Cobalt(II), nickel(II), and copper(II) bromide complexes with 3-amino-4-ethoxycarbonylpyrazole: Syntheses, structures, and magnetic properties

New complexes of cobalt(II), nickel(II), and copper(II) bromides with 3-amino-4-ethoxycarbo- nylpyrazole (L) of the composition ML 4 Br 2 · 2H 2 O (M = Co(II) and Ni(II)) and CuL 2 Br 2 are synthesized. The compounds are studied by X-ray diffraction analysis (CIF files CCDC nos. 1006284 ( I ), 1006286 ( II ), and 1006285 ( III )), IR spectroscopy, and static magnetic susceptibility. In the complexes, the metal ions are in the distorted octahedral environment and the ligand is coordinated to the metal by the N(2) atom of the pyrazole cycle according to the monodentate mode. The Co(II) and Ni(II) complexes are mononuclear, whereas CuL 2 Br 2 is polynuclear due to the bridging function of the bromide ion. Complex CuL 2 Br 2 possesses the thermochromic properties: the transition of the color is brown (at room temperature) ⇔ light brown (at the temperature of liquid nitrogen).