Predicting experimental complexation-induced changes in 1H NMR chemical shift for complexes between metalloporphyrins and ligands using the Ab initio/GIAO-HF methodology

Ab initio calculations were carried out on several metalloporphyrins complexed to several ligands. The experimental spectra of metalloporphyrin–ligand complexes show large upfield shifts for the ligand proton signals compared to the free ligand. These shifts are caused by the proximity of the porphyrin π-system. The 1H NMR chemical shifts of these complexes were computed via ab initio calculations using the GIAO method at several levels of theory and the obtained values agree satisfactorily with experimental results.