Electronic properties and metal-ligand bonding situation in Eu(III) complexes containing tris(pyrazolyl)borate and phenantroline ligands

In this paper we report the preparation, characterization (infrared absorption spectroscopy, photoluminescence, and thermogravimetric analysis), and DFT based electronic structure calculations (GKS-EDA), used to shed light into the metal-ligand bonding situation, of a set of Eu3+ complexes containing tris-(pyrazolyl)borate “scorpionate” (Tp) and phenantroline (phen) as ligands in different proportions. The Infrared results point out that the complexes [Eu(phen)(Tp)3] (Eu/phen/Tp molar ratio 1:1:3) is not obtained, suggesting that Tp ligand displaces phen ligand leading to the formation of [Eu(Tp)3] (molar ratio 1:3). Photoluminescence results, including emission and excitation spectra give support to the vibrational spectra interpretation, confirming that three ligands Tp displace the ligand phen, to form [Eu(Tp)3]. GKS-EDA results show that Eu3+---Tp interactions are much more stabilizing than Eu3+---phen interactions, in agreement with the experimental evidences that the third Tp remove phen from the Eu3+ coordination environment.