Synthetic, spectral, structural and catalytic activities of 3-D metal format/acetate framework materials for CO2 conversion

Abstract

Two new coordination polymers [Cu₂(HCO₂)₂(H₂O)₂]_n(1), and [Na{Ni(CH₃CO₂)₂(CH₃CO₂H)}]_n (2) were synthesized using a mild solution chemistry approach and characterized spectroscopically, and the molecular structures of 1, and 2 were determined by the single crystal X-ray diffraction technique. Bridged by CHOO⁻/CH₃COO⁻, M ions form a three-dimensional distorted perovskite-like structure. The solid-state structure revealed that 1 is an infinite three-dimensional (3D) motif in which Cu(II) are bridged by formate in a κ¹ manner and four water molecules, while 2 is also an infinite three-dimensional (3D) structure having two nickel coordinated to four acetates in a κ² manner and one acetic acid that further interact with sodium ions. 1 has a 6-connected uninodal map topology with the point symbol of {4^4.6^10.8} whereas 2 has a 4-connected uninodaldia net with sqc6 topology and point symbol {6^6}. All the motifs (1–2) could serve as excellent catalysts for CO₂-based chemical fixation. 2 shows high efficiency for CO₂ cycloaddition with small epoxides but its catalytic activity decreases sharply with the increase in the size of epoxide substrates. The results indicated that the copper(II) and nickel(II)–sodium motifs catalyzed CO₂ cycloaddition of small substrates was carried out within the framework, while large substrates could not enter into the framework for catalytic reactions. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO₂ cycloaddition make 2, a promising heterogeneous catalyst for carbon fixation.