Supramolecular Aggregates of Defined Stereochemical Scaffolds: Aggregation/Deaggregation in Schiff-Base Zinc(II) Complexes Derived from Enantiopure trans-1,2-Diaminocyclohexane.
This contribution explores, through detailed1H NMR, DOSY NMR, optical absorption, and circular dichroism spectroscopic studies, the aggregation properties in solution of noncoordinating solvents of some new ZnIISchiff-base complexes, (R)-1, (S)-1, and (R)-2, derived from the chiral trans-1,2-diaminocyclohexane. It is found that chloroform solutions of 1 are characterized by the presence of three species, the predominance of which consists of large oligomeric aggregates. For chloroform solutions of 1, upon heating or standing, all species are irreversibly converted into a dimer, 1C, which is very stable and hardly disaggregable. Analysis of1H NMR, UV/vis, and CD spectroscopic data and chemical evidence allow proposing a double helicate Zn2L2structure with a tetrahedral coordination around the ZnIIions for 1C, as a consequence of the defined stereochemistry of the trans-1,2-diaminocyclohexane chelate bridge. This represents a different, uncommon aggregation mode in ZnIIcomplexes of tetradentate Schiff-bases.
Dipartimento di Scienze Chimiche, Università di Catania , I-95125 Catania, Italy.
Giuseppe
G
Consiglio
Dipartimento di Scienze Chimiche, Università di Catania , I-95125 Catania, Italy.
Ivan Pietro
IP
Oliveri
Dipartimento di Scienze Chimiche, Università di Catania , I-95125 Catania, Italy.
Salvatore
S
Failla
Dipartimento di Scienze Chimiche, Università di Catania , I-95125 Catania, Italy.
Santo
S
Di Bella