Hydrogen Bond, π–π, and CH–π Interactions Governing the Supramolecular Assembly of Some Hydrazone Ligands and Their Mn^II Complexes – Structural and Theoretical Interpretation

Abstract

Abstract The hydrazone Schiff base ligands ( E )‐ N′ ‐(2‐hydroxybenzylidene)acetohydrazide (H L 1 ) and ( E )‐ N′ ‐(2,3‐dihydroxybenzylidene)acetohydrazide (H 2 L 2 ) with a functional group variation in the aromatic moiety have been synthesized. The ligands have been used to synthesize the following Mn II complexes: the mononuclear complex [Mn(H L 1 ) 2 ][ClO 4 ] 2 · 2H 2 O ( 1 ), the cocrystallized discrete dinuclear complex {[Mn(H L 1 ) 2 ] · [Mn( L 1 ) 2 ]}[ClO 4 ] 2 ( 2 ), and the phenoxido‐bridged dinuclear complex [Mn(μ‐H L 2 )(H 2 O)] 2 [ClO 4 ] 2 ( 3 ). The ligands and the complexes were characterized by FTIR and UV/Vis spectroscopic techniques, and their crystal structures were determined by single‐crystal X‐ray diffraction analysis. 1 H and 13 C NMR spectroscopy shows evidence of keto–enol tautomerism of the ligands in solution. All of the compounds develop hydrogen‐bonded assemblies of different dimensionalities and architectures. CH–π and π–π interactions also contribute significantly to the overall binding energies of the supramolecular assemblies. The supramolecular interaction energies have been computed at the BP86‐D3/def2‐TZVPD level of theory.