X-ray crystal structures and thermal behaviour of two volatile bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)barium-(azapolyether) complexes

Two novel Ba(hfac)(2) . (azapolyether) [hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionato] adducts have been synthesized and characterized by single crystal X-ray crystallography, differential scanning calorimetry and spectroscopic methods. Compound 1 contains the macrocyclic ligand 1-aza-4,7,10,13,16-pentaoxacyclooctadecane [1-aza-18-crown-6], while compound 2 contains the acyclic ligand 8-aza-2,5,11,14-tetraoxapentadecane [8-azatetraglyme]. In both compounds the azapolyether ligands coordinate a central barium atom in a meridional fashion, with the hfac ligands on opposite sides of the neutral ligand plane. The basic coordination geometries of complexes 1 and 2 are thus analogous to those in most of the barium beta-diketonate polyether and polyamine adducts structurally characterized in earlier work. However, closer examination of their crystal and molecular structures reveals several interesting features, including markedly different geometries for the two non-equivalent molecules in the unit cell of 1, and also relatively long hfac oxygen to barium bond lengths in this complex. Both 1 and 2 sublime at ca 135 degrees C and 0.05 Torr, with 2 showing much higher volatility. 1 melts with decomposition at ca 240 degrees C, while 2 undergoes melting with minimal decomposition at ca 170 degrees C. Both compounds have endothermic solid state transitions between 25 degrees C and their melting temperatures. The kinetically slow solid state transition of 1 has been studied in detail, demonstrating its phenomenological similarity to a previously studied process in Ba(hfac)(2) . (18-crown-6). Combined with earlier results, the current work suggests that the solid state transitions of 1 and Ba(hfhc)(2) . (18-crown-6) may involve isomerization reactions in which the barium coordination geometry changes fundamentally.