Spectroscopic interrogations of isostructural metalloporphyrin-based metal-organic frameworks with strongly and weakly coordinating guest molecules

Two isostructural metal-organic frameworks based on cobalt(II) and nickel(II) metalloporphyrin linkers, Co-PCN222 and Ni-PCN222, are investigated using resonance Raman and X-ray absorption spectroscopy. The spectroscopic consequences of framework formation and host–guest interaction with weakly and strongly coordinating guest molecules (acetone and pyridine) are assessed. Structure sensitive vibrational modes of the resonance Raman spectra provide insights on the electronic and structural changes of the porphyrin linkers upon framework formation. XANES and EXAFS measurements reveal axial binding behavior of the metalloporphyrin units in Co-PCN222, but almost no axial interaction with guest molecules at the Ni porphyrin sites in Ni-PCN222.