Structures of the formic acid trimer

Hybrid density functional calculations are used to locate 33 local minima on the potential energy surface of the formic acid trimer. Additional computations are performed for the 14 lowest-energy structures to assess their sensitivity to enlarging the basis set and to varying the density functional. Energies and enthalpies show that the global minimum is a planar structure consisting of the lowest-energy dimer bound to the third monomer by a strong O–H⋯O bond. However, a planar, symmetric ring structure has the lowest Gibbs free energy.