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

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 toAlatrz. 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.(CHIM 3) -- UCL, 201

Room temperature hysteretic spin transition in 1D iron(II) coordination polymers

The 1D spin transition compound [Fe(L1)/sub 3/](ClO/sub 4/)/sub 2/ (1) with L1 = ethyl-4H-1,2,4-triazol-4-yl-acetate, a novel neutral bidentate ligand, has been synthesised. The temperature dependence of the high-spin molar fraction derived from /sup 57/Fe Mossbauer spectroscopy reveals an exceptionally abrupt single step transition between low-spin and high-spin states with a hysteresis loop of width 5 K ( T/sub c//sup ^/ = 298 K and T/sub c//sup darr / = 293 K). This spin transition operating around room temperature presents striking reversible thermochromism from white at 295 K to pink at ice temperature, behaving as an optical alert towards temperature variations. This first order phase transition was additionally followed by differential scanning calorimetry in good agreement with Mössbauer spectroscopy data. The spin transition properties of a freshly prepared sample of 1 , dried under a N/sub 2/ (g) stream which was formulated as [Fe(L1)/sub 3/](ClO/sub 4/)/sub 2/ middot MeOH (2), are shifted below room temperature ( T/sub 1/2//sup ^/ = 273 K and T/sub 1/2//sup darr / = 263 K), thus showing a remarkable influence of solvent inclusion on the spin state of these chain compounds.Anglai

Iron(II) spin transition 1,2,4-triazole chain compounds with novel inorganic fluorinated counteranions

New one-dimensional spin transition coordination polymers of formula [Fe(NH(2)trZ)(3)](AF(6)) center dot nH(2)O (A = Ti, Zr, Sn; NH(2)trz = 4-amino-1,2,4-triazole) have been synthesized in MeOH and EtOH media. These materials display an abrupt and hysteretic spin transition around 200 K as well as a reversible thermochromic effect on, cooling. A preliminary evaluation of the lattice dynamics in the high-spin and low-spin states is presented. (c) 2006 Elsevier Ltd. All rights reserved

Coordination polymers and metal organic frameworks derived from 1,2,4-triazole amino acid linkers

The perceptible appearance of biomolecules as prospective building blocks in the architecture of coordination polymers (CPs) and metal-organic frameworks (MOFs) are redolent of their inclusion in the synthon/tecton library of reticular chemistry. In this frame, for the first time a synthetic strategy has been established for amine derivatization in amino acids into 1,2,4-triazoles. A set of novel 1,2,4-triazole derivatized amino acids were introduced as superlative precursors in the design of 1D coordination polymers, 2D chiral helicates and 3D metal-organic frameworks. Applications associated with these compounds are diverse and include gas adsorption-porosity partitioning, soft sacrificial matrix for morphology and phase selective cadmium oxide synthesis, FeII spin crossover materials, zinc-b-lactamases inhibitors, logistics for generation of chiral/non-centrosymmetric networks; and thus led to a foundation of a new family of functional CPs and MOFs that are reviewed in this invited contribution

Rapid Cooling Experiments and Use of an Anionic Nuclear Probe to Sense the Spin Transition of the 1D Coordination Polymers [Fe(NH(2)trz)(3)]SnF(6)n H(2)O (NH(2)trz=4-amino-1,2,4-triazole).

[Fe(NH(2)trz)(3)]SnF(6)n H(2)O (NH(2)trz=4-amino-1,2,4-triazole; n=1 (1), n=0.5 (2)) are new 1D spin-crossover coordination polymers. Compound 2 exhibits an incomplete spin transition centred at around 210 K with a thermal hysteresis loop approximately 16 K wide. The spin transition of 2 was detected by the Mössbauer resonance of the (119)Sn atom in the SnF(6) (2-) anion primarily on the basis of the evolution of its local distortion. Rapid-cooling (57)Fe Mössbauer and superconducting quantum interference device experiments allow dramatic widening of the hysteresis width of 2 from 16 K up to 82 K and also shift the spin-transition curve into the room temperature region. This unusual behaviour of quenched samples on warming is attributed to activation of the molecular motion of the anions from a frozen distorted form towards a regular form at temperatures well above approximately 210 K. Potential applications of this new family of materials are discussed

Calorimetric measurements of diluted spin crossover complexes [FexM1-x(btr)(2)(NCS)(2)]center dot H2O with M-II = Zn and Ni

Motivated by the application of the First Order Reversal Curve (FORC) technique to obtain a distribution of like spin domains in the spin crossover complexes [FexM1-x(btr)(2)(NCS)(2)]center dot H2O with M-II = Zn and Ni, we have performed Differential Scanning Calorimetry (DSC) experiments. We have measured the heat capacity in the heating and cooling modes and then calculated the enthalpy and the entropy variations at the phase transition. In the framework of an Ising-like model, we have converted the experimental thermal hysteresis into terms of physical parameters related to these compounds. We have also performed a statistical analysis of these parameters and concluded that the correlation between them increases with the dilution degree of these spin crossover complexes. (C) 2009 Elsevier Ltd. All rights reserved