Definitive Molecular Level Characterization of Defects in UiO-66 Crystals

The identification and characterization of defects, on the molecular level, in metal‐organic frameworks (MOFs) remain a challenge. With the extensive use of single‐crystal X‐ray diffraction (SXRD), the missing linker defects in the zirconium‐based MOF UiO‐66, Zr6O4(OH)4(C8H4O4)6, have been identified as water molecules coordinated directly to the zirconium centers. Charge balancing is achieved by hydroxide anions, which are hydrogen bonded within the pores of the framework. Furthermore, the precise nature of the defects and their concentration can be manipulated by altering the starting materials, synthesis conditions, and post‐synthetic modifications.This work, including synthesis, characterization, and crystal structure analysis was funded by BASF SE (Ludwigshafen, Germany) and the U.S. Department of Defense, Defense Threat Reduction Agency (HDTRA 1‐12‐1‐0053). Work performed at the Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE‐AC02–05CH11231. F.G. acknowledges the Spanish Ministry of Economy and Competitiveness for funding through the Juan de la Cierva program