Synthesis, characterization, ion-exchange, and catalytic properties of three isostructural copper(II) coordination polymers with a flexible bis(triazole) ligand

Abstract

Ion-exchange processes are shown to occur in several coordination polymers (CPs) and their unique subclass of metal-organic frameworks (MOFs). The development of fast and economical routes to stable ion-exchange CP materials is important to broaden the range of applications for these materials. Herein, we report a greatly improved synthesis and coordinated anion exchange of three new copper(II) coordination polymers [Cu(Fbtx)2(NO3)2]n (1), [Cu(Fbtx)2(BF4)2]n (2) and [Cu(Fbtx)2(SO4)]n (3) (Fbtx ​= ​1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene) under the microwave-assisted hydrothermal conditions. The three Cu-CPs are crystallographically isostructural, exhibiting two-dimensional layered structures with the 44-sql topology. Complexes 1–3 display good thermal stability and excellent chemical stability in organic solvents and aqueous solutions with wide pH range of 1–13. The anion-exchange functions of the series of sql-type coordination networks were monitored by using powder X-ray diffraction, infrared spectroscopy and ion chromatography. The results revealed that these complexes can undergo anion-exchange under microwave irradiation, and the reversible exchange process depends on the size of the anions. These materials were demonstrated to be efficient heterogeneous catalysts for the direct carboxylation of 1-ethynylbenzene with CO2 under mild conditions, and various propiolic acids were synthesized in moderate to good yields under optimized reaction conditions. Moreover, the catalyst could be recycled up to five times with the retention of both catalytic activity and crystal structure.