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Supramolecular Stabilization of Metastable Tautomers in Solution and the Solid State
Author(s) -
Juribašić Marina,
Bregović Nikola,
Stilinović Vladimir,
Tomišić Vladislav,
Cindrić Marina,
Šket Primož,
Plavec Janez,
Rubčić Mirta,
Užarević Krunoslav
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403543
Subject(s) - tautomer , supramolecular chemistry , chemistry , hydrogen bond , molecule , metastability , protonation , schiff base , enol , pyridine , computational chemistry , solvent , crystallography , stereochemistry , organic chemistry , ion , catalysis
This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non‐heterocyclic, tautomeric solids. Quantum‐chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3‐methoxysalicylaldehyde and 2‐amino‐3‐hydroxypyridine ( ap ), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen‐bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap . The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid‐state and solvent‐mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.