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

A versatile iron(II)-based colorimetric sensor for the vapor-phase detection of alcohols and toxic gases

A mononuclear iron(II) neutral complex (1) was screened for colorimetric sensing abilities for a wide spectrum of vapor-phase analytes including toxic gases. Although 1 possesses a single sensing unit without any other cross-reactive elements, it can capture information about analyte molecules in a distributed fashion that is encoded sufficiently to allow discrimination from other closely related chemical structures. Clear color differentiation among four different toxic industrial chemicals (TICs) and alcohols was demonstrated. Different TICs and alcohols were readily identified using a standard chemometric approach (hierarchical clustering analysis), with no misclassifications over 18 trials. 57Fe Mo¨ssbauer spectroscopy was applied to investigate the driving spin state change of the analytes in this Fe-azole sensor material. This approach opens up perspectives for the further development of iron materials as potential optical sensor arrays through colorimetric techniques

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

Insights into the Origin of Cooperative Effects in the Spin Transition of [Fe(NH(2)trz)(3)](NO(3))(2): the Role of Supramolecular Interactions Evidenced in the Crystal Structure of [Cu(NH(2)trz)(3)](NO(3))(2).H(2)O.

The thermally induced hysteretic spin transition (ST) that occurs in the polymeric chain compound [Fe(NH(2)trz)(3)](NO(3))(2) (1) above room temperature (T(c)( upward arrow) = 347 K, T(c)( downward arrow) = 314 K) has been tracked by (57)Fe Mossbauer spectroscopy, SQUID magnetometry, differential scanning calorimetry (DSC), and X-ray powder diffraction (XPRD) at variable temperatures. From the XRPD pattern indexation, an orthorhombic primitive cell was observed with the following cell parameters: a = 11.83(2) A, b = 9.72(1) A, c = 6.361(9) A at 298 K (low-spin state) and a = 14.37(2) A, b = 9.61(4) A, c = 6.76(4) A at 380 K (high-spin state). The enthalpy and entropy variation associated to the ST of 1, have been evaluated by DSC as DeltaH = 23(1) kJ mol(-1) and DeltaS = 69.6(1) J mol(-1) K(-1). These thermodynamic data were used within a two-level Ising like model for the statistical analysis of First Order Reversal Curve (FORC) diagram that was recorded for 1, in the cooling mode. Strong intramolecular cooperative effects are witnessed by the derived interaction parameter of J = 496 K. The crystal structure of [Cu(NH(2)trz)(3)](NO(3))(2).H(2)O (2) was obtained thanks to high quality single crystals prepared by slow evaporation after hydrothermal pretreatment. The catena poly[mu-tris(4-amino-1,2,4-triazole-N1,N2) copper(II)] dinitrate monohydrate (2) crystallizes in the monoclinic space group C2/c, with a = 16.635(6) A, b = 13.223(4) A, c = 7.805(3) A, beta = 102.56(3) degrees , Z = 4. Complex 2 is a 1D infinite chain containing triple N1,N2-1,2,4-triazole bridges with an intra-chain distance of Cu...Cu = 3.903(1) A. A dense H-bonding network with the nitrate counteranion involved in intra-chain and inter-chain interactions is observed. Such a supramolecular network could be at the origin of the unusually large hysteresis loop displayed by 1 (DeltaT approximately 33 K), as a result of an efficient propagation of elastic interactions through the network. This hypothesis is strengthened by the crystal structure of 2 and by the absence of crystallographic phase transition for 1 over the whole temperature range of investigation as shown by XRPD

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