We conducted reactions between nickel(II) chloride, nickel(II) nitrate hexahydrate, nickel(II) sulfate heptahydrate, zinc chloride, or zinc acetate dihydrate and pyrazole-3-carboxylic acid (H$_2$pza) in water, methanol, pyridine, or acetonitrile with a catalytic amount of hydrochloric acid. The molar ratio of nickel or zinc ions to H$_2$pza was 2 : 1. Reactions were carried out in water at 80 °C and in other solvents at room temperature. Crystallizations were performed in air at room temperature or in a closed system under reduced pressure. We isolated crystals of the known compounds [Ni(Hpza)$_2$(H$_2$O)$_2$] and [Zn(Hpza)$_2$(H$_2$O)$_2$], as confirmed by X-ray structure analysis. We also synthesized four new compounds: [Ni(Hpza)$_2$(py)$_2$]$_2$⋅py, [NiCl$_2$(HpzaMe)$_2$], [NiCl$_2$(H$_2$pza)$_2$]⋅2H$_2$O, and [ZnCl$_2$(HpzaMe)$_2$]. The structures of [Ni(Hpza)$_2$(py)$_2$]$_2$⋅py and [ZnCl$_2$(HpzaMe)$_2$] were determined by X-ray structural analysis. We also used other analytical methods such as infrared spectroscopy, CHN elemental analysis, and thermal analysis. We concluded that the processes of H$_2$pza deprotonation and Hpza$^–$ coordination to the nickel or zinc ion occurred in water without the addition of hydrochloric acid to the reaction mixture. In methanol, with the addition of hyrdochloric acid, H$_2$pza reacted and formed an ester; thus, two molecules of the ester HpzaMe coordinated to the nickel or zinc ion under these conditions. In the aprotic solvent acetonitrile, in the presence of hydrochloric acid, deprotonation of H$_2$pza did not occur, and two molecules of H$_2$pza coordinated to the nickel ion.
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