Unexpected Structure of a Helical N4‐Schiff‐Base Zn(II) Complex and Its Demetallation: Experimental and Theoretical Studies

A new Zn‐N4‐Schiff base L=((±)‐trans‐N,N’‐Bis(2‐aminobenzylidene)‐1,2‐diaminocyclohexane) complex was synthesized and fully characterized, showing an unexpected self‐assembled double‐stranded helicate structure. The X‐ray crystal analysis of the Zn2L2 complex ((C40H44N8Zn2,CH2Cl2, a=14.2375(3) A, b=16.7976(4) A, c=16.1613(4) A, monoclinic, P21/n, Z=4) shows a centrosymmetrical structure in which zinc atoms are in distorted tetrahedral environments, revealing an M‐ (R, R) left‐handed helicity in its asymmetric unit. However, it was observed that this dinuclear complex is thermodynamically unstable in the presence of small water amounts and undergoes demetallation into free N4‐Schiff base ligand and ZnO nanoparticles. This hydrolysis process was thoroughly identified and monitored through detailed 1H NMR, DOSY NMR analysis. The reaction mechanism of this demetallation event was elucidated by using the DFT method, involving an activation energy smaller than 13 kcal/mol. Besides, a theoretical mechanism of the demetallation process is given for the first time.