Abstract
Using gas sorption measurements at ambient temperatures and in situ neutron powder diffraction methods, we have studied the interaction strengths and coordination geometries of O2 and N2 near the non-occupied coordination site (open metal site) in the isostructural MOF structures of the CPO-27-M/M-MOF-74 series (with M = Co, Ni, Mn and Cu). Our experimental observations are compared to periodic quantum chemical model calculations. Contrary to recent computational studies, our results, both experimental and theoretical, unequivocally suggest rather weak interactions between the M(II) coordinatively unsaturated centers and the adsorbate molecules, being mainly dispersive and electrostatic in nature. As a consequence, they exclude significant orbital charge transfer effects that could lead to superoxide/peroxide formation. Calculated binding energies appear in good agreement with the measured isosteric heats of adsorption in the range of 10-20 kJ mol-1. These, relatively weak host-guest interactions, lead to a tilted end-on geometry in all of the investigated M(II)-guest molecule adducts.
| Original language | English |
|---|---|
| Pages (from-to) | 26346-26357 |
| Number of pages | 12 |
| Journal | Physical Chemistry Chemical Physics |
| Volume | 19 |
| Issue number | 38 |
| DOIs | |
| State | Published - 2017 |
Funding
Regarding neutron diffraction measurements on CPO-27-Mn and -Co: this work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. With respect to neutron diffraction measur-emnts on CPO-27-Cu and -Ni: we thank HZB for the allocation of neutron beamtime. Special thanks to Dr Dirk Wallacher for providing gas handling assistance at the HZB. This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883. During part of this work PAG has been supported by the Project ‘‘Beyond Everest’’ under EU programme REGPOT-2011-1. MHR and PDCD acknowledge the support from the Research Council of Norway through the FRINATEK program (grant 221596) and ISP-KJEMI program (grant 209339). MF wishes to acknowledge funding from the European Union’s Seventh Framework Programme (FP7/2007–2013) under Grant Agreement No. 290605 (PSIFELLOW/COFUND).