Conformationally Assisted Negative Area Compression in Methyl Benzoate

Methyl benzoate (MB) freezes isobarically at 0.1 MPa below 261 K and isothermally at 296 K above 0.35 GPa in phase α, with the molecules in energetically unfavorable twisted conformation. At 0.54 GPa, phase α undergoes a most unusual isostructural transition to a new β phase. At the transition point the crystal is compressed along [ x ] and expands along plane yz, which is analogous to negative Poisson’s ratio of −2.05. Above 0.54 GPa, the MB molecules assume the planar conformation, by 2.70 kJ mol –1 more stable than the twisted conformation at ambient-pressure, and arene and methyl H-donors are exchanged in the C–H···π bonding pattern. The interplay between the crystal strain, molecular conformation and the intermolecular interactions has been established.