Synthesis of mixed ligand complexes [Lu(acac)3phen] 1 and [Lu(acac)3dipy] 2 was carried out. Complexes 1 and 2 have mononuclear structures with six oxygen atoms and two nitrogen atoms in the coordination sphere of the central Lu3+ ion. Theoretical calculations of structures and properties of mixed ligand complexes [Ln(acac)3Q] (where Ln=La, Gd, Lu; Q=phen, dipy) were performed at the DFT/B3PW91 level. The natural bond orbital analysis (NBO) was used to characterize the electronic structures of complexes. The features of crystal structures of complexes [Ln(acac)3Q] in lanthanide row were explained taking into account the bond nature. The influence of both nature of central lanthanide ion and neutral additional ligand on structures and properties of complexes under investigation is discussed. The Ln(acac)3—Q bond energy was found to be decreased from La-based complexes to Lu-based compounds. Thus, the unexpected inverted electrostatic trend, i.e. a decrease in stability along the lanthanide series, has been found out.