Liquid-crystalline zinc(II) and iron(II) alkyltriazoles one-dimensional coordination polymers.

Several series of unidimensional coordination polymers of formula [Zn(C(n)H(2n+1)trz)(3)](Cl)(2)·xH(2)O (n = 18, 16, 13, 11, 10, trz = 4-substituted-1,2,4-triazole), [Zn(C(18)H(37)trz)(3)](ptol)(2)·xH(2)O, [Fe(C(n)H(2n+1)trz)(3)](X)(2)·xH(2)O (n = 18, 16, 13, 10; X = Cl(-) or ptol(-), where ptol(-) = p-tolylsulfonate anion), and [Fe(C(18)H(37)trz)(3)](X)(2)·xH(2)O (X = C(8)H(17)PhSO(3)(-) and C(8)H(17)SO(3)(-)) are reported with their thermal, structural, and magnetic properties. Most of these materials exhibit thermotropic lamellar mesophases at temperatures as low as 410 K, as confirmed by textures observed by polarized optical microscopy. The corresponding phase diagrams deduced by differential scanning calorimetry are also reported. All iron-containing materials present a spin crossover phenomenon that occurs at temperatures ranging from 242 to 360 K, only slightly below the mesophase temperature domain, and remains complete and cooperative, even for the longer alkyl substituents. The use of stable diamagnetic Zn(II) analogues proves to be very useful to characterize the comparatively less stable and less crystalline Fe(II) analogues.

Multifunctional gels from polymeric spin-crossover metallo-gelators.

The gelation abilities toward organic solvents of a series of triazole-based coordination polymers of formula [M(C(n)trz)(3)]A(2) (M = Fe(II) or Zn(II); C(n)trz = 4-n-alkyl-1,2,4-triazole with n = 13, 16, 18; A = monovalent anions, abbreviated as MC(n)A) have been studied to form thermally responsive multifunctional metallogels, in particular for the iron polymers that present the spin-crossover phenomenon. Indeed thermo-reversible physical gels exhibiting thermally reversible magnetic and optical crossovers are formed in decane and toluene. The FeC(18)ptol/decane and FeC(18)ptol/toluene phase diagrams are described (ptol = p-toluene sulfonate anion), together with the rheological properties of the gels determined as a function of the solvent, the gelator concentration as well as temperature. Microscopic observations of the gel structure are correlated to the composition and rheological properties of the gels. Magnetic and thermal studies show that both the gel-liquid and spin-crossover phenomena can be adjusted through the composition of the gel mixture.

Shear-induced fractures and three-dimensional motions in an organogel.

The flow behavior of a viscoelastic organogel is investigated using ultrasonic velocimetry combined with rheometry. Our gel presents a decreasing flow curve, i.e., the measured stress decreases as a function of the applied shear rate. Strikingly, we note that the local flow curve calculated from the velocity profiles also exhibits a decreasing part. We attribute this regime to the presence of a fracturing process and three-dimensional motions in the bulk of the sample.