Title
Aggregates of Defined Stereochemical Scaffolds: A Study in Solution of a Zinc(II) Schiff Base Complex Derived from the Enantiopure trans-1,2-Cyclopentanediamine
Author
Ivan Pietro Oliveri, Giuseppe Forte, Giuseppe Consiglio, Salvatore Failla, Santo Di Bella
Year
2017
Journal
Inorganic Chemistry
Abstract
Molecular aggregation of bis(salicylaldiminato) ZnII Schiff base, ZnL, complexes is a topic of current interest. In this paper, we report a novel complex derived from the enantiopure trans-1,2-cyclopentanediamine, (R)-1, in order to probe the effect of the defined stereochemistry on its coordination geometry and aggregation properties, through detailed 1H NMR, DOSY NMR, UV/vis, and circular dichroism spectroscopic studies and accurate DFT calculations. This complex shows several peculiarities in solution, behaving very differently from ZnL complexes and more importantly from the related trans-1,2-diaminocyclohexane derivative. Unexpectedly, experimental data suggest the existence in DMSO of two species in equilibrium, the classical monomeric adduct and a dimer, indicating that the DMSO is not sufficiently strong Lewis basic to completely deaggregate the complex. Also, in chloroform an unusual behavior is observed with the existence of a single defined dimeric species characterized as a dinuclear double helicate Zn2L2 structure which does not deaggregate even with the addition of pyridine in large stoichiometric excess. The formation of mononuclear adducts occurs only when dissolving the complex in the stronger Lewis base pyridine. All these data indicate the helicate (R)-1-h complex has a higher thermodynamic stability than that of the cyclohexane analogue, leading to its unique aggregation properties.
Instrument
J-810
Keywords
Circular dichroism, Inorganic chemistry, Chemical stability, Aggregation