The Iron(II) complex with 4-amino-1,2,4 triazole (NH2-trz) ligand has potential applications as smart material since the compounds show a distinct color change from lilac at low temperature to colorless at high temperature. The lilac color of the complex represent the diamagnetic low spin state while the colorless correspond to the paramagnetic high spin state of iron(II). The transition between the two states could be tuned by changing the anionic group. Generally, the complex was synthesized directly from aqueous solution of iron(II) salt with considerable amounts of NH2-trz solution produced solid powder compound. For application as an electronic molecular device, the complex should be obtained as a thin film. The transparent [Fe(NH(2)trz)(3)]-Nafion film has been successfully obtained, however, no anion variation can be produced since the nation is an anionic resin. In this work, the [Fe(NH(2)trz)(3)]-complexes with several anions have been synthesized inside nolo de coco membrane that commonly used as a medium for deposition metal nano-particles. After drying the membrane containing the complex became a thin film At room temperature, the film containing iron(II) complexes of sulphate and nitrate salts show lilac color, similar to that of the original complexes in the powder form. On heating, the color of the complex film changed to colorless and this color change was observed reversibly. In contrast, the films containing perchlorate and tetrafluoroborate iron(II) complexes are colorless at room temperature and changed to lilac on cooling. The significant color changing of the iron(II)complexes in the nata de cow film can be used for demonstration thermo chromic effect of smart materials with relatively small amount of the compounds.