Neutral and anionic duality of 1,2,4-triazole α-amino acid scaffold in 1D coordination polymers

Abstract

A tiny supramolecular synthon, 4H-1,2,4-triazol-4-yl acetic acid (HGlytrz) which is bifunctional by design having an electronic asymmetry and conformational flexibility has been introduced to synthesize iron(II) complexes. Having 1,2,4-triazole or carboxylic extremities on the same framework HGlytrz could display dual functionality by acting as a neutral as well as anionic ligand based on the possibility of deprotonation of carboxylic group. Four new iron(II) HGlytrz complexes with ClO$_{4}^{-}$ (1), NO$_{3}^{-}$ (2), BF$_{4}^{-}$ (3) and CF₃SO$_{3}^{-}$ (4) anions were prepared. Formulation of their composition which is complicated due to ligand deprotonation is discussed. Unlike its ester protected counterpart ethyl-4H-1,2,4-triazol-4-yl-acetate (αGlytrz) which show hysteretic room temperature spin crossover, 1–4 remain in the high-spin state as revealed by ⁵⁷Mössbauer spectroscopy. Prospects of such 1D coordination polymers with dangling unbounded carboxylic entities in the realm of self-assembled monolayer (SAM) are discussed.