Electronic structure and optical properties of Sm(III) and Eu(III) complexes with hexamethylphosphoramide

Nitrate complexes Ln(NO3)3 of Sm(III) and Eu(III) lanthanides with three neutral ligands HMPA (OP(NMe2)3) possessing triboluminescent properties were studied by X-ray photoelectron spectroscopy (XPS MgKα) and quantum chemistry (DFT/TDDFT). Interpretation of the bands of XPS spectra of the valence levels and core levels was carried out using the calculated energies and localization of the Kohn-Sham orbitals. Using the DFT/TDDFT methods the influence of HMPA molecules on the electronic structure of lanthanide ion nitrate complexes was studied and the electronic effects of adduct formation are described. The nature of the bond of nitrate complexes with neutral molecules was revealed. The binding energy of Ln(NO3)3 (Ln = Sm, Eu) with three HMPA molecules was determined theoretically (Sm(NO3)3(HMPA)3–5.17 eV, Eu(NO3)3(HMPA)3–4.11 eV). The relationship of the electronic structure with the absorption and excitation spectra, optical characteristics and its role in reducing the probability of the energy transfer from ligands to metal within the LMCT (ligand-to-metal charge-transfer) model is shown. The experimental and theoretical absorption spectra were obtained for the studied adducts possessing promising solubility properties in water. Prospects of further research of the intermolecular layers are shown for the crystals under study.