Effect of anions on the self-assembly of Zn(ii) with a hydrogenated Schiff baseligand: structural diversity and photoluminescent properties

Abstract

A flexible tetradentate ligand, 1,2-bis(4′-pyridylmethylamino)ethane (L), has been used for assembly with different Zn(II) salts. Six complexes with diverse structures from zero- to two-dimensional array have been prepared under mild conditions. Complexes (Zn₂LCl₄·2H₂O)₂ (1) and (Zn₂LBr₄·H₂O)₂ (2) form novel discrete M₄L₂ square metallacycles, which are further linked by Cl (or Br)⋯H hydrogen bonds and weak intermolecular interactions to result in 3D frameworks. Complex [ZnL(SCN)₂·2H₂O]_n (3) is a one-dimensional hinged chain. Different chains are stacked in a staggered pattern by the π–π interactions. Complex (ZnLCl₂·2H₂O)_n (4) displays an infinite one-dimensional hinged chain too, but its 3D supramolecular structure is formed by the intrachain and interchain hydrogen bonds. Both complexes [ZnL(H₂O)₂·2ClO₄·4H₂O]_n (5) and [ZnLAc(H₂O)·Ac·2H₂O]_n (6) exhibit 2D networks. Structural analyses of complexes 1–6 suggest that anions Cl⁻, Br⁻, SCN⁻, ClO₄⁻, and Ac⁻ play an important role in the formation of those complexes with hydrogenated Schiff base L. Furthermore, the photoluminescence of complexes 1–6 have also been investigated in the solid state.