Self‐Assembly, Structure and Solution Dynamics of Tetranuclear Zn2+ Hydrazone [2×2] Grid‐Type Complexes

Abstract

AbstractWe describe the self‐assembly processes as well as the structural and physico‐chemical properties of [2×2]Zn2+4 grid complexes involving the bis‐tridentate ligands 7–12, based on bis(hydrazone)pyrimidine complexation subunits and octahedrally coordinated Zn2+ ions. The NMR spectroscopic data and the X‐ray crystal structure results indicate that in solution and in the solid state the complexes 13–18 adopt a very compact arrangement providing stable [2×2] hydrazone‐grid arrays. The π–π stacking between the phenyl ring and the hydrazone units of the perpendicular ligands in the complexes induces a perfect orthogonal arrangement suitable for applications in self‐organized metallosupramolecular systems. Zinc complexes provide an opportunity to study the acid–base chemistry without the added effects due to paramagnetism or redox chemistry. The intermediate protonated grids undergo relatively rapid proton exchange on the NMR timescale, the presence of a sharp pyrimidine proton resonance suggesting that there is significant delocalization of the negative charge along the backbone of the ligand. Rotation of the phenyl ring is observed. It involves probably a mechanism in which one of the ligands partially dissociates allowing the initially intercalated phenyl group to rotate, before recoordination of the terminal pyridine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)