Polyether phases of formic acid revealed under high pressure.

Evolutionary structure searches reveal that at 20 GPa, formic acid (FA) transforms to an orthorhombic ether-chain polymer phase, ruling out hydrogen bond symmetrization, followed by a novel crowned cyclic-ether tetragonal phase above 60 GPa. Emergence of characteristic polyether and new OH stretching modes in infrared experiments validate the findings. Resemblance of polymer chain with a cosmopolymer polyoxymethylene, shows an engrossing multifaceted evolution of FA.