Low temperature phase transitions as a representation of structural flexibility of alkaline earth mixed ligand β-diketonates

Abstract The low temperature phase transitions of mixed ligand complexes [Ca(hfa) 2 (diglyme)(H 2 O)] ( I ), [Sr(hfa) 2 (diglyme)(H 2 O)] ( II ) and [Ba(hfa) 2 (diglyme) 2 ] ( III ) (Hhfa = hexafluoroacetylacetone, diglyme = 2,5,8-trioxanonane) have been detected by differential scanning calorimetry and X-ray diffraction. A comparison of the single-crystal XRD data collected at low and room temperatures shows that these transitions occur due to conformational and positional changes of the ligands in the coordination polyhedra of the central alkaline earth ions, and represent the structural flexibility of I–III . The revealed effects influence the lattice energy of alkaline earth complexes with a structural flexible coordination polyhedron and should be taken into account during theoretical estimation of the thermodynamic properties based on low temperature crystallographic data.