The coordination compounds [CoIIICl(DH)2(HL)], where DH - monoanion of dimethylglyoxime, HL – the neutral molecule, obtained by condensation of hydrazide of izonicotinic acid (Haizonic) coordinated to the metal with aromatic dialdehyde, forming Schiff bases: with 2,6-diacetylpyridine (HL1 ) complex 1 or terephthalic aldehyde (HL2 ) – 2, were synthesized and investigated. Although the reaction molar ratio [CoCl(DH)2(Haizonic)] : aldehyde was 2:1, the obtained products are mononuclear compounds, the dialdehyde participates in condensation by using one aldehyde group, the other remaining intact. The IR spectra are characterized by absorption bands of ν(OH) and ν(NH) (3623-3300 and 3218 cm-1 ), ν(C = O) (1680-1630 cm1 ); δas(CH3) and δs(CH3) (1427 and respectively 1359-1364 cm-1 ). The most intensive bands in the spectra are δas(NO) (1239-1235cm-1 ) and δs(NO) (1091-1089cm-1 ) indicating the presence of ionizing dimethylglyoxime in the complex.figureFig. 1. The molecular structure of [CoIIICl(DH)2(HL 1 )] (1) X-ray study of compound 1 established that it is a discrete molecular complex and crystallizes with molecule of water as a solvatent in 1:1 molar ratio in the monoclinic space group P21/c. The coordination polyhedron of cobalt atom is octahedral, formed by the N5Cl set of donor atoms. The equatorial plane of octahedron consists from two DH-monoanions, which coordinate through the nitrogen atoms, and are connected with each other by two intramolecular O-H···O hydrogen bonds, forming a pseudomacrocycle in this plane. In one axial position there is Cl atom, and in trans position to it – the molecule of HL1 , coordinated through the nitrogen atom of heterocycle. The interatomic distances Co-N(oxim) are within 1.886(5) - 1.904(5) Å, Co-N(HL1 ) is equal to 1.979(5) Å and Co-Cl - 2.227(2) Å. The study of reaction showed that [CoIIICl(DH)2(Haizonic)] through the coordinated hydrazide of izonicotinic acid participates in the condensation process with aromatic dialdehyde forming the new Schiff bases HL1 and HL2