Thermodynamic properties of mixed-ligand rare earth pivalates

For structurally characterized dinuclear rare earth pivalate complexes, Ln2(piv)6(Hpiv)6·Hpiv (Hpiv is pivalic acid, Ln = La (1), Sm (2), Eu (3), and Gd (4)), Tb2(piv)6(Hpiv)6 (5), (bpy)2Ln2(piv)6, (bpy = 2,2′-bipyridine, Ln = Sm (6), Eu (7), Gd (8), and Er (9)), and (phen)2Ln2(piv)6 (phen = 1,10-phenanthroline, Ln = Sm (10), Eu (11), and Tb (12)), the temperature dependences of the heat capacities were measured by adiabatic and differential scanning calorimetry, and the thermodynamic functions Cp0(T), S0(T), Ф0(T), and H0(T) − H0(0) were calculated. The Cp0(T) curves for the complexes with pivalic acid and 2,2′-bipyridine show anomalies, whereas no structural changes are observed for the complexes with 1,10-phenanthroline between the temperature range from 5 K to the temperature of the ligand removal.

► 12 rare earth pivalate complexes were measured by adiabatic calorimetry and DSC.
► Thermodynamic functions in the studied temperature range were calculated.
► No phase transitions for the (phen)2Ln2(piv)6 were found from 5 K to temperature of ligand removal.