Synthetic, spectral, structural and catalytic activity of infinite 3-D and 2-D copper() coordination polymers for substrate size-dependent catalysis for CO conversion

Two copper( ii ) coordination polymers, viz. [Cu 2 (OAc) 4 (μ 4 -hmt) 0.5 ] n ( 1 ) and [Cu{C 6 H 4 (COO − ) 2 } 2 ] n ·2C 9 H 14 N 3 ( 2 ), have been synthesized solvothermally and characterized. The solid-state structure reveals that 1 is an infinite three-dimensional (3D) motif with fused hexagonal rings consisting of Cu( ii ) and hmt in a μ 4 -bridging mode, while 2 is an infinite two dimensional (2D) motif containing Pht −2 in a μ 1 -bridging mode. CP 1 has a two-fold interpenetrated diamondoid network composed of 4-connected sqc6 topology with the point symbol of {6 6 }, while 2 has a Shubnikov tetragonal plane network possessing a 4-connected node with an sql topology with a point symbol of {4 4 ·.6 2 }-VS [4·4·4·4·*·*]. Both CPs 1 and 2 serve as efficient catalysts for CO 2 -based chemical fixation. Moreover, 1 demonstrates one of the highest reported catalytic activity values (%yield) among Cu-based MOFs for the chemical fixation of CO 2 with epoxides. 1 shows high efficiency for CO 2 cycloaddition with small epoxides but its catalytic activity decreases sharply with the increase in the size of epoxide substrates. The catalytic results suggested that the copper( ii ) motif-catalyzed CO 2 cycloaddition of small substrates had been 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 CO 2 cycloaddition make 1 a promising heterogeneous catalyst for carbon fixation and it can be used as a recoverable stable heterogeneous catalyst without any loss of performance. The solvent-free synthesis of the cyclic carbonate from CO 2 and an epoxide was monitored by in situ FT-IR spectroscopy and an exposed Lewis-acid metal site catalysis mechanism was proposed. Two copper( ii ) coordination polymers have been synthesized and used as substrate size-dependent catalyst for CO 2 cycloaddition with epoxides.