Pentamers of formic acid

The potential energy surface of the formic acid pentamer is explored with hybrid density functional theory calculations. The lowest-energy structures include several folded rings, but planar or quasi-planar rings in which one or more monomeric units are in the E conformation, and planar structures consisting of the lowest-energy trimer and dimer are also prominent structural motifs. C-H⋯O bonds play a larger role than in trimers and tetramers. A planar ring is the most stable structure by the energy and enthalpy criteria.