This research work presents one pot synthesis of ternary copper(II) carboxylates of N,Nchelating diamine ligands. The carboxylate ligands used were sodium salts of benzoic acid, 2-chlorobenzoic acid, cinnamic acid, succinic acid, phthalic acid, terephthal ic acid, 4- aminobenzoic acid, 3-aminobenzoic acid, mefenamic acid, acetyl salicylic acid, and tartaric acid. The N,N-chelating diamines utilized include N,N,N′,N′-tetramethylethylenediamine (tmen), while some complexes of carboxylates with ethylenediamine (en), 1,10– phenanthroline (phen) and 2,2′–bipyridine (bipy) have also been prepared. The structural aspects and geometrical assignments related to the synthesized complexes have been investigated with the help of analytical techniques like FT-IR, UV-Visible spectroscopy, thermal studies (TGA) and single crystal X-ray diffraction analysis. The investigated ternary copper(II) complexes involving N,N,N′,N′-tetramethylethylenediamine (tmen) include [Cu(tmen)(BA)2(H2O)2], (1a), [Cu(tmen)(salH)2(H2O)] (2a), {[Cu(tmen)(mef)2] (3a), [Cu(tmen)(pABA)2]. 1/2 MeOH) (4a), [Cu(tmen)(o-ClBA)2] (5a), [Cu(tmen)(cinn)2]. H2O (6a), [Cu(tmen)(phtH)2] (7a), [Cu(tmen)(tpht)(H2O)2]n (8a), {[Cu(tmen)(succin)]n.4H2O} (9a), {[Cu(tmen)(tart)]·2H2O}n (10a). Single crystal analyses of the prepared complexes have revealed that most of the Cu(II)-N,N,N′,N′-tetramethylethylenediamine adducts with the carboxylate ligands are mononuclear, in which N,N,N′,N′-tetramethylethylenediamine is coordinated to Cu(II) in an invariably chelating bidentate mode. In these complexes, the carboxylate moiety belonging to a carboxylate ligand is coordinated to the central Cu(II) ion, either in a monodentate (1a, 2a, 4a, 7a), or bidentate (3a, 5a, 6a) fashion. These mononuclear complexes can be; four-coordinate (4a), with a square planar environment, five-coordinate (2a, 7a),with a square pyramidal geometry, or six-coordinate (1a, 3a, 5a, 6a ) with an octahedral coordination geometry. Three complexes of Cu-tmen-carboxylato series are polynuclear in nature (8a, 9a, 10a) and adopt an octahedral coordination environment. The carboxylate functionality varies in coordination modes, from bis-monodentate bridging (8a) to chelating bridging (9a-10a). Another mixed ligand copper(II) complex incorporating ethylenediamine and salicylate [Cu(en)(salH)Cl]n (where en= ethylenediamine, salH1- = (salicylate1-) (11a) has also been synthesized. The complex [Cu(en)(salH)Cl]n (11a) is found to be unprecedented because of ix the presence of [Cu-Cl]n back-bone formed by central Cu(II) ion and bridging Cl atoms, also it had both ethylenediamine and salicylic acid as a part of the inner coordination sphere, while in most of the known examples, carboxylates usually are found lying uncoordinated in the outer sphere. Two ternary copper(II) carboxylate complexes, containing 2,2′-bipyridine (bipy = C10H8N2) having the formulae [Cu(bipy)(cinn)2(H2O)] (1b) [Cu2(bipy)2(pABA)3(pABAH)]. Cl. 3H2O (2b) {(where cinn1- = cinnamate (C9H7O2 1-) anion, pABA1- = p-amino benzoate (C7H6NO2 1-) anion, and pABAH = p-amino benzoic acid (C7H7NO2)} have been prepared and characterized. The mononuclear ternary Cu(II) complex incorporating 2,2′–bipyridine and cinnamate as shown by single crystal X-ray analyses is found to be square pyramidal, formed by the coordination of bidentate 2,2′–bipyridine, and two monodentate carboxylate groups from two cinnamates, while the apical position is occupied by an aqua-O atom. The second dinuclear mixed ligand Cu(II) complex of 2,2′–bipyridine and p-aminobenzoate (1b) is also found to be unique. It has two copper(II) centers in square pyramidal environments, which are interlinked by two bridging p-aminobenzoates and by two 2,2′–bipyridine ligands in a chelating mode. One remaining p-aminobenzoate is attached through its carboxylato-O atom in a traditional monodentate mode, while the other pABAH is attached to copper(II) through its N atom. Two novel mixed ligand copper(II)-phen based carboxylate complexes represented as [Cu(phen)(benzoate)2] 1c, and [Cu(phen)(m-amb)Cl·½H2O] 2c (where phen = 1,10- phenanthroline, BA1- = benzoate, m-ABA1- = m-aminobenzoate) have been synthesized and characterized. The geometry and structure of the mononuclear ternary Cu(II) complex incorporating 1,10–phenanthroline and m-aminobenzoate, as confirmed through single crystal X-ray analyses is found to be square pyramidal, formed by the coordination of chelating 1,10–phenanthroline, a chelating m-aminobenzoate, while the apical position is occupied by a Cl atom. The second monomeric complex [Cu(phen)(benzoate)2] was square planar, with one bidentate phen and two monodentate benzoates. Antimicrobial studies of complexes have also been performed. Some of these copper(II) complexes are found to be biologically active against bacteria.