3,5-Pyrazoledicarboxylic acid

white crystalline powder

3,5-Pyrazoledicarboxylic acid serves as a ligand for synthesizing metal complexes and coordination polymers. It forms complexes with lanthanides such as cerium(III), lanthanum(III), neodymium(III), praseodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, and erbium. These ligands function as effective bridges to assemble lanthanide-based metal-organic frameworks (MOFs) with varied photophysical and magnetic properties. Hydrothermal reactions of the acid with simple alkaline salts or hydroxides yield new coordination compounds at different pH levels. In mixed-ligand systems, 3,5-pyrazoledicarboxylic acid is used with oxalic acid and terbium nitrate in hydrothermal synthesis to produce specific lanthanide complexes[1-4].

3,5-dimethylpyrazole (4.8g, 50mmol) and 40mL water were added to a 100mL three-necked flask, stirred at 60C, potassium permanganate (31.9g, 200mmol) was added in batches, the reaction temperature was kept at 85-90C, and the reaction was carried out for 2 hours, filtered, washed, and the filtrate was adjusted with concentrated hydrochloric acid to a pH 5-6, filtered, and dried to obtain 3,5-pyrazole dicarboxylic acid 5.4g, yield 69.2%, melting point (decomposition) 290-293 .

It crystallises from water as a monohydrate, or EtOH. Dry it in a vacuum at 100o. The dimethyl ester crystallises from *C6H6 with m 155o. [Beilstein 25 III/IV 1047.]

[1] Peica, N., Kostova, I., Kiefer, W. (2006). Theoretical and experimental studies on binding mode of 3,5-pyrazoledicarboxylic acid in its new La(III) complex. Chemical Physics, 325(2-3), 411–421. https://doi.org/10.1016/j.chemphys.2006.01.017
[2] Kostova, I., Momekov, G. (2008). Synthesis, spectral and pharmacological studies on lanthanide(III) complexes of 3,5-pyrazoledicarboxylic acid. Journal of Coordination Chemistry, 61(23), 3776–3792. https://doi.org/10.1080/00958970802155321
[3] Kostova, I., Peica, N., Kiefer, W. (2006). Raman, FT‐IR, and DFT studies of 3,5‐pyrazoledicarboxylic acid and its Ce(III) and Nd(III) complexes. Journal of Raman Spectroscopy, 38(1), 1–10. https://doi.org/10.1002/jrs.1562
[4] Wu, H.-Y., Yue, S.-T., Wang, N., Liu, Y.-L. (2010). Two lanthanide luminescent coordination compounds based on 3,5-pyrazoledicarboxylate and oxalic acid. Journal of Coordination Chemistry, 63(5), 785–793. https://doi.org/10.1080/00958971003645938