Pitfalls in the location of guest molecules in metal-organic frameworks

Recently, Wang B. et al. reported a zirconium metal-organic framework (MOF) with high sensing abilities towards polychlorinated dibenzo-p-dioxins1. The sensing mechanism is based on fluorescence quenching from the dioxin-loaded MOF. The structure of the framework with the absorbed guest molecules (2,3-dichlorodibenzo-p-dioxin, BCDD) has been determined via single-crystal X-ray diffraction (XRD). Based on these measurements, the authors discuss the host-guest interactions. The quality of the diffraction data, however, does not allow to reliably determine the presence of BCDD in the pores.