A Cd-based crystalline network material: catalytic properties and post-synthetic metal-ion metathesis with enhanced stability and gas sorption behaviour

Abstract

This study presents the synthesis of a Cd(II) based hydrophobic three dimensional crystalline network material (CNM), [Cd₃(L)₂(LH)₂(bpe)₂], {L = {4,4′-(hexafluroisopropylidine)bis(benzoate)} and 1,2-di(4-pyridyl) ethylene (bpe)}, 1(Cd), by employing the slow-diffusion method. The three-dimensional structure of 1(Cd) was determined by single crystal X-ray diffraction and characterized by powder X-ray diffraction (PXRD), FT-IR spectroscopy and thermogravimetric analysis (TGA). Subsequently, post-synthetic modification of 1(Cd) with Cu(II) at room temperature led to the formation of isostructural 1(Cu) with partial substitution. This transformation, unattainable through de novo synthesis, was monitored using energy dispersive X-ray analysis (EDX), PXRD, FT-IR spectroscopy, and through visual observation confirming a single crystal to single crystal metal exchange. The modified material, 1(Cu), exhibited red-shifted emission with enhanced thermal stability and a tenfold increase in N₂ uptake. Furthermore, the catalytic potential of 1(Cd) in aza-Michael addition reactions of α,β-unsaturated olefins to nucleophilic aromatic/aliphatic amines was demonstrated successfully under ambient conditions. This approach employed a heterogeneous and acid–base free methodology, showcasing the versatility and effectiveness of 1(Cd) as a catalyst.