A series of solid ternary lanthanide complexes with the general formula Ln(BA)3(PIP) (Ln = La–Lu, except Pm) were prepared with hydrated lanthanide chloride, benzoic acid (BA), and 2-phenylimidazo[4,5-f]1,10-phenanthroline (PIP). These obtained complexes were characterized by means of elemental analysis, EDTA volumetric analysis, IR spectroscopy, X-ray powder diffraction, and mass spectroscopy. The thermal decomposition mechanism of all complexes in the solid state was explored using TG–DTG techniques under dynamic flow of air atmosphere. Moreover, the constant-volume combustion energies, ∆c U, of the complexes were determined by a precise rotating-bomb calorimeter (RBC-type II) at 298.15 K. Their standard molar enthalpies of combustion, $$ \Delta _{\text{c}} H_{\text{m}}^{\uptheta} $$ , and standard molar enthalpies of formation, $$ \Delta_{\text{f}} H_{\text{m}}^{\uptheta} $$ , were calculated.