Continuous-Wave Single-Crystal Electron Paramagnetic Resonance of Adsorption of Gases to Cupric Ions in the Zn(II)-Doped Porous Coordination Polymer Cu2.965Zn0.035(btc)2

Abstract

Continuous-wave X-band electron paramagnetic resonance with dielectric resonators has successfully been applied to small single crystals of the metal–organic framework HKUST-1 and Cu2.965Zn0.035(btc)2 to investigate the structure of paddle-wheel building blocks with pure Cu/Cu and mixed Cu/Zn pairs. The local paramagnetic Cu2+ ion probes were used to identify the magnetic g and A tensor orientations with respect to the crystal axes. We were able to monitor changes in these tensor orientations by EPR at gas adsorption on MOFs for the first time. We explored the spectral simulations of the spin Hamilton parameters of the single crystals and found results similar to those in previous studies of powder samples, but moreover, the tensor orientations are influenced upon gas adsorption, which is represented by a distinct line broadening effect in the angular resolved single-crystal EPR spectra. The as-synthesized, dehydrated, carbon dioxide-adsorbed, carbon monoxide-adsorbed, methanol-adsorbed, and reactivated s...