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

Abstract

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 Q_st 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.