Novel N–N–N–O-type of tetradentate ligands H3obap (H3obap = oxamido-N-aminopropyl-N0-benzoic acid) and H3maeb (H3maeb = malamido-N-aminoethyl-N0-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap3 and maeb3 ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na2[Cu(obap)]2 Æ 2H2O complex. Structural data correlating the square-planar geometry of the [Cu(obap)] unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.