Auxiliary ligand-directed synthesis of cadmium(ii) and zinc(ii) complexes from 1-D chains to 3-D architectures with 5-nitroisophthalate

Abstract

A series of cadmium(II) and zinc(II) metal–organic frameworks, [Cd(NIPH)(2-apy)(H₂O)·(H₂O)] (1), [Cd(NIPH)(4-apy)₂(H₂O)] (2), [Zn₂(NIPH)₂(μ₃-OH)(H₂O)·(2-Hapy)] (3), [Zn₅(NIPH)₄(μ₃-OH)₂(μ₂-OH)(H₂O)·(3-Hapy)] (4), and [Zn₅(NIPH)₄(μ₃-OH)₂(μ₂-OH)(H₂O)·(4-Hapy)·(H₂O)] (5), were synthesized by hydrothermal reactions of the corresponding Cd(II) and Zn(II) salts with 5-nitroisophthalic acid (H₂NIPH) in the presence of aminopyridine (apy) auxiliary ligands. These frameworks exhibit three typical structural features: 1 and 2 possess a 1-D double-stranded loop-like chain and a 1-D linear chain formed by [Cd₂N₂O₁₀] dinuclear building blocks and [CdN₂O₅] monoclear building blocks, respectively; 3 is a 2-D anionic framework consisting of [Zn₄O₁₆] tetranuclear building blocks; both 4 and 5 are 3-D anionic frameworks constructed by both [Zn₄O₁₆] tetranuclear and [Zn₆O₂₂] hexanuclear building blocks. The apy ligands participate in constructing frameworks of 1 and 2, but are protonated in the channels of 3–5 as charge-balancing and space-filing agents. The thermal stability, luminescent properties and ion-exchange behavior of the complexes were investigated.