Structure and Thermodynamical Properties of Metformin Salicylate

The behavior under thermal conditions
of the cocrystal formed by
metformin and salicylic acid was studied by DSC, crystallography (single-crystal),
and powder diffraction (WAXS). Metformin salicylate crystallizes in
space group P21/c, with
the salicylate anion showing a planar structure, stabilized by strong
intramolecular hydrogen bonds. The more flexible metformin cations
link through the oxygen atoms of salicylate, forming a dense hydrogen-bonding
network. The compound exists initially as a salt, metformin salicylate,
but after melting and cooling, it is transformed into a glass form
that crystallizes and melts again, showing different behaviors depending
on the heating rate.