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 Pd2+ 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: H-sub(440)=(133 +/- 4)kJmol(-1), (sub)S0=(210 +/- 9)J(molK)(-1) for I, H-sub(450)=(135 +/- 1)kJmol(-1), (sub)S0=(218 +/- 3)J(molK)(-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.