Thermal behavior of volatile palladium(II) complexes with tetradentate Schiff bases containing propylene-diimine bridge

Palladium(II) complexes with tetradentate Schiff bases, Pd(acacpda)( I ) and Pd(acacdmpda)( II ) (acacpda 2− — N , N ′-(propylene)-bis(acetylacetoneiminato-), acacdmpda 2− — N , N ′-(2,2-dimethylpropylene)-bis(acetylacetoneiminato-)), have been synthesized, purified and characterized by elemental analysis, IR and NMR spectroscopy. Complex I was obtained for the first time, and its solid-state structure was investigated by single-crystal X-ray diffraction. It has a discrete molecular structure with the Pd 2+ ion being in a distorted square-planar coordination environment formed by N and O atoms of the acacpda 2− ligand. The thermal properties of complexes I and II in condensed phase were investigated by thermogravimetry. Compound II transfers into the gas phase almost completely, while compound I evaporates with a partial decomposition. The temperature dependences of saturated vapor pressure were measured by the flow method in the temperature intervals (423–457) and (422–478) K for I and II , respectively. Both complexes were shown to exhibit an excellent stability upon sublimation. The thermodynamic parameters of sublimation processes were calculated to be: Δ sub H 440 = (133 ± 4) kJ mol −1 , Δ sub S 440 0 = (210 ± 9) J (mol K) −1 for I , Δ sub H 450 = (135 ± 1) kJ mol −1 , Δ sub S 450 0 = (218 ± 3) J (mol K) −1 for II . It has been found that the complex II with a more bulky Schiff base ligand possesses slightly higher vapor pressure values as compared to I , which is probably due to the lower contribution of weak intermolecular interactions occurring in the crystal structure of II .