Aggregation properties of bis(salicylaldiminato)zinc(ii) Schiff-base complexes and their Lewis acidic character?

Dalton Transactions Pub Date: 2011-10-18 DOI: 10.1039/C1DT11295C

Abstract

The synthesis, characterization, 1H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported. Detailed 1H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. Chloroform solutions of complexes where the bridging diamine contains a naphthalene or the pyridine nucleus are always characterized by the presence of defined dimer aggregates, whereas oligomeric aggregates are likely formed by complexes where the bridging diamine contains a benzene ring. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the ZnII ion, accompanied by considerable changes in the 1H NMR and optical absorption spectra. The effect of the alkyl chains length seems to play a minor role in the aggregation properties, as noticed by 1H NMR data, optical absorption and fluorescence spectra, which remain almost unaltered on changing the chain length.

Graphical abstract: Aggregation properties of bis(salicylaldiminato)zinc(ii) Schiff-base complexes and their Lewis acidic character
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