Amide-containing zinc(II) metal–organic layered networks: a structure–CO2 capture relationship

The self-assembly of zinc–organic coordination polymers [Zn2(1,3-bdc)2(bpda)2]·3DMF·0.5H2O (1, 1,3-bdc = 1,3-benzenedicarboxylate; bpda = N,N′-bis(pyridine-4-yl)-1,4-benzenedicarboxamide) and [Zn2(1,4-ndc)(dmc)2(bpda)2] (2, 1,4-ndc = 1,4-naphthalenedicarboxylate; dmc = dimethylcarbamate) through mixed-ligand coordination under hydro(solvo)thermal conditions is reported. Both compounds 1 and 2 are made up of a two-dimensional layered network with a decorated 44-sql topology from the associated dinuclear two-blade paddlewheel building units. The bis-amide groups of the bpda ligands in the layered structures of 1 and 2 are sheltered and participate in multiple hydrogen-bonding interactions. Compounds 1 and 2 are both highly thermally stable at temperatures over 300 °C and exhibit solid-state luminescence properties. In comparison with the CO2 adsorption behavior of the related compound {[Zn4(1,4-bdc)4(bpda)4]·5DMF·3H2O}n (3, 1,4-bdc = 1,4-benzenedicarboxylate), both the desolvated sample of 1 and the thermally-activated sample of 2 show a lower CO2 uptake capacity and a decreased Qst trace with increasing CO2 uptake. These results show that no meaningful cooperative binding occurs between the amide groups and CO2 molecules in the condensed 2D structures of 1 and 2. By varying the dicarboxylate ligand from 1,3-bdc, 1,4-ndc to 1,4-bdc, the amide-functionalized products 1–3 induce subtle changes in their structures. In particular, the intimate interrelationship between the structural characteristics of amide groups and the CO2 adsorption behavior of such compounds is clearly demonstrated.