Manganese(II) and zinc(II) coordination polymers based on 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid: synthesis, structure and properties

Abstract

Two metal–organic frameworks based on a multifunctional ligand 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid (H₃L), [Mn(HL)(C₂H₅OH)]_n (1) and {[Zn(HL)(H₂O)₂]·H₂O}_n (2), have been hydro/solvothermally synthesized and characterized by IR, elemental analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses. In 1, (HL)^2– ligands adopt the μ ₃-kN,O:kN′,O′:kN′′ coordination mode and use their imidazoledicarboxylates to bis-chelate Mn^II into left- and right-handed helixes which are further bridged into a mesolayer structure with (4·8²) topology through the coordination of their pyridyl groups. In 2, (HL)^2– ligands only use their imidazoledicarboxylates to bis-chelate Zn^II into linear chains which are further linked into a 2D supramolecular framework through interchain hydrogen–bonding interactions. Interestingly, the structures of 1 and 2 are mainly dominated by the bis-N,O-chelation of the imidazoledicarboxylate in (HL)^2–. As for the formation of the imidazoledicarboxylate-bridged helical chains in 1 or straight chains in 2, it largely depends on the cis- or trans-chelation of two imidazoledicarboxylates around the same metal center. Magnetostructural analysis of 1 discloses that the bis-N,O-chelating imidazoledicarboxylate of (HL)^2– transmits antiferromagnetic interactions along the imidazoledicarboxylate-bridged helical chain with the spin-coupling constant of –0.71 cm^–1. Additionally, 2 emits greatly enhanced blue fluorescence mainly originating from the intraligand charge transition.

Keywords:

• Crystal structure
• fluorescence
• 4,5-imidazoledicarboxylic acid derivative
• magnetism
• metal–organic frameworks

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (Grant Number 21271157) and the Foundation and Research in Cutting-edge Technologies in the Project of Henan Province (Grant Number 122300410092).