We have synthesized crystalline complexes from copper(II) salts and pyrazinoic acid. We used copper(II) nitrate, sulfate and chloride, to which we added pyrazinoic acid and a solvent. The syntheses were done in acetonitrile, ethanol or mixtures of these solvents with water. In some experiments we also added concentrated hydrochloric, sulfuric or nitric acid and observed its effect on the reaction.
Most experiments resulted in one of two products, dipyrazinoatocopper(II) [Cu(pyza)$_2$] or diaquadipyrazinoatocopper(II) [Cu(H$_2$O)$_2$(pyza)$_2$]. A complex, in which a molecule of pyrazinoic acid was coordinated, was only produced with the addition of concentrated hydrochloric acid. We isolated a complex with the formula [CuCl$_2$(pyzaH)$_2$]·2H$_2$O. During recrystallization of this product in a closed system at low pressure the crystalline complex [CuCl(H$_2$O)(pyza)]$_n$ was formed. IR spectra were recorded for all products, thermal, elemental, X-ray diffraction and X-ray structural anaylsis were also carried out for some samples.
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