Spin Density Studies of Tetrahedral Cu(II) Ions Doped into Porous Zeolitic Imidazolate Frameworks

Multifrequency electron paramagnetic resonance (EPR) methodologies combined with density functional theory (DFT) modeling are used to monitor the local structure of cupric ions doped into a porous zeolitic imidazolate framework (ZIF-8). Because of the constraint imposed by the ZIF-8 framework, Cu2+ ions substituting Zn2+ sites assume a highly distorted tetrahedral geometry. The 14N electron nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) experiments confirm the incorporation of copper ions in the framework position, providing the first detailed electronic and structural analysis of cupric ions in ZIF materials. The experimental findings are validated by DFT modeling which gives an atomistic picture of the Cu2+-doped material.