High-pressure studies of three polymorphs of a palladium(II) oxathioether macrocyclic complex

The three reported phases of the mononuclear macrocyclic Pd^II complex [PdCl₂([9]aneS₂O)] [(1); [9]aneS₂O = 1-oxa-4,7-dithiacyclononane] were each studied up to pressures exceeding 9 GPa using high-pressure single-crystal X-ray diffraction. The α- and γ-phases both exhibit smooth compression of the unit-cell parameters with third-order Birch–Murnaghan bulk moduli of 14.4 (8) and 7.6 (6) GPa, respectively. Between 6.81 and 6.87 GPa β-[PdCl₂([9]aneS₂O)] was found to undergo a reversible transition to a phase denoted as β′ and characterized by a tripling of the unit-cell volume. Across the phase transition, rearrangement of the conformation of the bound macrocycle at two of the resulting three unique sites gives rise to an extensively disordered structure.