Syntheses and Crystal Structures of Three Pyrrole-2-Carboxylate with C3-Symmetry.

The reaction of three equivalents of 2-(trifluoroacetyl)pyrrole with triols [RC(CH2OH)3, R=H, CH3, CH2OH] produce triesters of pyrrole-2-carboxylic acid (1–3, respectively) which crystallize in space groups with molecular C3 symmetry coinciding with the crystallographic symmetry (averaged in the case of R=CH2OH). All are unsolvated. Compound 1 crystallizes in space group P-3 and 2 and 3 in space group P-43n. In all three, molecules form three R22(10) Hydrogen-bonded interactions between syn pyrrole N-H and carboxyl C = O on neighboring molecules. In 1, molecules are linked into infinite chains and hexamolecular rings, and the cavity at the center of the rings (site symmetry − 3) is too small to harbor a guest molecule. In 2 and 3, supramolecular assemblies radiate from four molecules with methyl and hydroxymethyl groups at tetrahedral sites in the cubic structures. Computations confirm the importance of Hydrogen-bonding in these assemblies which add to the hundreds of similar pyrrole carboxylates previously described. Applications of the R22(10) hydrogen bond motif formed between two pyrrole-2-carboxylate moieties in the design of hydrogen bonded framework. Three tripodal pyrrole-2-carboxylate compounds were synthesized, and their structure were characterized by X-ray crystallography. The three compounds self-assembled into hexamer or cubic supramolecular structures. The relibility of the motif was also proved by DFT calculations and search in Cambridge Structural Database (CSD). [ABSTRACT FROM AUTHOR]