Determination of ligand field splitting in lanthanide(iii) monoporphyrinato complexes

The 4f-electronic structures of the ground multiplet states of a series of lanthanide(iii) monoporphyrinato complexes with a cyclen as the capping ligand [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, and Yb; TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) have been determined using experimental NMR and magnetic susceptibility data. Magnetic susceptibilities of the microcrystalline samples of [Ln(TPP)(cyclen)]Cl were measured in the range of 1.8-300 K. NMR signals corresponding to the protons on the porphyrin ring show marked paramagnetic shifts (lower = Tb, Dy, Ho, and Yb; higher = Er and Tm) in comparison with the diamagnetic Y congener. A set of ligand-field parameters that simultaneously reproduces the magnetic susceptibilities and the paramagnetic shifts has been determined by using a self-developed multidimensional optimization program. In addition, CASSCF calculations were carried out for further insight into their electronic structures.