The reactions of pyrrole-2,5-dicarbaldehyde (1) with 2-aminodiphenylamine (3) taken in a ratio of 1 : 2 in the presence of polinuclear nickel(II) and cobalt(II) trimethyl-acetate complexes were studied in MeCN. The reaction with Ni-9(HOOCCMe3)(4)(mu(4)-OH)(3)(mu(3)-OH)(3)(OOCCMe3)(12) (2) afforded the mononuclear complex Ni(OOCCMe3)(2)[(PhHN)C6H4NHCHC4H2NCHNC6H4(NHPh)] (4) with a new ligand, which is the product of condensation of one molecule 1 with two molecules 3 and contains two NHPh groups. By contrast, the reaction with the polymeric complex [Co(OH)n(OOCCMe3)(2-n)](x), (5, n = 0.05-0.1) gave rise to the tetranuclear complex Co-4(mu(4)-O)(mu-OOCCMe3)(4)L-2 (6), where L is, apparently, the product of further oxidation of Schiff's base to the benzimidazole derivative. The structures of compounds 4 and 6 were established by X-ray diffraction analysis.