A new quadridentate ligand, 3,8-dimethyl-5,6-benzo(15-crown-5)-4,7-diazadeca-3,7 -diene-2,9-dione dioxime (H2L) has been synthesized by the reaction of 4',5'-diaminobenzo (15-crown-5) with diacetyl monoxime. The dibromo complexes of this ligand [Co(HL) Br-2] have been prepared by the direct reaction of H2L with CoBr2. 6H(2)O. Pseudo-halogeno complexes [XCo(HL)Br], where X-CN-, SCN-, N-3(-) or Lewis base complexes [LCo(HL) Br]CLO4, and L pyridine, have been synthesized as a result of the axial lability of [Co(HL)Br-2]. Alkyl and benzyl cobalt(III) complexes [R Co(HL1)L], R Me or PhCH2 have been prepared by the oxidative-addition reaction of the in situ generated Co(I) form of [Co(HL)Br-2] complex with Mel or PhCH2Br and a Lewis base in inert condition. In addition, the heterodinuclear complex containing the oxime to dianion as bridging ligand and 2,2'-bipyridine (L') as end-capping ligand has been synthesized by using [Ni(HL)]ClO4 as the ligand for the MLn+ center. The structures of the dioxime and its complexes are proposed on the basis of elemetal analyses, H-1 and C-13 NMR, IR and MS spectral data.