Ligand concentration-dependent supramolecular complexes with uncoordinated carbonyl groups based on a new pyrazole carboxylic acid ligand

Abstract

One new pyrazole-based ligand, 1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic acid (H₂cmdpca), has been synthesized and characterized. Structural analysis reveals that H₂cmdpca crystallizes in the monoclinic system and adopts a 3-D supramolecular network via the interaction of intermolecular hydrogen bonds. The reactions of Cd(II) ions with H₂cmdpca and 4,4′-bipyridine (4,4′-bpy) afforded three metal complexes, [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)₃]·H₂O (1), [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)]·3H₂O (2), and [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)] (3). Structural analyses reveal that these complexes are all monoclinic and 1, 2, and 3 exhibit mononuclear, 1-D chain, and 1-D with binuclear loop structures, respectively, which are further assembled into 3-D supramolecular frameworks through non-covalent interactions. 1 and 2 are true supramolecular isomers, while 2 and 3 are “pseudo-supramolecular” isomers. In addition, the thermal stability and luminescent properties of the complexes are also investigated.

One new ligand, (H₂cmdpca), and three supramolecular complexes, [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)₃]·H₂O (1), [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)]·3H₂O (2), and [Cd(4,4′-bpy)(Hcmdpca)₂(H₂O)] (3), have been synthesized and characterized.

Keywords:

• N-Heterocyclic ligand
• Cadmium(II)
• Crystal structure
• Photoluminescence
• Supramolecular isomers

Additional information

Funding

This work was supported by National Natural Science Foundation of China [grant number 20971060], [grant number 21101018]; the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Natural Science Foundation of State Key Laboratory of Coordination Chemistry.