Engineering and functionality of new molecular materials based on 1, 2, 4-triazole building blocks : from molecular sensors to metal-organic/amino-acid frameworks

(eng) Spin crossover (SCO) molecular switches have emerged as remarkable functional materials. Novel Fe8 SCO 1D chains with 4-amino-1,2,4-triazole (NH2trz) and diverse fluorinated inorganic anions varying in geometry/size/charge were investigated and a data bank based on the transition temperature and anions volume was delineated. Further insights on the role of anionic sublattice were gained thanks to 119Sn Mössbauer spectroscopy. The origin of the large hysteresis loop, accompanying the SCO in 1D chains as revealed and attributed to an extensive intra and inter molecular H-bonding network involving the counter anion. The precursor NH2trz was modified into 4-hydroxy-1,2,4-triazole and new Fe(II) chains were prepared. For the first time 1,2,4-triazole derivatives of - and  -aminoesters were designed and introduced to produce new SCO 1D coordination polymers. A strong sensitivity of the SCO behavior was observed on increasing carbon spacer on going toAlatrz. An atypical two-step SCO behavior was thoroughly probed by spectroscopic studies. Further, an acid analogue, 4H-1,2,4-triazol-4-yl acetic acid, has been engineered and introduced as a superlative supramolecular synthon which has interesting topology wherein the two extremities are occupied by two potentially coordinating groups. Diverse topologies ranging from a 1D coordination polymer, 2D chiral helicate and a 3D MOF with a unique array of porous nanoballs architecture were obtained and their gas adsorption properties were studied.