Structure and aggregation properties of a Schiff-base zinc(II) complex derived from cis-1,2-diaminocyclohexane

This contribution explores the effect of the bridging diamine upon the aggregation properties of a ZnIISchiff-base complex, 1, both in the solid state and in solution. The X-ray structure of 1, resulting from theharvest of good quality crystals using chloroform and diethyl ether as solvents, shows the presence of adensely packed dimer in the solid state which pentacoordinates two Zn atoms involved in a μ-phenoxobridge. Detailed studies in solution, through 1H NMR, DOSY NMR, and optical spectroscopic investigations, indicate the typical aggregation/deaggregation behaviour on switching from non-coordinating tocoordinating solvents, in relation to the Lewis acidic character of such ZnII complexes. Thus, while inDMSO-d6 both 1H NMR and DOSY studies suggest the existence of monomeric species, in chloroformsolution experimental data support the existence of aggregates. However, unlike our previous studies, 1HNMR data in chloroform solution indicate the existence of an asymmetric dimer, as observed in the X-raycrystal structure. This further evidences a very rigid backbone of the dimeric aggregate and can be relatedto the defined stereochemistry of the chelate cis-1,2-diaminocyclohexane bridge.