Anion tuning of Zn2+ architectures using a Tris-base salicylic ligand

Abstract

In this study, a hydroxyl-rich Schiff base ligand, H₄L, and its resulting complexes with ZnCl₂, Zn(CH₃COO)₂ and Zn(ClO₄)₂ were explored. Interestingly, depending on the zinc salt and/or the crystallisation method, four unique structures were obtained. A synthesis with ZnCl₂ gave 1, a mononuclear structure ((H₃L)₂Zn), while with Zn(CH₃COO)₂, a trinuclear system [(H₃L)₂Zn₃(CH₃COO)₄], 2, was found. Interestingly two multinuclear architectures were observed with Zn(ClO₄)₂. Firstly, diethyl ether diffusion of a methanolic reaction mixture with minimal atmospheric air volume gave 3, a hexanuclear architecture of the type [(H₂L)₄(H₃L)₂Zn₆](ClO₄)₂, while slow evaporation of a similar mixture gave 4, a nonanuclear architecture with the formula [(H₂L)₆Zn₉(CO₃)₂](ClO₄)₂. Compound 4 unexpectedly fixed atmospheric CO₂ as CO₃²⁻, incorporating it into the architecture. As expected, a diethyl ether diffusion with a larger volume of air (∼100 mL) of a similar methanolic reaction mixture gave a mixture of 3 and 4. In addition, bulk samples of all compounds were also investigated by PXRD, and results are in good agreement with the observed single crystal data. Furthermore, complexes 1–4 were characterised using FT-IR and simultaneous thermal analysis (STA), and additionally the photophysical properties of H₄L and complexes 1–4 have also been explored.