Solvent-induced secondary building unit (SBU) variations in a series of Cu(ii) metal–organic frameworks derived from a bifunctional ligand

Abstract

The role of auxiliary solvents in the formation of metal–organic frameworks (MOFs) has been studied for a series of copper-based framework systems. Herein we show the formation of three different 3D ordered frameworks with the formulae {[Cu₄(cpt)₄Cl₄]·2DMF·dioxane·3H₂O}_n (1), {[Cu₈(cpt)₄(Hcpt)₂Cl₇(μ₃-OH)₂(H₂O)₄]Cl₃·4CH₃CN}_n (2), and {[Cu₈(cpt)₄Cl₄(μ₃-OH)₂(μ₄-O)₂]Cl₂·4H₂O·2CH₃CN·3MeOH}_n (3) [Hcpt = 4-(4-carboxyphenyl)-1,2,4-triazole], respectively, from the same reaction mixture through varying auxiliary solvents of the medium. These MOFs were fully characterized by single-crystal X-ray diffraction, showing interesting secondary building unit (SBU) variations. The varied SBUs not only bring different framework architectures to these MOFs, but also affect their framework stability. Gas sorption studies of MOF 3 reveal high CO₂–N₂ selectivity at 298 K and 0.16 bar (a typical partial pressure of CO₂ in an industrial flue gas). A high isosteric heat of adsorption (Q_st) at zero loading (53 kJ mol⁻¹) was also observed in MOF 3.