A series of isomorphous Metal-Organic Frameworks with rtl topology – Metal distribution and tunable sorption capacity via substitution of metal ions

• Isomorphous MOFs with related linkers and/or different M2+ ions are presented.
• Synthesis of pure and mixed metal compounds.
• SEM-EDX analyses provide insight into the metal ion distribution.
• Sorption properties can be tuned by metal ion substitution.

The formation and analysis of ten microporous triazolyl isophthalate based MOFs, including nine isomorphous and one isostructural compound is presented. The compounds 1M–3M with the general formula [M(R1-R2-trz-ia)]∞3 ·x H2O (M2+ = Co2+, Cu2+, Zn2+, Cd2+; R1 = H, Me; R2 = 2py, 2pym, prz (2py = 2-pyridinyle; 2pym = 2-pyrimidinyle; prz = pyrazinyle)) crystallize with rtl topology. They are available as single crystals and also easily accessible in a multi-gram scale via refluxing the metal salts and the protonated ligands in a solvent. Their isomorphous structures facilitate the synthesis of heteronuclear MOFs; in case of 2M, Co2+ ions could be gradually substituted by Cu2+ ions. The Co2+:Cu2+ ratios were determined by ICP-OES spectroscopy, the distribution of Co2+ and Cu2+ in the crystalline samples are investigated by SEM-EDX analysis leading to the conclusions that Cu2+ is more favorably incorporated into the framework compared to Co2+ and, moreover, that the distribution of the two metal ions between the crystals and within the crystals is inhomogeneous if the crystals were grown slowly. The various compositions of the heteronuclear materials lead to different colors and the sorption properties for CO2 and N2 are dependent on the integrated metal ions.

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