⁶³Cu-NMR in pristine HKUST-1 MOF: static and dynamic effects near the Cu environment

NMR Spectroscopy is being used to explore magnetic and charge properties of the Cu(II)-based metal-organic framework (MOF) HKUST-1 and the change in conductivity that occurs between pristine HKUST-1 and HKUST-1 with tetracyano-quinodimethane (TCNQ) infiltration. The pulse NMR technique can be used to examine the interactions between the nuclei and the unpaired electrons in paramagnetic Cu(II) in pristine HKUST-1. This will allow for further understanding of the effect on the conductivity of the material when the pores of the MOF are occupied by TCNQ. Here we report on the ⁶³Cu-NMR of pristine HKUST-1. We find that the ⁶³Cu-NMR spectral linewidth in this system increases with decreasing temperature as would be expected for dipolar interactions of the paramagnetic Cu(II) ions with the nuclear moments. Surprisingly, we also find that the ⁶³Cu line-shift with respect to a CuBr reference is very close to that of copper metal. To shed light on this intriguing experimental result, we will present preliminary measurements of lineshape, spin-lattice and spin-spin relaxation times as functions of temperature and applied magnetic field in pristine HKUST-1.