Modulated Synthesis of Zr-Based Metal-Organic Frameworks: From Nano to Single Crystals

• Published in: Chemistry : a European journal Vol. 17; no. 24; pp. 6643 - 6651
• Main Authors: Schaate, Andreas, Roy, Pascal, Godt, Adelheid, Lippke, Jann, Waltz, Florian, Wiebcke, Michael, Behrens, Peter
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 06-06-2011; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Acids; Chemistry; metal-organic frameworks; microporous materials; modulation approach; nanoparticles; Single crystals; zirconium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201003211

We present an investigation on the influence of benzoic acid, acetic acid, and water on the syntheses of the Zr‐based metal–organic frameworks Zr–bdc (UiO‐66), Zr–bdc–NH2 (UiO‐66–NH2), Zr–bpdc (UiO‐67), and Zr–tpdc–NH2 (UiO‐68–NH2) (H2bdc: terephthalic acid, H2bpdc: biphenyl‐4,4′‐dicarboxylic acid, H2tpdc: terphenyl‐4,4′′‐dicarboxylic acid). By varying the amount of benzoic or acetic acid, the synthesis of Zr–bdc can be modulated. With increasing concentration of the modulator, the products change from intergrown to individual crystals, the size of which can be tuned. Addition of benzoic acid also affects the size and morphology of Zr–bpdc and, additionally, makes the synthesis of Zr–bpdc highly reproducible. The control of crystal and particle size is proven by powder XRD, SEM and dynamic light scattering (DLS) measurements. Thermogravimetric analysis (TGA) and Ar sorption experiments show that the materials from modulated syntheses can be activated and that they exhibit high specific surface areas. Water proved to be essential for the formation of well‐ordered Zr–bdc–NH2. Zr–tpdc–NH2, a material with a structure analogous to that of Zr–bdc and Zr–bpdc, but with the longer, functionalized linker 2′‐amino‐1,1′:4′,1′′‐terphenyl‐4,4′′‐dicarboxylic acid, was obtained as single crystals. This allowed the first single‐crystal structural analysis of a Zr‐based metal–organic framework.
Modulated crystallinity: Nanocrystals of varying sizes of UiO‐66 (Zr–bdc metal–organic framework (MOF)), individual microcrystals of UiO‐67 (Zr–bpdc MOF) and the first single crystal of a Zr‐based MOF containing a long linker (Zr–tpdc–NH2 MOF) were obtained (see figure). The last one allowed, for the first time, a single‐crystal diffraction study of a Zr‐based MOF. (H2bdc: terephthalic acid, H2bpdc: biphenyl‐4,4′‐dicarboxylic acid, H2tpdc: terphenyl‐4,4′′‐dicarboxylic acid.)