Rational design microporous pillared-layer frameworks: syntheses, structures and gas sorption properties

Abstract

The solvothermal reactions of nickel nitrate hexahydrate, aromatic carboxylic acids, and either 4,4′-bipyridine (bipy) or pyrazine (pyz) produced three open-framework compounds, namely, Ni(HBTC)(pyz)·3DMF 2 (BTC = 1,3,5-benzentricarboxylate, DMF = N,N′-dimethylformamide), Ni₂(BTEC)(bipy)₃·3DMF 3 (BTEC = 1,2,4,5-benzenetetracarboxylate), together with previously reported Ni(HBTC)(bipy)·3DMF 1. Compound 2 is the product when pyz pillars replace bipy pillars in the reaction of 1, and it is a 3D porous network where honeycomb grid layers constructed by Ni-BTC groups are interlinked by pyz pillars. When the BTEC ligand takes the place of BTC ligand in the system, compound 3 is obtained and it is a 3D connectivity with 1D channels where Ni-BTEC chains are interlinked by bipy ligands. The three compounds feature permanent porosity, which was confirmed by N₂ adsorption isotherm measurement, and the architectural features of 1–3 can be ascribed to pillared-layer motifs. Furthermore, hydrogen adsorption measured at 77 K for 1 shows an excess uptake of 3.03 wt% at 20 bar. Details of the synthesis conditions, crystal structures and property measurements of each new compound are described.