10.3390/inorganics6010008

Abstract

In this contribution is reported the synthesis, characterization, and aggregation properties in solution of a novel Zn(II) complex, (R)-2, derived from the enantiopure chiral trans-1,2-diaminocyclohexane and a substituted salicylaldehyde. Detailed 1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies and chemical evidence allowed to investigate the nature of aggregate species in solution. The high solubility of (R)-2 in solution of the non-coordinating chloroform solvent leads to formation of various aggregates, some of them consisting of large oligomers estimated to contain up to 27 monomeric units. The chiral trans-stereochemistry of the bridging diamine favors a different aggregation mode in these complexes, both in the oligomers and dimers, involving a tetrahedral coordination geometry around the metal center. Overall data suggest the formation of helical oligomers, (ZnL)n, in freshly prepared chloroform solutions which, by standing or heating, evolve towards a more thermodynamically stable, dinuclear double-helicate Zn2L2 dimer.

Highlights

Molecular aggregation is a topic of current interest involving various properties and applications [1,2,3,4]
In recent years we have been involved in the study of the aggregation properties of bis(salicylaldiminato)zinc(II) Schiff-base complexes, derivatives from substituted salicylaldehydes and 1,2-diamines [5,6,7,8,9,10,11]
The switching from pentacoordinated monomeric adducts in coordinating solvents to dimeric aggregates in chloroform solutions has monomeric adducts in coordinating solvents to dimeric aggregates in chloroform solutions has always always accompanied by an up-field shift of these signals, because of the involved hydrogens lie under accompanied by an up-field shift of these signals, because of the involved hydrogens lie under the shielding zone of the π electrons of a conjugated system [7,8,9,10,11]

Summary

Introduction

Molecular aggregation is a topic of current interest involving various properties and applications [1,2,3,4]. A variety of supramolecular architectures [13,14,15,16,17,18], mesomorphic [19,20,21,22], and self-assembled nanostructures [23,24,25,26,27] have been found, mostly because of intermolecular Zn···O axial interactions involving pentacoordinated square-pyramidal Zn(II) geometries These species exhibit interesting photophysical properties [28,29,30,31] and are sensors of various Lewis bases [32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53]. While in the case of the cis-1,2-diaminocyclohexane derivative an asymmetric dimeric aggregate with a typical Zn(II)

Methods

Results

Discussion

Conclusion