Polymorphism in a Multicomponent Crystal System of Trimesic Acid and t-Butylamine

Abstract

Polymorphism in a multicomponent crystal system of trimesic acid (TMA) and t-butylamine (TBA) with stoichiometry (TMA)2(TBA)3 is reported, with the discovery and structural characterization of two polymorphs with rhombohedral and triclinic symmetries. In each polymorph, the TBA molecules exist as protonated cations, and the two independent TMA molecules are deprotonated by loss of a total of three protons (the specific protonation state of each TMA anion depends on the interpretation of hydrogen-bond disorder in the crystal structure). Both structures are based on sheets of TMA anions arranged in a hydrogen-bonded honeycomb network; these sheets are essentially planar in the rhombohedral polymorph but corrugated in the triclinic polymorph. The TBA cations are linked by hydrogen bonding to the TMA anions in this network, with the t-butyl groups occupying the void space within the honeycomb network and the regions of space between adjacent sheets. Periodic DFT-D calculations suggest that the rhombohedral polymorph is more energetically stable than the triclinic polymorph.