The reactions of the 4-hydroxy-pyridine-2,6-dicarboxylic acid (for short H3hypydc), 2-aminopyrimidine (for short 2-apym), and 2,4,6-triamino-1,3,5- triazine (for short tata) with nickel(II) chloride and calcium(II) nitrate in distilled water medium produce block green crystals of [Ni(hypydcH) (2- apym)(H2O)2]. H2O (1) and block colourless crystals of (tataH)2 (tata)2 [Ca2(hypydc)2(H2O)6].2H2O (2), respectively. Both crystal structures were thoroughly characterized by CHN elemental analyses, FTIR spectroscopy, TGA, and SXRD methods. 1 and 2 crystallize in the space group P 1 of the triclinic systems, where the final R values for 1 and 2 are 0.0222 for 3876 reflections collected and 0.0550 for 4113 reflections collected, respectively. The unit cell dimensions for 1 are: a = 8.5146(3) Å, b = 9.2662(4) Å, c = 10.1009(4) Å and  = 79.304(1)°,  = 65.206(1)°,  = 84.064(1)° and for 2 are a = 8.6444(7) Å, b = 9.5486(8) Å, c = 14.4025(12) Å and  = 105.296(2)°,  = 95.745(2)°,  = 108.241(2)°. The Ni(II) atom is coordinated by four oxygen and two nitrogen atoms of the (hypydc)2–,(2-apym) and H2O ligands and each Ca(II) atom is coordinated by six oxygen and one nitrogen atoms of the (hypydc)3– and H2O ligands. The coordination geometry around Ni(II) and Ca(II) centres are distorted octahedron and distorted pentagonal bipyramid, respectively.

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