The effect of pressure on the crystal structure of [Gd(PhCOO) 3(DMF)]n to 3.7 GPa and the transition to a second phase at 5.0 GPa

The effect of pressure on the crystal structure of the coordination polymer [Gd(PhCOO)3(DMF)]n has been studied to 5.0 GPa. At ambient pressure the structure is tetragonal (space group P42/n) with the polymers extending along the c-direction of the unit cell; successive Gd atoms are alternately bridged by four benzoates and by two benzoates; the coordination spheres of the metal atoms are completed by DMF ligands. This results in two different Gd⋯Gd repeats, measuring 3.8953(3) and 5.3062(3) Å, respectively. The polymer chains interact with each other via dispersion interactions, including a number of CH⋯π contacts to phenyl rings in which the H⋯ring-centroid distances are 3.19 to 3.28 Å. Up to 3.7 GPa the crystal remains in a compressed form of its ambient-pressure phase. The a-axis shortens by 7.7%, and the c-axis by 2.9%, the difference reflecting the greater ease of compression along the crystallographic directions mediated by weak intermolecular interactions. At ambient pressure the Gd-O distances span 2.290(2)-2.559(2) Å, with an average of 2.39(3) Å. At 3.7 GPa the corresponding parameters are 2.259(3) to 2.509(4) and 2.36(3) Å. The Gd⋯Gd distances shortened by 0.0467(4) and 0.1851(4) Å, and the CH⋯π distances span the range 2.76-2.90 Å. During compression a number of H⋯H contacts develop, the shortest measuring 1.84 Å at 3.7 GPa. On increasing the pressure to 5.0 GPa a phase transition occurred in which the shortest H⋯H contact is relieved by conversion of an edge-to-edge phenyl-phenyl contact into a π⋯π stacking interaction. The new phase is also tetragonal, space group P4, the inversion symmetry present in phase-I being lost in phase-II. The phase transition allows more efficient packing of ligands, and while the a-axis decreases in length the c-axis increases. This leads to Gd⋯Gd distances of 3.8373(4) and 5.3694(4) Å, the latter being longer than at ambient pressure. Gd-O distances at 5.0 GPa span the range 2.265(5) to 2.516(5) Å, with a mean of 2.36(2) Å. © The Royal Society of Chemistry 2010.