Synthesis and structure of new mononuclear octahedral cobalt(III) dioximates derived from isonicotinic hydrazide

•New Schiff base resulting from isonicotinic hydrazide and 2,4-pentanedione.•Compounds comprise novel ligand and its dehydrated derivative.•Mononuclear octahedral complex [Co(DfgH)2BrL] with the substitution of the water molecule by new ligand.•Co(III) complex [Co(DmgH)2ClL′], where L′ represents a dehydrated derivative of L.•The crystal structures were studied.

New organic ligand L (1) resulting from isonicotinic hydrazide and 2,4-pentanedione has been prepared and investigated by physicochemical methods, including elemental analysis, 1H and 13C NMR, IR spectroscopy and X-ray studies.The X-ray investigation revealed that the condensation of 2,4-pentanedione with isonicotinic hydrazide is accompanied by the formation of a five-membered ring including three carbon atoms of 2,4-pentanedione and two nitrogen atoms of the isonicotinic hydrazide fragment.The reaction between [Co(DfgH)2Br(H2O)] (DfgH2 = diphenylglyoxime) and L resulted in the formation of the mononuclear octahedral complex [Co(DfgH)2BrL] (2) with the substitution of the water molecule in the apical position by the ligand L. The reaction starting from [Co(DmgH)2Cl(H2O)] (DmgH = dimethylglyoxime) and L resulted in the mononuclear octahedral Co(III) complex with the composition [Co(DmgH)2ClL′] (3), where L′ unexpectedly represents a dehydrated derivative of L. The two coordination compounds are characterized by X-ray diffraction method. The IR, 1H NMR spectral studies of new compounds are also reported.