Tuning the void volume in a series of isomorphic porous metal-organic frameworks by varying the solvent size and length of organic ligands.

A series of isomorphic metal-organic frameworks, namely, [Cd3(IN)4(N3)2(DMA)2]⋅2DMA (1), [Cd3(IN)4(N3)2(NMP)2]⋅2NMP (2), [Cd3(IN)4(N3)2(DMI)2]⋅2DMI (3), [Cd3(TP)4(N3)2(DMA)2]⋅4DMA⋅H2O (4), [Cd3(TP)4(N3)2(NMP)2]⋅4NMP⋅H2O (5), and [Cd3(TP)4(N3)2(DMI)2]⋅4DMI (6), where HIN = isonicotinic acid and HTP = 4-tetrazole pyridine, have been synthesized via solvothermal reaction with Cd(NO3)2⋅4H2O in three different solvents [N,N-dimethylacetamide (DMA), N-methylpyrrolidinone (NMP), and 1,3-dimethyl-2-imidazolidinone (DMI)]. Single-crystal X-ray structure analysis reveals that compounds 1-6 show threedimensional (3D) 6-connected nets with channels based on trinuclear cadmium clusters. The coordinated and lattice solvent molecules occupy the free void spaces of the channels. Induced by different solvent molecules, the solvent-accessible volumes of these MOFs are 3 > 2 > 1 and 6 > 5 > 4, which is consistent with the sizes of solvents (DMI > NMP > DMA). By comparing 1-3 with 4-6, the longer organic anion is beneficial to construct MOFs with larger porous sizes and higher solvent-accessible volumes. [ABSTRACT FROM AUTHOR]