Several series of unidimensional coordination polymers of formula [Zn(C(5)H(2n+1)trz)(3)](Cl)(2)center dot 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)center dot xH(2)O, [Fe(C(n)H(2n+1)trz)(3)](X)(2)center dot 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)center dot xH(2)O (X = C8H17PhSO3- and C8H17SO3-) 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.